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1.  Predictors of the number of under-five malnourished children in Bangladesh: application of the generalized poisson regression model 
BMC Public Health  2013;13:11.
Background
Malnutrition is one of the principal causes of child mortality in developing countries including Bangladesh. According to our knowledge, most of the available studies, that addressed the issue of malnutrition among under-five children, considered the categorical (dichotomous/polychotomous) outcome variables and applied logistic regression (binary/multinomial) to find their predictors. In this study malnutrition variable (i.e. outcome) is defined as the number of under-five malnourished children in a family, which is a non-negative count variable. The purposes of the study are (i) to demonstrate the applicability of the generalized Poisson regression (GPR) model as an alternative of other statistical methods and (ii) to find some predictors of this outcome variable.
Methods
The data is extracted from the Bangladesh Demographic and Health Survey (BDHS) 2007. Briefly, this survey employs a nationally representative sample which is based on a two-stage stratified sample of households. A total of 4,460 under-five children is analysed using various statistical techniques namely Chi-square test and GPR model.
Results
The GPR model (as compared to the standard Poisson regression and negative Binomial regression) is found to be justified to study the above-mentioned outcome variable because of its under-dispersion (variance < mean) property. Our study also identify several significant predictors of the outcome variable namely mother’s education, father’s education, wealth index, sanitation status, source of drinking water, and total number of children ever born to a woman.
Conclusions
Consistencies of our findings in light of many other studies suggest that the GPR model is an ideal alternative of other statistical models to analyse the number of under-five malnourished children in a family. Strategies based on significant predictors may improve the nutritional status of children in Bangladesh.
doi:10.1186/1471-2458-13-11
PMCID: PMC3599578  PMID: 23297699
Malnutrition; Under-five children; Predictors; Generalized Poisson regression model; Bangladesh
2.  An updated prostate cancer staging nomogram (Partin tables) based on cases from 2006 to 2011 
BJU international  2012;111(1):10.1111/j.1464-410X.2012.11324.x.
Objective
To update the 2007 Partin tables in a contemporary patient population.
Patients and Methods
The study population consisted of 5,629 consecutive men who underwent RP and staging lymphadenectomy at the Johns Hopkins Hospital between January 1, 2006 and July 30, 2011 and met inclusion criteria.
Polychotomous logistic regression analysis was used to predict the probability of each pathologic stage category: organ-confined disease (OC), extraprostatic extension (EPE), seminal vesicle involvement (SV+), or lymph node involvement (LN+) based on preoperative criteria.
Preoperative variables included biopsy Gleason score (6, 3+4, 4+3, 8, and 9–10), serum PSA (0–2.5, 2.6–4.0, 4.1–6.0, 6.1–10.0, greater than 10.0 ng/mL), and clinical stage (T1c, T2c, and T2b/T2c).
Bootstrap re-sampling with 1000 replications was performed to estimate 95% confidence intervals for predicted probabilities of each pathologic state.
Results
The median PSA was 4.9 ng/mL, 63% had Gleason 6 disease, and 78% of men had T1c disease.
73% of patients had OC disease, 23% had EPE, 3% had SV+ but not LN+, and 1% had LN+ disease. Compared to the previous Partin nomogram, there was no change in the distribution of pathologic state.
The risk of LN+ disease was significantly higher for tumours with biopsy Gleason 9–10 than Gleason 8 (O.R. 3.2, 95% CI 1.3–7.6).
The c-indexes for EPE vs. OC, SV+ vs. OC, and LN+ vs. OC were 0.702, 0.853, and 0.917, respectively.
Men with biopsy Gleason 4+3 and Gleason 8 had similar predicted probabilities for all pathologic stages.
Most men presenting with Gleason 6 disease or Gleason 3+4 disease have <2% risk of harboring LN+ disease and may have lymphadenectomy omitted at RP.
Conclusions
The distribution of pathologic stages did not change at our institution between 2000–2005 and 2006–2011.
