PMCC PMCC

Search tips
Search criteria

Advanced
Results 1-25 (67)
 

Clipboard (0)
None

Select a Filter Below

Journals
more »
Year of Publication
Document Types
1.  25-hydroxyvitamin D Levels after Recovery from Tuberculosis: Insights into Pathogenesis 
Objective
25-hydroxyvitamin D [25(OH)D] levels after recovery from tuberculosis (TB) may reflect pre-morbid levels and therefore provide insight into pathogenesis. We assessed 25(OH)D levels after recovery from TB disease, and compared to levels in persons without TB disease.
Methods
Case-control study. Cases were persons who had recovered from culture-confirmed Mycobacterium tuberculosis disease. Controls were persons without TB disease. Total 25(OH)D was measured from stored plasma specimens using liquid chromatography-mass spectrometry.
Results
29 persons with prior TB disease and 36 controls were included. Median 25(OH)D levels were 24.7 ng/mL (IQR, 18.3–34.1) in prior TB disease, and 33.6 ng/mL (IQR, 26.2–42.4) in controls (Mann-Whitney; P=0.01). Multivariable linear regression analysis showed that black race (adjusted mean difference [β]=−8.3 ng/mL; 95% CI −14.5, −2.2; P<0.01), enrollment in winter (β=−10.4 ng/mL; 95% CI −17.0, −3.8; P<0.01) and prior TB disease (β=−5.8 ng/mL; 95% CI −11.4, −0.3; P=0.05) were associated with lower 25(OH)D levels.
Conclusions
Persons who had recovered from TB disease had lower 25(OH)D levels compared to controls without TB disease, after adjusting for important confounders. Larger, longitudinal studies are needed to further characterize the possible role of low 25(OH)D in the pathogenesis of TB disease and TB recurrence after recovery.
doi:10.1016/j.tube.2013.10.009
PMCID: PMC3938285  PMID: 24275362
25-hydroxyvitamin D; vitamin D; tuberculosis; Mycobacterium tuberculosis
2.  Impact of Definitions of Loss to Follow-up on Estimates of Retention, Disease Progression, and Mortality: Application to an HIV Program in Mozambique 
American Journal of Epidemiology  2013;178(5):819-828.
Patient retention is critical to the management of chronic diseases such as human immunodeficiency virus (HIV); hence, accurate measures of loss to follow-up (LTF) are important. Many different LTF definitions have been proposed. In a cohort of 9,692 HIV-infected patients initiating antiretroviral therapy in Mozambique from 2006 to 2011, we investigated the impact of the definition of LTF on estimated rates of LTF, acquired immunodeficiency syndrome (AIDS)-defining events, and death by applying 17 different definitions of LTF gleaned from HIV literature. We further investigated the impact of 4 specific components of the LTF definitions. Cumulative incidences of LTF and AIDS-defining events were estimated by treating death as a competing risk; Kaplan-Meier techniques and variations to account for informative censoring were used to estimate rates of mortality. Estimates of LTF 2 years after treatment initiation were high and varied substantially, from 22% to 84% depending on the LTF definition used. Estimates of 2-year mortality varied from 11% to 16%, and estimates of 2-year AIDS-defining events varied from 6% to 8%. As seen here, the choice of LTF definition can greatly affect study conclusions and program evaluations. Selection of LTF definitions should be based on the study outcome, available data on clinical encounters, and the patients' visit schedules; we suggest some general guidelines.
doi:10.1093/aje/kwt030
PMCID: PMC3755641  PMID: 23785113
chronic disease; cohort studies; HIV; long-term care; lost to follow-up; program evaluation
3.  HIV and cancer: a comparative retrospective study of Brazilian and U.S. clinical cohorts 
Background
With successful antiretroviral therapy, non-communicable diseases, including malignancies, are increasingly contributing to morbidity and mortality among HIV-infected persons. The epidemiology of AIDS-defining cancers (ADCs) and non-AIDS-defining cancers (NADCs) in HIV-infected populations in Brazil has not been well described. It is not known if cancer trends in HIV-infected populations in Brazil are similar to those of other countries where antiretroviral therapy is also widely available.
Methods
We performed a retrospective analysis of clinical cohorts at Instituto Nacional de Infectologia Evandro Chagas (INI) in Rio de Janeiro and Vanderbilt Comprehensive Care Clinic (VCCC) in Nashville from 1998 to 2010. We used Poisson regression and standardized incidence ratios (SIRs) to examine incidence trends. Clinical and demographic predictors of ADCs and NADCs were examined using Cox proportional hazards models.
Results
This study included 2,925 patients at INI and 3,927 patients at VCCC. There were 57 ADCs at INI (65% Kaposi sarcoma), 47 at VCCC (40% Kaposi sarcoma), 45 NADCs at INI, and 82 at VCCC. From 1998 to 2004, incidence of ADCs remained statistically unchanged at both sites. From 2005 to 2010, ADC incidence decreased in both cohorts (INI incidence rate ratio per year = 0.74, p < 0.01; VCCC = 0.75, p < 0.01). Overall Kaposi sarcoma incidence was greater at INI than VCCC (3.0 vs. 1.2 cases per 1,000 person-years, p < 0.01). Incidence of NADCs remained constant throughout the study period (overall INI incidence 3.6 per 1,000 person-years and VCCC incidence 5.3 per 1,000 person-years). Compared to general populations, overall risk of NADCs was increased at both sites (INI SIR = 1.4 [95% CI 1.1-1.9] and VCCC SIR = 1.3 [1.0-1.7]). After non-melanoma skin cancers, the most frequent NADCs were anal cancer at INI (n = 7) and lung cancer at VCCC (n = 11). In multivariate models, risk of ADC was associated with male sex and immunosuppression. Risk of NADC was associated with increased age.
Conclusions
In both cohorts, ADCs have decreased over time, though incidence of KS was higher at INI than VCCC. Rates of NADCs remained constant over time at both sites.
Electronic supplementary material
The online version of this article (doi:10.1186/1750-9378-10-4) contains supplementary material, which is available to authorized users.
doi:10.1186/1750-9378-10-4
PMCID: PMC4327947
HIV; Malignancy; Cancer; Brazil; Anal cancer; Kaposi sarcoma; Non-Hodgkin lymphoma; Lung cancer; Age; Sex
4.  Poor Clinical Outcomes for HIV Infected Children on Antiretroviral Therapy in Rural Mozambique: Need for Program Quality Improvement and Community Engagement 
PLoS ONE  2014;9(10):e110116.