The updated Partin nomogram takes into account the updated Gleason scoring system and may be more accurate for contemporary patients diagnosed with prostate cancer.
doi:10.1111/j.1464-410X.2012.11324.x
PMCID: PMC3876476  PMID: 22834909
prostate cancer; prostatectomy; prostage-specific antigen; nomograms; staging
3.  Considering health insurance: how do dialysis initiates with Medicaid coverage differ from persons without Medicaid coverage? 
Background. Type of health insurance is an important mediator of medical outcomes in the United States. Medicaid, a jointly sponsored Federal/State programme, is designed to serve medically needy individuals. How these patients differ from non-Medicaid-enrolled incident dialysis patients and how these differences have changed over time have not been systematically examined.
Methods. Using data from the United States Renal Data System, we identified individuals initiating dialysis from 1995 to 2004 and categorized their health insurance status. Longitudinal trends in demographic, risk behaviour, functional, comorbidity, laboratory and dialysis modality factors, as reported on the Medical Evidence Form (CMS-2728), were examined in all insurance groups. Polychotomous logistic regression was used to estimate adjusted generalized ratios (AGRs) for these factors by insurance status, with Medicaid as the referent insurance group.
Results. Overall, males constitute a growing percentage of both Medicaid and non-Medicaid patients, but in contrast to other insurance groups, Medicaid has a higher proportion of females. Non-Caucasians also constitute a higher proportion of Medicaid patients than non-Medicaid patients. Body mass index increased in all groups over time, and all groups witnessed a significant decrease in initiation on peritoneal dialysis. Polychotomous regression showed generally lower AGRs for minorities, risk behaviours and functional status, and higher AGRs for males, employment and self-care dialysis, for non-Medicaid insurance relative to Medicaid.
Conclusions. While many broad parallel trends are evident in both Medicaid and non-Medicaid incident dialysis patients, many important differences between these groups exist. These findings could have important implications for policy planners, providers and payers.
doi:10.1093/ndt/gfp396
PMCID: PMC2910325  PMID: 19736241
demographics; dialysis; end-stage renal disease; insurance; Medicaid
4.  Can early closure and restenosis after endoluminal stenting be predicted from clinical, procedural, and angiographic variables at the time of intervention? 
British Heart Journal  1995;74(6):592-597.
OBJECTIVES--To develop a statistical model to assess the risk of early closure and restenosis on the basis of the information available at the time of stent implantation. DESIGN--An exploratory forward, stepwise multivariate logistic regression for each adverse event and multivariate polychotomous analysis for both events. SETTING--Tertiary referral centre for interventional treatment of coronary artery disease. PATIENTS--243 consecutive, successful stenting procedures between 1986 and 1993 with the Wallstent, the Palmaz-Schatz and Wiktor stents with analysis of clinical, procedural, and angiographic variables. MEAN OUTCOME MEASURES--Early closure was defined as angiographically documented stent thrombosis within the first 3 weeks after implantation and restenosis according to the 50% reference diameter reduction criterion. RESULTS--Overall early closure and restenosis rates were 14.4% (35/243) and 19.2% (40/208, for a 97% repeat angiography rate). The statistical model predicted a worse outcome for male patients, with less restenosis in female patients. The only risk factor in female patients was the presence of collaterals to the target lesion. For male patients the following risk factors for closure and restenosis were retained: multiple stent implantation during the same session, the presence of collaterals to the target lesion, stenting of the left anterior descending artery or of the left circumflex artery, and bailout stenting. Only bailout stenting implied a decreased restenosis risk. CONCLUSIONS--Clinical, procedural and angiographic variables increase the risk for early closure and restenosis after endoluminal stenting. The prediction models described above need to be validated prospectively.
PMCID: PMC484111  PMID: 8541161
5.  Correlates of D-dimer in older persons 
Background and aims
D-dimer is a marker of active fibrinolysis. Understanding how age-related factors affect D-dimer levels may help the interpretation of high D-dimer levels in older individuals.
Methods
776 Baltimore Longitudinal Study on Aging (BLSA) participants (mean age 68.4±13.9 yrs) were divided into three groups according to baseline D-dimer levels >200 ng/mL; 100–200 ng/mL and <100 ng/mL.