Introduction
Residents of Zambézia Province, Mozambique live from rural subsistence farming and fishing. The 2009 provincial HIV prevalence for adults 15–49 years was 12.6%, higher among women (15.3%) than men (8.9%). We reviewed clinical data to assess outcomes for HIV-infected children on combination antiretroviral therapy (cART) in a highly resource-limited setting.
Methods
We studied rates of 2-year mortality and loss to follow-up (LTFU) for children <15 years of age initiating cART between June 2006–July 2011 in 10 rural districts. National guidelines define LTFU as >60 days following last-scheduled medication pickup. Kaplan-Meier estimates to compute mortality assumed non-informative censoring. Cumulative LTFU incidence calculations treated death as a competing risk.
Results
Of 753 children, 29.0% (95% CI: 24.5, 33.2) were confirmed dead by 2 years and 39.0% (95% CI: 34.8, 42.9) were LTFU with unknown clinical outcomes. The cohort mortality rate was 8.4% (95% CI: 6.3, 10.4) after 90 days on cART and 19.2% (95% CI: 16.0, 22.3) after 365 days. Higher hemoglobin at cART initiation was associated with being alive and on cART at 2 years (alive: 9.3 g/dL vs. dead or LTFU: 8.3–8.4 g/dL, p<0.01). Cotrimoxazole use within 90 days of ART initiation was associated with improved 2-year outcomes Treatment was initiated late (WHO stage III/IV) among 48% of the children with WHO stage recorded in their records. Marked heterogeneity in outcomes by district was noted (p<0.001).
Conclusions
We found poor clinical and programmatic outcomes among children taking cART in rural Mozambique. Expanded testing, early infant diagnosis, counseling/support services, case finding, and outreach are insufficiently implemented. Our quality improvement efforts seek to better link pregnancy and HIV services, expand coverage and timeliness of infant diagnosis and treatment, and increase follow-up and adherence.
doi:10.1371/journal.pone.0110116
PMCID: PMC4203761  PMID: 25330113
5.  A 12 week longitudinal study of microbial translocation and systemic inflammation in undernourished HIV-infected Zambians initiating antiretroviral therapy 
BMC Infectious Diseases  2014;14(1):521.
Background
Undernourished, HIV-infected adults in sub-Saharan Africa have high levels of systemic inflammation, which is a risk factor for mortality and other adverse health outcomes. We hypothesized that microbial translocation, due to the deleterious effects of HIV and poor nutrition on intestinal defenses and mucosal integrity, contributes to heightened systemic inflammation in this population, and reductions in inflammation on antiretroviral therapy (ART) accompany reductions in translocation.
Methods
HIV-infected, Zambian adults with a body mass index <18.5 kg/m2 were recruited for a pilot study to assess the relationships between microbial translocation and systemic inflammation over the first 12 weeks of ART. To assess microbial translocation we measured serum lipopolysaccharide binding protein (LBP), endotoxin core IgG and IgM, and soluble CD14, and to assess intestinal permeability we measured the urinary excretion of an oral lactulose dose normalized to urinary creatinine (Lac/Cr ratio). Linear mixed models were used to assess within-patient changes in these markers relative to serum C-reactive protein (CRP), tumor necrosis factor-α receptor 1 (TNF-α R1), and soluble CD163 over 12 weeks, in addition to relationships between variables independent of time point and adjusted for age, sex, and CD4+ count.
Results
Thirty-three participants had data from recruitment and at 12 weeks: 55% were male, median age was 36 years, and median baseline CD4+ count was 224 cells/μl. Over the first 12 weeks of ART, there were significant decreases in serum levels of LBP (median change -8.7 μg/ml, p = 0.01), TNF-α receptor 1 (-0.31 ng/ml, p < 0.01), and CRP (-3.5 mg/l, p = 0.02). The change in soluble CD14 level over 12 weeks was positively associated with the change in CRP (p < 0.01) and soluble CD163 (p < 0.01). Pooling data at baseline and 12 weeks, serum LBP was positively associated with CRP (p = 0.01), while endotoxin core IgM was inversely associated with CRP (p = 0.01) and TNF-α receptor 1 (p = 0.04). The Lac/Cr ratio was not associated with any serum biomarkers.
Conclusions
In undernourished HIV-infected adults in Zambia, biomarkers of increased microbial translocation are associated with high levels of systemic inflammation before and after initiation of ART, suggesting that impaired gut immune defenses contribute to innate immune activation in this population.
Electronic supplementary material
The online version of this article (doi:10.1186/1471-2334-14-521) contains supplementary material, which is available to authorized users.
doi:10.1186/1471-2334-14-521
PMCID: PMC4261887  PMID: 25266928
HIV infection; Antiretroviral therapy; Microbial translocation; Nutrition; Sub-Saharan Africa; Inflammation
6.  Sexual Risk Reduction for HIV-Infected Persons: A Meta-Analytic Review of “Positive Prevention” Randomized Clinical Trials 
PLoS ONE  2014;9(9):e107652.
Background
Prevention intervention trials have been conducted to reduce risk of sexual transmission among people living with HIV/AIDS (PLWHA), but the findings were inconsistent. We performed a systematic review and meta-analysis to evaluate overall efficacy of prevention interventions on unprotected vaginal or anal intercourse (UVAI) among PLWHA from randomized clinical trials (RCTs).
Methods
RCTs of prevention interventions among PLWHA published as of February 2012 were identified by systematically searching thirteen electronic databases. The primary outcome was UVAI. The difference of standardized mean difference (SMD) of UVAI between study arms, defined as effect size (ES), was calculated for each study and then pooled across studies using standard meta-analysis with a random effects model.
Results
Lower likelihood of UVAI was observed in the intervention arms compared with the control arms either with any sexual partners (mean ES: −0.22; 95% confidence interval [CI]: −0.32, −0.11) or with HIV-negative or unknown-status sexual partners (mean ES and 95% CI: −0.13 [−0.22, −0.04]). Short-term efficacy of interventions with ≤10 months of follow up was significant in reducing UVAI (1–5 months: −0.27 [−0.45, −0.10]; 6–10 months: −0.18 [−0.30, −0.07]), while long-term efficacy of interventions was weaker and might have been due to chance (11–15 months: −0.13 [−0.34, 0.08]; >15 months: −0.05 [−0.43, 0.32]).