Results
D-dimer level increased with age (p<0.0001). Using polychotomous logistic regression models, we found that age, cholesterol, triglycerides, creatinine, erythrocyte sedimentation rate, hemoglobin and body mass index were independently associated with D-dimer level.
Conclusions
Rising levels of D-dimer with age can be explained in part by the high prevalence of pro-inflammatory conditions and increasing burden of lipid abnormalities, anemia and obesity. These factors compromise the specificity of D-dimer levels as a diagnostic aid to thrombosis in older individuals.
PMCID: PMC2863304  PMID: 20305364
D-dimer; inflammation; obesity
6.  Fruit, Vegetable, and Animal Food Intake and Breast Cancer Risk by Hormone Receptor Status 
Nutrition and cancer  2012;64(6):806-819.
Background
The effects of diet on breast cancer are controversial and whether the effects vary with hormone receptor status has not been well investigated. This study evaluated the associations of dietary factors with risk for breast cancer overall and by hormone receptor status of tumors among Chinese women.
Methods
The Shanghai Breast Cancer Study, a large, population-based, case-control study, enrolled 3,443 cases and 3,474 controls in 1996–1998 (phase I) and 2002–2004 (phase II); 2,676 cases had ER and PR data. Dietary intake was assessed using a validated, quantitative, food frequency questionnaire (FFQ). Odds ratios (ORs) and 95% confidence intervals (95% CI) were derived from multivariate, polychotomous, unconditional logistic regression models.
Results
Total vegetable intake was inversely related to breast cancer risk, with an adjusted OR for the highest quintile of 0.80 (95% CI = 0.67–0.95; P trend=0.02). Reduced risk was also related to high intake of allium vegetables (P trend = 0.01) and fresh legumes (P trend = 0.0008). High intake of citrus fruits and rosaceae fruits were inversely associated with breast cancer risk (P trend = 0.003 and P trend = 0.004, respectively), although no consistent association was seen for total fruit intake. Elevated risk was observed for all types of meat and fish intake (all P trend <0.05), while intakes of eggs and milk were associated with a decreased risk of breast cancer (both P trend <0.05). There was little evidence that associations with dietary intakes varied across the four tumor subtypes or between ER+/PR+ and ER−/PR− tumors (P for heterogeneity >0.05).
Conclusion
Our results suggest that high intake of total vegetables, certain fruits, milk, and eggs may reduce the risk of breast cancer, while high consumption of animal-source foods may increase risk. The dietary associations did not appear to vary by ER/PR status.
doi:10.1080/01635581.2012.707277
PMCID: PMC3758811  PMID: 22860889
7.  Haplotype-Based Regression Analysis and Inference of Case–Control Studies with Unphased Genotypes and Measurement Errors in Environmental Exposures 
Biometrics  2007;64(3):673-684.
Summary. It is widely believed that risks of many complex diseases are determined by genetic susceptibilities, environmental exposures, and their interaction. Chatterjee and Carroll (2005, Biometrika 92, 399–418) developed an efficient retrospective maximum-likelihood method for analysis of case–control studies that exploits an assumption of gene–environment independence and leaves the distribution of the environmental covariates to be completely nonparametric. Spinka, Carroll, and Chatterjee (2005, Genetic Epidemiology 29, 108–127) extended this approach to studies where certain types of genetic information, such as haplotype phases, may be missing on some subjects. We further extend this approach to situations when some of the environmental exposures are measured with error. Using a polychotomous logistic regression model, we allow disease status to have K + 1 levels. We propose use of a pseudolikelihood and a related EM algorithm for parameter estimation. We prove consistency and derive the resulting asymptotic covariance matrix of parameter estimates when the variance of the measurement error is known and when it is estimated using replications. Inferences with measurement error corrections are complicated by the fact that the Wald test often behaves poorly in the presence of large amounts of measurement error. The likelihood-ratio (LR) techniques are known to be a good alternative. However, the LR tests are not technically correct in this setting because the likelihood function is based on an incorrect model, i.e., a prospective model in a retrospective sampling scheme. We corrected standard asymptotic results to account for the fact that the LR test is based on a likelihood-type function. The performance of the proposed method is illustrated using simulation studies emphasizing the case when genetic information is in the form of haplotypes and missing data arises from haplotype-phase ambiguity. An application of our method is illustrated using a population-based case–control study of the association between calcium intake and the risk of colorectal adenoma.