Conclusions
Our meta-analyses confirmed the short-term impact of prevention interventions on reducing self-reported UVAI among PLWHA irrespective of the type of sexual partner, but did not support a definite conclusion on long-term effect. It is suggested that booster intervention sessions are needed to maintain a sustainable reduction of unprotected sex among PLWHA in future risk reduction programs.
doi:10.1371/journal.pone.0107652
PMCID: PMC4171502  PMID: 25243404
7.  Use of Third Line Antiretroviral Therapy in Latin America 
PLoS ONE  2014;9(9):e106887.
Background
Access to highly active antiretroviral therapy (HAART) is expanding in Latin America. Many patients require second and third line therapy due to toxicity, tolerability, failure, or a combination of factors. The need for third line HAART, essential for program planning, is not known.
Methods
Antiretroviral-naïve patients ≥18 years who started first HAART after January 1, 2000 in Caribbean, Central and South America Network (CCASAnet) sites in Argentina, Brazil, Honduras, Mexico, and Peru were included. Clinical trials participants were excluded. Third line HAART was defined as use of darunavir, tipranavir, etravirine, enfuvirtide, maraviroc or raltegravir. Need for third line HAART was defined as virologic failure while on second line HAART.
Results
Of 5853 HAART initiators followed for a median of 3.5 years, 310 (5.3%) failed a second line regimen and 44 (0.8%) received a third line regimen. Cumulative incidence of failing a 2nd or starting a 3rd line regimen was 2.7% and 6.0% three and five years after HAART initiation, respectively. Predictors at HAART initiation for failing a second or starting a third line included female sex (hazard ratio [HR] = 1.54, 95% confidence interval [CI] 1.18–2.00, p = 0.001), younger age (HR = 2.76 for 20 vs. 40 years, 95% CI 1.86–4.10, p<0.001), and prior AIDS (HR = 2.17, 95% CI 1.62–2.90, p<0.001).
Conclusions
Third line regimens may be needed for at least 6% of patients in Latin America within 5 years of starting HAART, a substantial proportion given the large numbers of patients on HAART in the region. Improved accessibility to third line regimens is warranted.
doi:10.1371/journal.pone.0106887
PMCID: PMC4164470  PMID: 25221931
8.  Mortality in Patients with HIV-1 Infection Starting Antiretroviral Therapy in South Africa, Europe, or North America: A Collaborative Analysis of Prospective Studies 
PLoS Medicine  2014;11(9):e1001718.
Analyzing survival in HIV treatment cohorts, Andrew Boulle and colleagues find mortality rates in South Africa comparable to or better than those in North America by 4 years after starting antiretroviral therapy.
Please see later in the article for the Editors' Summary
Background
High early mortality in patients with HIV-1 starting antiretroviral therapy (ART) in sub-Saharan Africa, compared to Europe and North America, is well documented. Longer-term comparisons between settings have been limited by poor ascertainment of mortality in high burden African settings. This study aimed to compare mortality up to four years on ART between South Africa, Europe, and North America.
Methods and Findings
Data from four South African cohorts in which patients lost to follow-up (LTF) could be linked to the national population register to determine vital status were combined with data from Europe and North America. Cumulative mortality, crude and adjusted (for characteristics at ART initiation) mortality rate ratios (relative to South Africa), and predicted mortality rates were described by region at 0–3, 3–6, 6–12, 12–24, and 24–48 months on ART for the period 2001–2010. Of the adults included (30,467 [South Africa], 29,727 [Europe], and 7,160 [North America]), 20,306 (67%), 9,961 (34%), and 824 (12%) were women. Patients began treatment with markedly more advanced disease in South Africa (median CD4 count 102, 213, and 172 cells/µl in South Africa, Europe, and North America, respectively). High early mortality after starting ART in South Africa occurred mainly in patients starting ART with CD4 count <50 cells/µl. Cumulative mortality at 4 years was 16.6%, 4.7%, and 15.3% in South Africa, Europe, and North America, respectively. Mortality was initially much lower in Europe and North America than South Africa, but the differences were reduced or reversed (North America) at longer durations on ART (adjusted rate ratios 0.46, 95% CI 0.37–0.58, and 1.62, 95% CI 1.27–2.05 between 24 and 48 months on ART comparing Europe and North America to South Africa). While bias due to under-ascertainment of mortality was minimised through death registry linkage, residual bias could still be present due to differing approaches to and frequency of linkage.
Conclusions
After accounting for under-ascertainment of mortality, with increasing duration on ART, the mortality rate on HIV treatment in South Africa declines to levels comparable to or below those described in participating North American cohorts, while substantially narrowing the differential with the European cohorts.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
AIDS has killed about 36 million people since the first recorded case of the disease in 1981, and a similar number of people (including 25 million living in sub-Saharan Africa) are currently infected with HIV, the virus that causes AIDS. HIV destroys immune system cells (including CD4 cells, a type of lymphocyte), leaving infected individuals susceptible to other serious infections. Early in the AIDS epidemic, HIV-positive people usually died within 10 years of becoming infected. In 1996, effective antiretroviral therapy (ART) became available and, for people living in high-income countries, HIV infection became a chronic condition. But ART was expensive, so HIV/AIDS remained largely untreated and fatal in resource-limited countries. Then, in 2003, the international community began to work towards achieving universal access to ART. By the end of 2012, nearly two-thirds of HIV-positive people (nearly 10 million individuals) living in low- and middle-income countries who were eligible for treatment because their CD4 cell count had fallen below 350/mm3 blood or because they had developed an AIDS-defining condition were receiving treatment.
Why Was This Study Done?
It is known that a larger proportion of HIV-positive patients starting ART die during the first year of treatment in sub-Saharan Africa than in Europe and North America. This difference arises in part because patients in resource-limited settings tend to have lower CD4 counts when they start treatment than patients in wealthy countries. However, the lack of reliable data on mortality (death) in resource-limited settings has made it hard to compare longer-term outcomes in different settings. Information on the long-term outcomes of HIV-positive patients receiving ART in resource-limited countries is needed to guide the development of appropriate health systems and treatment regimens in these settings. In this collaborative analysis of prospective cohort studies, the researchers compare mortality up to 4 years on ART in South Africa, Europe, and North America. A prospective cohort study follows a group of individuals over time to see whether differences in specific characteristics at the start of the study affect subsequent outcomes. A collaborative analysis combines individual patient data from several studies.
What Did the Researchers Do and Find?
The researchers combined data from four South Africa cohorts of HIV-positive patients starting ART included in the International Epidemiologic Databases to Evaluate AIDS South African (IeDEA-SA) collaboration with data from six North American cohorts and nine European cohorts included in the ART Cohort Collaboration (ART-CC). The South African cohorts were chosen because unusually for studies undertaken in countries in sub-Saharan Africa the vital status of patients (whether they had died) who had been lost to follow-up in these cohorts could be obtained from the national population register. Patients in South Africa began treatment with more advanced disease (indicated by a lower average CD4 count) than patients in Europe or North America. Notably, high early mortality after starting ART in South Africa occurred mainly in patients starting ART with a CD4 count below 50 cells/mm3. The cumulative mortality after 4 years of ART was 16.6%, 4.7%, and 15.3% in South Africa, Europe, and North America, respectively. After adjusting for patient characteristics at ART initiation, the mortality rate among patients beginning ART was initially lower in Europe and North American than in South Africa. However, although the adjusted mortality rate in Europe remained lower than the rate in South Africa, the rate in North America was higher than that in South Africa between 24 and 48 months on ART.
What Do These Findings Mean?
Although the linkage to national vital registration systems (databases of births and deaths) undertaken in this collaborative analysis is likely to have greatly reduced bias due to under-ascertainment of mortality, the accuracy of these findings may still be limited by differences in how this linkage was undertaken in different settings. Nevertheless, these findings suggest that mortality among HIV-infected patients receiving ART in South Africa, although initially higher than in Europe and North America, rapidly declines with increasing duration on ART and, after 4 years of treatment, approaches the rate seen in high-income settings. Intriguingly, these findings also highlight the relatively higher late mortality in North America compared to either Europe or South Africa, a result that needs to be investigated to explore the extent to which differences in mortality ascertainment, patient characteristics and comorbidities, or health systems and treatment regimens contribute to variations in outcomes among HIV-positive patients in various settings.
Additional Information
Please access these websites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001718.
This study is further discussed in a PLOS Medicine Perspective by Agnes Binagwaho and colleagues
Information is available from the US National Institute of Allergy and Infectious Diseases on HIV infection and AIDS
NAM/aidsmap provides basic information about HIV/AIDS, and summaries of recent research findings on HIV care and treatment
Information is available from Avert, an international AIDS charity, on many aspects of HIV/AIDS, including information on universal access to ART, on HIV and AIDS in sub-Saharan Africa, and on HIV and AIDS in South Africa (in English and Spanish)
The World Health Organization provides information on all aspects of HIV/AIDS (in several languages); its 2013 Consolidated guidelines on the use of antiretroviral drugs for treating and preventing HIV infections: recommendations for a public health approach are available
The 2013 UNAIDS World AIDS Day Report provides up-to-date information about the AIDS epidemic and efforts to halt it
Information about the International Epidemiologic Databases to Evaluate AIDS South African (IeDEA-SA) collaboration and about the ART Cohort Collaboration is available
Personal stories about living with HIV/AIDS are available through Avert, Nam/aidsmap, and Healthtalkonline
doi:10.1371/journal.pmed.1001718
PMCID: PMC4159124  PMID: 25203931
9.  Sex with Women Among Men Who Have Sex with Men in China: Prevalence and Sexual Practices 
AIDS Patient Care and STDs  2013;27(9):524-528.
Abstract
Men who have sex with men and women (MSMW) are a potential bridge population for transmitting HIV to heterosexual women. This study assessed key characteristics of this subgroup of men who have sex with men (MSM) in China. Of 1141 eligible MSM, 45.6% reported bisexual behaviors. Besides marriage as a strong predictor (odds ratio: 23.90, 95% confidence interval: 14.29–39.98), older age (1.12, 1.10–1.15) and lower education (or no college education) (1.98, 1.52–2.59) were also independently associated with having ever had sex with women. MSMW reported higher proportions of alcohol drinking, heterosexual/bisexual orientation, and preference for an insertive role in anal sex than men who had sex with men only; but there was no statistically significant difference between two groups in prevalence of HIV and syphilis infections and in history of sexually transmitted infections. HIV prevention intervention programs should break the bridging role of HIV transmission in MSMW population.
doi:10.1089/apc.2013.0161
PMCID: PMC3760059  PMID: 23931683
10.  Optimizing PMTCT Service Delivery in Rural North Central Nigeria: Protocol and Design for a Cluster Randomized Study 
Contemporary clinical trials  2013;36(1):187-197.
More HIV-infected women in need of services for the prevention of mother-to-child transmission of HIV (PMTCT) give birth in Nigeria than in any other nation in the world. To meet the UNAIDS/WHO goal of eliminating mother-to-child HIV transmission by 2015, multiple interventions will be required to scale up PMTCT services, especially to lower-level, rural health facilities. To address this, we are conducting a cluster-randomized controlled study to evaluate the impact and cost-effectiveness of a novel, family-focused integrated package of services for PMTCT. A systematic reassignment of patient care responsibilities coupled with the adoption of point-of-care CD4+ cell count testing could facilitate the ability of lower-cadre health providers to manage PMTCT care, including the provision and scale-up of antiretroviral therapy to pregnant women in rural settings. Additionally, as influential community members, male partners could support their partners’ uptake of and adherence to PMTCT care. We describe an innovative approach to scaling up PMTCT service provision that incorporates considerations of where and from whom women can access services (task-shifting), ease of obtaining a CD4 result (point-of-care testing), the degree of HIV service integration for HIV-infected women and their infants, and the level of family and community involvement (specifically male partner involvement). This systematic approach, if proven feasible and effective, could be scaled up in Nigeria and similar resource-limited settings as a means to accelerate progress toward eliminating mother-to-child transmission of HIV and help women with HIV infection live long, healthy lives (Trial registration: NCT01805752).
doi:10.1016/j.cct.2013.06.013
PMCID: PMC3786261  PMID: 23816493
prevention of mother-to-child HIV transmission; task shifting; male participation; point-of-care diagnostics; Nigeria; antiretroviral therapy uptake
12.  Estimating the Optimal CD4 Count for HIV-infected Persons to Start Antiretroviral Therapy 
Epidemiology (Cambridge, Mass.)  2010;21(5):698-705.
Background
Optimal timing of antiretroviral therapy in HIV-infected persons is unclear, although two recent large observational studies have improved our understanding of the best CD4 threshold for initiation. These studies compared the effect of starting HAART on mortality and mortality/AIDS between strata defined using broad ranges of CD4 counts. We sought to expand this understanding using a novel statistical approach proposed by Robins and colleagues.