doi:10.1111/j.1541-0420.2007.00930.x
PMCID: PMC2672569  PMID: 18047538
EM algorithm; Errors in variables; Gene-environment independence; Gene-environment interactions; Likelihood-ratio tests in misspecified models; Inferences in measurement error models; Profile likelihood; Semiparametric methods
8.  Determinants of dental user groups among an elderly, low-income population. 
Health Services Research  1996;30(6):809-825.
OBJECTIVE: We test whether or not there are differences for selected variables among five dental user groups and one nondental group within an elderly, low-income population. DATA SOURCE: We used ten years of Medicare Part B claims data from the Cincinnati Health Department for all clinic users 62 years of age and older who participated in the Municipal Health Services Program. STUDY DESIGN: A polychotomous logistic regression model determined the ability to differentiate between the groups for each of the selected variables, controlling for race. Next, a polychotomous stepwise logistic regression was used in finding a multivariate model for determining dental user group membership. Logistic regression was used to ascertain which variables were discriminators between any two types of dental users. PRINCIPAL FINDINGS: Mean number of medical visits, mean number of prescriptions filled, and race are determinants of group membership, with the nondental group having more medical visits and more likely to be white. Although year of birth cohort is statistically significant in determining dental user types, the direction of effect is not constant across the comparisons. However, the relative risk for being in the two complete denture groups, compared to both compliant subgroups, increases with each older cohort. CONCLUSIONS: Higher levels of medical use may "crowd out" dental use, even when it is without user cost, either because the medical problems are treated as a higher priority, or because dealing with medical needs leaves too little perceived time or energy to seek dental care. Even in a low-income population seeking dental care, there appears to be a birth cohort effect with a decline in the younger elderly who require two complete dentures.
PMCID: PMC1070094  PMID: 8591931
9.  Organochlorine residues in human breast milk: analysis through a sentinel practice network. 
STUDY OBJECTIVE--The study aimed to assess through a sentinel practice network the validity of data on levels of organochlorine residues in human milk along with personal, lifestyle, and exposure variables of breastfeeding women; to compare the results of this new approach with those of the Lower Saxony breast milk surveillance programme; and to test hypotheses on potential determinants of contamination levels. DESIGN--Eligible women were enrolled into this cross sectional study by a network of 51 paediatric practices when bringing their babies for a U3 infant screening examination (4th to 6th week after delivery). Lifestyle and exposure factors were obtained by questionnaire. All milk samples were analysed for hexachlorocyclohexane, hexachlorbenzole, DDT, dieldrin, polychlorinated biphenyls (PCB) and heptachlor; half the samples were also analysed for dioxin. Analytic statistics were computed using polychotomous logistic regression (PLR). SETTING--The study was conducted in Lower Saxony, Germany, from summer 1992 to summer 1993. PARTICIPANTS--Altogether 156 primiparous, breast feeding German women, aged 25-35 years, who had been born and had grown up in West Germany, were studied. MAIN RESULTS--Compared with the regular programme, participants in this study had their milk analysed sooner after delivery and were more likely to have grown up in rural areas, less likely to have been exposed to hazardous substances, less likely to have a diet of health food, and slightly less likely to be a smoker at the time of the study. Breast milk contamination levels were comparable in both studies, and in all but two cases well below the tolerable concentrations established by the Deutsche Forschungsgemeinschaft (German Research Fellowship). After adjustment for potential confounders using polychotomous logistic regression, there were statistically significant positive associations between breast milk contamination and age (PCB, test for trend: p = 0.006), average dietary fat intake per week (dioxin, p = 0.01), and proximity of residence to hazardous sites (dioxin, p < 0.05), and negative associations between residue levels and relative body weight at the time of the study (PCB; p < 0.0001) and difference in body weight (weight minus weight before the pregnancy; PCB, p = 0.0002), respectively. CONCLUSIONS--Sentinel practice networks are a feasible and low-biased approach to population based breast milk studies. The contamination levels and associations found are biologically plausible and comparable with the results of other studies. To reduce organochlorine residue levels in human milk in the short term, breast-feeding women should be advised not to try to reduce their weight until after lactation. Public promotion of a lower dietary fat intake may reduce the lifetime accumulation of organochlorine compounds in the human body fat tissue in the long term, resulting in lower concentrations in breast milk as well.