Methods
Using observational data from 1034 antiretroviral-naïve HIV-infected patients from Nashville, Tennessee, we directly estimated the optimal CD4 count for initiation of HAART to maximize patient health 6, 12, 24, and 36 months after the first instance of CD4 falling below 750. We measured health using two outcome metrics, one based on CD4 counts at the end of follow-up and the other based on a published quality-of-life scale; both metrics incorporated death, AIDS-defining events, serious non-AIDS events, and CD4 at the end of follow-up if asymptomatic.
Results
The CD4-based metric estimated that to maximize health 6, 12, 24, and 36 months after study entry, HAART should be initiated within 3 months of CD4 first dropping below 495 (95% confidence interval [CI] = 468 – 522), 554 (459 – 750), 489 (427 – 750), and 509 (460 – 750), respectively. The quality-of-life-based metric produced CD4 initiation threshold estimates of 337 (95% CI = 201–442), 354 (288 – 386), 358 (294 – 750), and 475 (287 – 750) for the same time points.
Conclusions
Our results support early initiation of antiretroviral therapy, although the criterion for starting therapy depends on the choice of health outcome.
doi:10.1097/EDE.0b013e3181e97737
PMCID: PMC3086582  PMID: 20585252
13.  Mycobacterium tuberculosis Antigen 85A Induces Th-1 Immune Responses in Systemic Sarcoidosis 
Journal of clinical immunology  2007;27(4):445-454.
Sarcoidosis is a granulomatous disease of unknown etiology, characterized by a Th-1 immunophenotype. Although humoral immune responses by sarcoidosis subjects to mycobacterial proteins have been detected, mycobacterial antigens capable of inducing cellular immune responses in sarcoidosis subjects have not been reported. We used the enzyme-linked immunospot assay to assess for recognition of the Mycobacterium tuberculosis mycolyl transferase, Antigen 85A, by peripheral blood mononuclear cells from 25 sarcoidosis subjects, 22 PPD− (purified protein derivative) healthy volunteers, and 16 PPD+ healthy subjects. Reactivity to Ag85A whole protein was observed in 15 of 25 sarcoidosis subjects compared to 2 of 22 PPD− subjects (p = 0.0006, Fisher’s exact test) and to 14 of 16 PPD+ subjects (p = 0.084, Fisher’s exact test). Monoclonal antibody against HLA-DR inhibited recognition. In addition to immune recognition of Ag85A whole protein, peptide-mapping studies identified four immunogenic Ag85A peptides, which induced Th-1 immune responses in individual sarcoidosis subjects, suggesting that multiple epitopes from a mycobacterial protein may have a role in sarcoidosis immunopathogenesis.
doi:10.1007/s10875-007-9080-4
PMCID: PMC3962023  PMID: 17357846
Sarcoidosis; mycobacteria; antigen; Th-1 immunophenotype
14.  Modeling the Impact on HIV Incidence of Combination Prevention Strategies among Men Who Have Sex with Men in Beijing, China 
PLoS ONE  2014;9(3):e90985.
Objective
To project the HIV/AIDS epidemics among men who have sex with men (MSM) under different combinations of HIV testing and linkage to care (TLC) interventions including antiretroviral therapy (ART) in Beijing, China.
Design
Mathematical modeling.
Methods
Using a mathematical model to fit prevalence estimates from 2000–2010, we projected trends in HIV prevalence and incidence during 2011–2020 under five scenarios: (S1) current intervention levels by averaging 2000–2010 coverage; (S2) increased ART coverage with current TLC; (S3) increased TLC/ART coverage; (S4) increased condom use; and (S5) increased TLC/ART plus increased condom use.
Results
The basic reproduction number based upon the current level of interventions is significantly higher than 1 ( confidence interval (CI), 1.83–2.35), suggesting that the HIV epidemic will continue to increase to 2020. Compared to the 2010 prevalence of 7.8%, the projected HIV prevalence in 2020 for the five prevention scenarios will be: (S1) Current coverage: 21.4% (95% CI, 9.9–31.7%); (S2) Increased ART: 19.9% (95% CI, 9.9–28.4%); (S3) Increased TLC/ART: 14.5% (95% CI, 7.0–23.8%); (S4) Increased condom use: 13.0% (95% CI, 9.8–28.4%); and (S5) Increased TLC/ART and condom use: 8.7% (95% CI, 5.4–11.5%). HIV epidemic will continue to rise () for S1–S4 even with hyperbolic coverage in the sensitivity analysis, and is expected to decline () for S5.
Conclusion
Our transmission model suggests that Beijing MSM will have a rapidly rising HIV epidemic. Even enhanced levels of TLC/ART will not interrupt epidemic expansion, despite optimistic assumptions for coverage. Promoting condom use is a crucial component of combination interventions.
doi:10.1371/journal.pone.0090985
PMCID: PMC3953201  PMID: 24626165
15.  Self-reported Dietary Intake and Appetite Predict Early Treatment Outcome among Low Body Mass Index Adults Initiating HIV Treatment in sub-Saharan Africa 
Public health nutrition  2012;16(3):549-558.
Objective
Low body mass index (BMI) is a major risk factor for early mortality among HIV infected persons starting antiretrovial therapy (ART) in sub-Saharan Africa, and the common patient belief that antiretroviral medications produce distressing levels of hunger is a barrier to treatment adherence. We assessed relationships between appetite, dietary intake, and treatment outcome 12 weeks after ART initiation among HIV infected adults with advanced malnutrition and immunosuppression.
Design
A prospective, observational cohort study. Dietary intake was assessed using a 24-hour recall survey. The relationships of appetite, intake, and treatment outcome were analyzed using time-varying Cox models.
Setting
A public-sector HIV clinic in Lusaka, Zambia.
Subjects
142 HIV-infected adults starting ART with BMI <16 kg/m2 and/or CD4+ lymphocyte count <50 cells/µl.
Results
Median age, BMI, and CD4+ lymphocyte count were 32 years, 16 kg/m2, and 34 cells/µL, respectively. Twenty-five participants (18%) died before 12 weeks, and another 33 (23%) were lost to care. A 500 kJ/day higher energy intake at any time after ART initiation was associated with an approximate 16% reduction in the hazard of death (AHR 0.84; p=0.01), but the relative contribution of carbohydrate, protein, and fat to total energy was not a significant predictor of outcome. Appetite normalized gradually among survivors, and hunger was rarely reported.
Conclusions
Poor early ART outcomes were strikingly high in a cohort of HIV-infected adults with advanced malnutrition, and mortality was predicted by lower dietary intake. Intervention trials to promote post-ART intake in this population may benefit survival and are warranted.
doi:10.1017/S1368980012002960
PMCID: PMC3772135  PMID: 22691872
HIV; malnutrition; antiretroviral therapy; Africa
16.  Risk Factors for Delayed Initiation of Combination Antiretroviral Therapy in Rural North central Nigeria 
Background
Timely initiation of combination antiretroviral therapy (ART) in eligible HIV-infected patients is associated with substantial reductions in mortality and morbidity. Nigeria has the second largest number of persons living with HIV/AIDS in the world. We examined patient characteristics, time to ART initiation, retention and mortality at five rural facilities in Kwara and Niger states of Nigeria.
Methods
We analyzed program-level cohort data for HIV-infected, ART-naïve clients (≥15 years) enrolled from June 2009-February 2011. We modeled the probability of ART initiation among clients meeting national ART eligibility criteria using logistic regression with splines.
Results
We enrolled 1,948 ART-naïve adults/adolescents into care, of whom 1174 were ART eligible (62% female). Only 74% of eligible patients (n=869) initiated ART within 90 days post-enrollment. The median CD4+ count for eligible clients was 156 cells/μL [IQR: 81–257], with 67% in WHO stage III/IV disease. Adjusting for CD4+ count, WHO stage, functional status, hemoglobin, body mass index, sex, age, education, marital status, employment, clinic of attendance, and month of enrollment, we found that immunosuppression (CD4 350 vs. 200, odds ratio (OR)=2.10 [95%CI: 1.31, 3.35], functional status (bedridden vs. working, OR=4.17 [95%CI: 1.63–10.67]), clinic of attendance (Kuta hospital vs. referent: OR=5.70 [95%CI:2.99–10.89]), and date of enrollment (December 2010 vs. June 2009: OR=2.13 [95%CI:1.19–3.81]) were associated with delayed ART initiation.
Conclusion
Delayed initiation of ART was associated with higher CD4+ counts, lower functional status, clinic of attendance, and later dates of enrollment among ART-eligible clients. Our findings provide targets for quality improvement efforts that may help reduce attrition and improve ART uptake in similar settings.
doi:10.1097/QAI.0b013e31829ceaec
PMCID: PMC3818360  PMID: 23727981
HIV/AIDS; Nigeria; antiretroviral therapy; implementation science; outcomes; PEPFAR; retention; mortality
17.  Active cocaine use is associated with lack of HIV-1 virologic suppression independent of non-adherence to antiretroviral therapy: use of a rapid screening tool during routine clinic visits 
AIDS care  2012;25(1):109-117.
Clarifying the relationship between illicit drug use and HIV-1 virologic suppression requires characterization of both illicit drug use activity and adherence to antiretroviral therapy (ART). We developed a rapid clinical questionnaire to assess prior 7-day illicit drug use and ART adherence in a cross-sectional study among 1,777 HIV-infected persons in care. Of these, 76% were male, 35% were African-American, and 8% reported injection drug use as their probable route of HIV-1 infection. Questionnaire-reported frequencies of cocaine and marijuana use within the previous 7 days were 3.3% and 12.1%, respectively. Over three quarters (77.8%) of participants were on ART, of whom 69.7% had HIV-1 virologic suppression (HIV-1 RNA<48 copies/mL). Univariate analyses revealed that compared to no use, cocaine and marijuana use were both associated with missed ART doses (P<0.01). Multivariable logistic regression analysis adjusting for non-adherence demonstrated that cocaine use was independently associated with failing to achieve virologic suppression (adjusted odds ratio (aOR), 0.46; 95% confidence interval (CI), 0.22–0.98) but marijuana use was not (aOR, 1.08; 95% CI, 0.72–1.62). This result strengthens the evidence of a direct effect of cocaine on virologic control, independent of non-adherence to ART.
doi:10.1080/09540121.2012.687814
PMCID: PMC3443534  PMID: 22670566
Drug use; cocaine; marijuana; antiretroviral therapy; HIV-1 virologic suppression
18.  Sensitivity Analysis of Per-Protocol Time-to-Event Treatment Efficacy in Randomized Clinical Trials 
Journal of the American Statistical Association  2013;108(503):10.1080/01621459.2013.786649.
Summary
Assessing per-protocol treatment effcacy on a time-to-event endpoint is a common objective of randomized clinical trials. The typical analysis uses the same method employed for the intention-to-treat analysis (e.g., standard survival analysis) applied to the subgroup meeting protocol adherence criteria. However, due to potential post-randomization selection bias, this analysis may mislead about treatment efficacy. Moreover, while there is extensive literature on methods for assessing causal treatment effects in compliers, these methods do not apply to a common class of trials where a) the primary objective compares survival curves, b) it is inconceivable to assign participants to be adherent and event-free before adherence is measured, and c) the exclusion restriction assumption fails to hold. HIV vaccine efficacy trials including the recent RV144 trial exemplify this class, because many primary endpoints (e.g., HIV infections) occur before adherence is measured, and nonadherent subjects who receive some of the planned immunizations may be partially protected. Therefore, we develop methods for assessing per-protocol treatment efficacy for this problem class, considering three causal estimands of interest. Because these estimands are not identifiable from the observable data, we develop nonparametric bounds and semiparametric sensitivity analysis methods that yield estimated ignorance and uncertainty intervals. The methods are applied to RV144.
doi:10.1080/01621459.2013.786649
PMCID: PMC3811958  PMID: 24187408
As-treated; Bounds; Causal inference; Exclusion restriction; Ignorance region; Intention to treat; Principal stratification; Selection bias; Survival analysis
19.  HIV/AIDS-Related Attitudes and Practices Among Traditional Healers in Zambézia Province, Mozambique 
Abstract
Objectives
To document HIV knowledge, treatment practices, and the willingness of traditional healers to engage with the health system in Zambézia Province, Mozambique.
Settings/location
Traditional healers offer culturally acceptable services and are more numerous in Mozambique than are allopathic providers. Late presentation of human immunodeficiency virus (HIV) infection/acquired immunodeficiency syndrome (AIDS) is reported among persons who have first sought care from traditional healers.