PMCID: PMC1060863  PMID: 7561664
10.  Level of oral health impacts among patients participating in PEARL: a dental practice-based research network 
Objectives
To determine whether participants of a dental practice-based research network (PBRN) differ in their level of oral health impact as measured by the Oral Health Impact Profile (OHIP) questionnaire.
Methods
A total of 2410 patients contributed 2432 OHIP measurements (median age = 43 years; interquartile range = 28) were enrolled in four dental studies. All participants completed the Oral Health Impact Profile (OHIP-14) during a baseline visit. The main outcome of the current study was the level of oral health impact, defined as follows: no impact (“Never” reported on all items); low (“Occasionally” or “Hardly ever” as the greatest frequency score reported on any item); and high (“Fairly often” or “Very often” as the greatest frequency reported on any item). Polychotomous logistic regression was used to develop a predictive model for the level of oral health impact considering the following predictors: patient’s age, gender, race, practice location, type of dentist, and number of years the enrolling dentist has been practicing.
Results
A high level of oral health impacts was reported in 8% of the sample; almost a third (29%) of the sample reported a low level of impacts, and 63% had no oral health impacts. The prevalence of impacts differed significantly across protocols (P<0.001). Females were more likely to be in the high oral impact group than the no impact group compared to males (OR=1.46; 95% CI= 1.06–1.99). African-Americans were more likely to report high oral impacts when compared to other racial/ethnic groups (OR=2.11; 95% CI = 1.26–3.55). Protective effects for being in the high or in the low impact groups were observed among patients enrolled by a solo practice (P<0.001) or by more experienced dentists (P=0.01). A small but highly significant statistical association was obtained for patient age (P<0.001). In the multivariate model, patient’s age, practice size and gender were found to jointly be significant predictors of oral health impact level.
Conclusions
Patients’ subjective report of oral health impact in the clinical setting is of importance for their health. In the context of a dental PBRN, the report of oral health-related quality of life (OHRQoL) was different across four dental studies. The observed findings validate the differential impact that oral health has on the patients’ perception of OHRQoL particularly among specific groups. Similar investigations to elucidate the factors associated with patient’s report of quality of life are warranted.
doi:10.1111/j.1600-0528.2012.00676.x
PMCID: PMC3380181  PMID: 22390788
Oral-Health Impact; OHRQoL; Dental PBRN; OHIP-14; Patient Reported Outcomes; Subjective Health
11.  Do Christian Denominations Exhibit Higher Rates of Alcohol Consumption? A Study of Korean American Women in California 
Journal of Religion and Health  2011;52(1):285-298.
Although Korean American women show high levels of involvement in religious practices and high prevalence of alcohol consumption, no studies have assessed the association between religious denomination and alcohol intake among this group of women. This cross-sectional study examined the associations of religious denomination and religious commitment to alcohol consumption among Korean American women in California. Polychotomous regression models were used to provide estimates of the associations between religious denomination and religious commitment to alcohol consumption. Catholic Korean American women (OR 5.61 P < 0.01) and Independent Christian women (OR 4.87 P < 0.01) showed stronger associations to heavy alcohol consumption when compared to Conservative Christian Korean American women. Path analysis suggested that specific denominations had both direct and indirect effects on the outcome of interest, and that religious commitment and drinking models served as moderators for this phenomenon.
doi:10.1007/s10943-011-9471-y
PMCID: PMC3560953  PMID: 21286816
Religious denomination; Korean American women; Alcohol consumption; Polychotomous regression; Drinking models; Path analysis
12.  Accuracy of Body Mass Index Categories Based on Self-Reported Height and Weight Among Women in the United States 
Maternal and child health journal  2008;13(4):489-496.