Design
One hundred and thirty-nine (139) traditional healers were interviewed in their native languages (Chuabo or Lomwe) in Zambézia Province. Furthermore, 24 traditional healers were observed during patient encounters. Healers answered a semistructured questionnaire regarding their knowledge of HIV/AIDS, general treatment practices, attitudes toward the allopathic health system, and their beliefs in their abilities to cure AIDS.
Results
Traditional healers were older and had less formal education than the general population. Razor cutting in order to rub herbs into bloodied skin was observed, and healers reported razor cutting as a routine practice. Healers stated that they did not refer HIV patients to clinics for two principal reasons: (1) patient symptoms/signs of HIV were unrecognized, and (2) practitioners believed they could treat the illness effectively themselves. Traditional healers were far more likely to believe in a spiritual than an infectious origin of HIV disease. Prior HIV/AIDS training was not associated with better knowledge or referral practices, though 81% of healers were interested in engaging allopathic providers.
Conclusions
It was found that the HIV-related practices of traditional healers probably increase risk for both HIV-infected and uninfected persons through delayed care and reuse of razors. Mozambican traditional healers attribute HIV pathogenesis to spiritual, not infectious, etiologies. Healers who had received prior HIV training were no more knowledgeable, nor did they have better practices. The willingness expressed by 4 in 5 healers to engage local formal health providers in HIV/AIDS care suggests a productive way forward, though educational efforts must be effective and income concerns considered.
doi:10.1089/acm.2011.0682
PMCID: PMC3513988  PMID: 23171035
20.  Heterogeneity in outcomes of treated HIV-positive patients in Europe and North America: relation with patient and cohort characteristics 
Background HIV cohort collaborations, which pool data from diverse patient cohorts, have provided key insights into outcomes of antiretroviral therapy (ART). However, the extent of, and reasons for, between-cohort heterogeneity in rates of AIDS and mortality are unclear.
Methods We obtained data on adult HIV-positive patients who started ART from 1998 without a previous AIDS diagnosis from 17 cohorts in North America and Europe. Patients were followed up from 1 month to 2 years after starting ART. We examined between-cohort heterogeneity in crude and adjusted (age, sex, HIV transmission risk, year, CD4 count and HIV-1 RNA at start of ART) rates of AIDS and mortality using random-effects meta-analysis and meta-regression.
Results During 61 520 person-years, 754/38 706 (1.9%) patients died and 1890 (4.9%) progressed to AIDS. Between-cohort variance in mortality rates was reduced from 0.84 to 0.24 (0.73 to 0.28 for AIDS rates) after adjustment for patient characteristics. Adjusted mortality rates were inversely associated with cohorts’ estimated completeness of death ascertainment [excellent: 96–100%, good: 90–95%, average: 75–89%; mortality rate ratio 0.66 (95% confidence interval 0.46–0.94) per category]. Mortality rate ratios comparing Europe with North America were 0.42 (0.31–0.57) before and 0.47 (0.30–0.73) after adjusting for completeness of ascertainment.
Conclusions Heterogeneity between settings in outcomes of HIV treatment has implications for collaborative analyses, policy and clinical care. Estimated mortality rates may require adjustment for completeness of ascertainment. Higher mortality rate in North American, compared with European, cohorts was not fully explained by completeness of ascertainment and may be because of the inclusion of more socially marginalized patients with higher mortality risk.
doi:10.1093/ije/dys164
PMCID: PMC3535877  PMID: 23148105
HIV; AIDS; antiretroviral therapy; mortality; cohort; heterogeneity; prognostic model; socio-economic status
21.  Using Audit Information to Adjust Parameter Estimates for Data Errors in Clinical Trials 
Background
Audits are often performed to assess the quality of clinical trial data, but beyond detecting fraud or sloppiness, the audit data is generally ignored. In earlier work using data from a non-randomized study, Shepherd and Yu (2011) developed statistical methods to incorporate audit results into study estimates, and demonstrated that audit data could be used to eliminate bias.
Purpose
In this manuscript we examine the usefulness of audit-based error-correction methods in clinical trial settings where a continuous outcome is of primary interest.
Methods
We demonstrate the bias of multiple linear regression estimates in general settings with an outcome that may have errors and a set of covariates for which some may have errors and others, including treatment assignment, are recorded correctly for all subjects. We study this bias under different assumptions including independence between treatment assignment, covariates, and data errors (conceivable in a double-blinded randomized trial) and independence between treatment assignment and covariates but not data errors (possible in an unblinded randomized trial). We review moment-based estimators to incorporate the audit data and propose new multiple imputation estimators. The performance of estimators is studied in simulations.
Results
When treatment is randomized and unrelated to data errors, estimates of the treatment effect using the original error-prone data (i.e., ignoring the audit results) are unbiased. In this setting, both moment and multiple imputation estimators incorporating audit data are more variable than standard analyses using the original data. In contrast, in settings where treatment is randomized but correlated with data errors and in settings where treatment is not randomized, standard treatment effect estimates will be biased. And in all settings, parameter estimates for the original, error-prone covariates will be biased. Treatment and covariate effect estimates can be corrected by incorporating audit data using either the multiple imputation or moment-based approaches. Bias, precision, and coverage of confidence intervals improve as the audit size increases.
Limitations
The extent of bias and the performance of methods depend on the extent and nature of the error as well as the size of the audit. This work only considers methods for the linear model. Settings much different than those considered here need further study.
Conclusions
In randomized trials with continuous outcomes and treatment assignment independent of data errors, standard analyses of treatment effects will be unbiased and are recommended. However, if treatment assignment is correlated with data errors or other covariates, naive analyses may be biased. In these settings, and when covariate effects are of interest, approaches for incorporating audit results should be considered.
doi:10.1177/1740774512450100
PMCID: PMC3728661  PMID: 22848072
audit; bias; clinical trials; measurement error; multiple imputation
22.  Utilization of Cervical Cancer Screening Services and Trends in Screening Positivity Rates in a ‘Screen-And-Treat’ Program Integrated with HIV/AIDS Care in Zambia 
PLoS ONE  2013;8(9):e74607.
Background
In the absence of stand-alone infrastructures for delivering cervical cancer screening services, efforts are underway in sub-Saharan Africa to dovetail screening with ongoing vertical health initiatives like HIV/AIDS care programs. Yet, evidence demonstrating the utilization of cervical cancer prevention services in such integrated programs by women of the general population is lacking.