Objective
The purpose of this study was to assess the accuracy of BMI categories based on self-reported height and weight in adult women.
Methods
BMI categories from self-reported responses were compared to categories measured during physical examination from women, age 18 or older, who participated in the National Health and Examination Survey, 1999-2004. We first examined strength of agreement using Cohen’s kappa, which, unlike sensitivity and specificity, allows for the comparison of polychotomous measures beyond chance agreement. Kappa regression identifies potential threats to accuracy. Likelihood of bias, as measured by under-reporting, was examined using logistic regression.
Results
Cohen’s kappa estimates were 0.443 for pregnant women (N = 724) and 0.705 for non-pregnant women (N = 5,910). Kappa varied by age and race, but was largely unrelated to socioeconomic status, health and health behaviors. Women who visited a physician in the last year or been diagnosed with osteoporosis were more accurate, while women most likely to under-report were older, white, non-Hispanic, and college-educated.
Conclusions
Our results suggest substantial agreement between self-reported and measured categories, except for women who are pregnant, above the age of 75 or without physician visits. Under-reporting may be more prevalent in well-educated, white populations than minority populations.
doi:10.1007/s10995-008-0384-7
PMCID: PMC2731685  PMID: 18607705
Obesity; Body mass index; Cohen’s kappa
13.  Psychological Factors Affecting Alcohol Use after Spinal Cord Injury 
Spinal cord  2010;49(5):637-642.
Objective
The purpose of this study is to assess risk factors, including personality and socioeconomic indicators, with alcohol use among persons with spinal cord injury.
Study Design
Cross-sectional
Setting
A large rehabilitation hospital in the southeastern United States
Methods
1,549 participants responded to a survey on outcomes after SCI. We used polychotomous logistic regression to assess the relationships of personality and socioeconomic factors with alcohol use.
Results
In this study population, 19.3% were heavy drinkers, 29.4% moderate, and 51.7% abstinent. Annual household income and education were both associated with heavy alcohol use, with persons with higher income or education more likely to be heavy drinkers. Impulsive sensation seeking, neuroticism/anxiety, and aggression/hostility were associated with increased odds of heavy drinking.
Conclusion
This study adds to the body of evidence indicating a substantial portion of individuals with SCI are heavy drinkers, and that personality and socioeconomic status are associated with heavy drinking.
doi:10.1038/sc.2010.160
PMCID: PMC3090503  PMID: 21102575
Spinal Cord Injuries; Alcohol Drinking; Personality; Socioeconomic Factors
14.  Mammographic Breast Density and Subsequent Risk of Breast Cancer in Postmenopausal Women According to Tumor Characteristics 
Background
Few studies that investigated the associations between breast density and subsequent breast cancer according to tumor characteristics have produced inconclusive findings. We aimed to determine whether the associations between breast density and subsequent breast cancer varied by tumor characteristics.
Methods
We included 1042 postmenopausal women diagnosed with breast cancer between June 1, 1989, and June 30, 2004, and 1794 matched control subjects from the Nurses’ Health Study, an ongoing prospective cohort study of 121 701 registered female nurses across the United States. Breast density was estimated from digitized images using computerized techniques. Information on breast cancer risk factors was obtained prospectively from biennial questionnaires before the date of cancer diagnosis for case subjects and matched control subjects. Polychotomous logistic regression was used to assess associations of breast density with tumor subtypes based on invasiveness, histology, size, grade, receptor status, and involvement of lymph nodes. All tests of statistical significance were two-sided.