Methods
We analyzed program operations data from the Cervical Cancer Prevention Program in Zambia (CCPPZ), the largest public sector programs of its kind in sub-Saharan Africa. We evaluated patterns of utilization of screening services by HIV serostatus, examined contemporaneous trends in screening outcomes, and used multivariable modeling to identify factors associated with screening test positivity.
Results
Between January 2006 and April 2011, CCPPZ services were utilized by 56,247 women who underwent cervical cancer screening with visual inspection with acetic acid (VIA), aided by digital cervicography. The proportion of women accessing these services who were HIV-seropositive declined from 54% to 23% between 2006–2010, which coincided with increasing proportions of HIV-seronegative women (from 22% to 38%) and women whose HIV serostatus was unknown (from 24% to 39%) (all p-for trend<0.001). The rates of VIA screening positivity declined from 47% to 17% during the same period (p-for trend <0.001), and this decline was consistent across all HIV serostatus categories. After adjusting for demographic and sexual/reproductive factors, HIV-seropositive women were more than twice as likely (Odds ratio 2.62, 95% CI 2.49, 2.76) to screen VIA-positive than HIV-seronegative women.
Conclusions
This is the first ‘real world’ demonstration in a public sector implementation program in a sub-Saharan African setting that with successful program scale-up efforts, nurse-led cervical cancer screening programs targeting women with HIV can expand and serve all women, regardless of HIV serostatus. Screening program performance can improve with adequate emphasis on training, quality control, and telemedicine-support for nurse-providers in clinical decision making.
doi:10.1371/journal.pone.0074607
PMCID: PMC3776830  PMID: 24058599
23.  Duration of Anti-Tuberculosis Therapy and Timing of Antiretroviral Therapy Initiation: Association with Mortality in HIV-Related Tuberculosis 
PLoS ONE  2013;8(9):e74057.
Background
Antiretroviral therapy (ART) decreases mortality risk in HIV-infected tuberculosis patients, but the effect of the duration of anti-tuberculosis therapy and timing of anti-tuberculosis therapy initiation in relation to ART initiation on mortality, is unclear.
Methods
We conducted a retrospective observational multi-center cohort study among HIV-infected persons concomitantly treated with Rifamycin-based anti-tuberculosis therapy and ART in Latin America. The study population included persons for whom 6 months of anti-tuberculosis therapy is recommended.
Results
Of 253 patients who met inclusion criteria, median CD4+ lymphocyte count at ART initiation was 64 cells/mm3, 171 (68%) received >180 days of anti-tuberculosis therapy, 168 (66%) initiated anti-tuberculosis therapy before ART, and 43 (17%) died. In a multivariate Cox proportional hazards model that adjusted for CD4+ lymphocytes and HIV-1 RNA, tuberculosis diagnosed after ART initiation was associated with an increased risk of death compared to tuberculosis diagnosis before ART initiation (HR 2.40; 95% CI 1.15, 5.02; P = 0.02). In a separate model among patients surviving >6 months after tuberculosis diagnosis, after adjusting for CD4+ lymphocytes, HIV-1 RNA, and timing of ART initiation relative to tuberculosis diagnosis, receipt of >6 months of anti-tuberculosis therapy was associated with a decreased risk of death (HR 0.23; 95% CI 0.08, 0.66; P=0.007).
Conclusions
The increased risk of death among persons diagnosed with tuberculosis after ART initiation highlights the importance of screening for tuberculosis before ART initiation. The decreased risk of death among persons receiving > 6 months of anti-tuberculosis therapy suggests that current anti-tuberculosis treatment duration guidelines should be re-evaluated.
doi:10.1371/journal.pone.0074057
PMCID: PMC3774609  PMID: 24066096
24.  Risk Factors for Symptomatic Hyperlactatemia and Lactic Acidosis Among Combination Antiretroviral Therapy-Treated Adults in Botswana: Results from a Clinical Trial 
Abstract
Nucleoside analogue reverse transcriptase inhibitors are an integral component of combination antiretroviral treatment regimens. However, their ability to inhibit polymerase-γ has been associated with several mitochondrial toxicities, including potentially life-threatening lactic acidosis. A total of 650 antiretroviral-naive adults (69% female) initiated combination antiretroviral therapy (cART) and were intensively screened for toxicities including lactic acidosis as part of a 3-year clinical trial in Botswana. Patients were categorized as no lactic acidosis symptoms, minor symptoms but lactate <4.4 mmol/liter, and symptoms with lactate ≥4.4 mmol/liter [moderate to severe symptomatic hyperlactatemia (SH) or lactic acidosis (LA)]. Of 650 participants 111 (17.1%) developed symptoms and/or laboratory results suggestive of lactic acidosis and had a serum lactate drawn; 97 (87.4%) of these were female. There were 20 events, 13 having SH and 7 with LA; all 20 (100%) were female (p<0.001). Cox proportional hazard analysis limited to the 451 females revealed that having a higher baseline BMI was predictive for the development of SH/LA [aHR=1.17 per one-unit increase (1.08–1.25), p<0.0001]. Ordered logistic regression performed among all 650 patients revealed that having a lower baseline hemoglobin [aOR=1.28 per one-unit decrease (1.1–1.49), p=0.002] and being randomized to d4T/3TC-based cART [aOR=1.76 relative to ZDV/3TC (1.03–3.01), p=0.04] were predictive of the symptoms and/or the development of SH/LA. cART-treated women in sub-Saharan Africa, especially those having higher body mass indices, should receive additional monitoring for SH/LA. Women presently receiving d4T/3TC-based cART in such settings also warrant more intensive monitoring.
doi:10.1089/aid.2011.0303
PMCID: PMC3399551  PMID: 22540188
25.  A new residual for ordinal outcomes 
Biometrika  2012;99(2):473-480.
We propose a new residual for regression models of ordinal outcomes, defined as E{sign(y,Y)}, where y is the observed outcome and Y is a random variable from the fitted distribution. This new residual is a single value per subject irrespective of the number of categories of the ordinal outcome, contains directional information between the observed value and the fitted distribution, and does not require the assignment of arbitrary numbers to categories. We study its properties, describe its connections with other residuals, ranks and ridits, and demonstrate its use in model diagnostics.
doi:10.1093/biomet/asr073
PMCID: PMC3635659  PMID: 23843667
Model diagnostics; Ordinal outcome; Ordinal regression; Residual

Results 1-25 (67)