Results
The risk of breast cancer increased progressively with increase in percent breast density (Ptrend < .001). Women with higher breast density (≥50%) showed a 3.39-fold (odds ratio = 3.39, 95% confidence interval = 2.46 to 4.68) increased risk of breast cancer compared with women with lower breast density (<10%). The associations between breast density and breast cancer risk were stronger for in situ compared with invasive tumors (Pheterogeneity < .01), high-grade compared with low-grade tumors (Pheterogeneity = .02), larger (>2 cm) compared with smaller (≤2 cm) tumors (Pheterogeneity < .01), and estrogen receptor–negative compared with estrogen receptor–positive tumors (Pheterogeneity = .04). There were no differences in associations by tumor histology, involvement of lymph nodes, and progesterone receptor and HER2 status (Pheterogeneity > .05).
Conclusions
The findings suggest that higher mammographic density is associated with more aggressive tumor characteristics and also with in situ tumors.
doi:10.1093/jnci/djr225
PMCID: PMC3149043  PMID: 21795664
15.  Basic statistics for clinicians: 4. Correlation and regression. 
Correlation and regression help us to understand the relation between variables and to predict patients' status in regard to a particular variable of interest. Correlation examines the strength of the relation between two variables, neither of which is considered the variable one is trying to predict (the target variable). Regression analysis examines the ability of one or more factors, called independent variables, to predict a patient's status in regard to the target or dependent variable. Independent and dependent variables may be continuous (taking a wide range of values) or binary (dichotomous, yielding yes-or-no results). Regression models can be used to construct clinical prediction rules that help to guide clinical decisions. In considering regression and correlation, clinicians should pay more attention to the magnitude of the correlation or the predictive power of the regression than to whether the relation is statistically significant.
PMCID: PMC1337703  PMID: 7859197
16.  Regression Calibration for Dichotomized Mismeasured Predictors* 
Epidemiologic research focuses on estimating exposure-disease associations. In some applications the exposure may be dichotomized, for instance when threshold levels of the exposure are of primary public health interest (e.g., consuming 5 or more fruits and vegetables per day may reduce cancer risk). Errors in exposure variables are known to yield biased regression coefficients in exposure-disease models. Methods for bias-correction with continuous mismeasured exposures have been extensively discussed, and are often based on validation substudies, where the “true” and imprecise exposures are observed on a small subsample. In this paper, we focus on biases associated with dichotomization of a mismeasured continuous exposure. The amount of bias, in relation to measurement error in the imprecise continuous predictor, and choice of dichotomization cut point are discussed. Measurement error correction via regression calibration is developed for this scenario, and compared to naïvely using the dichotomized mismeasured predictor in linear exposure-disease models. Properties of the measurement error correction method (i.e., bias, mean-squared error) are assessed via simulations.
doi:10.2202/1557-4679.1143
PMCID: PMC2743435  PMID: 20046953
measurement error correction; dichotomizing covariates; regression calibration
17.  Prognostic significance of peripheral monocyte count in patients with extranodal natural killer/T-cell lymphoma 
BMC Cancer  2013;13:222.
Background
Extranodal natural killer/T-cell lymphoma (ENKL) has heterogeneous clinical manifestations and prognosis. This study aims to evaluate the prognostic impact of absolute monocyte count (AMC) in ENKL, and provide some immunologically relevant information for better risk stratification in patients with ENKL.
Methods
Retrospective data from 163 patients newly diagnosed with ENKL were analyzed. The absolute monocyte count (AMC) at diagnosis was analyzed as continuous and dichotomized variables. Independent prognostic factors of survival were determined by Cox regression analysis.
Results
The AMC at diagnosis were related to overall survival (OS) and progression-free survival (PFS) in patients with ENKL. Multivariate analysis identified AMC as independent prognostic factors of survival, independent of International Prognostic Index (IPI) and Korean prognostic index (KPI). The prognostic index incorporating AMC and absolute lymphocyte count (ALC), another surrogate factor of immune status, could be used to stratify all 163 patients with ENKL into different prognostic groups. For patients who received chemotherapy followed by radiotherapy (102 cases), the three AMC/ALC index categories identified patients with significantly different survivals. When superimposed on IPI or KPI categories, the AMC/ALC index was better able to identify high-risk patients in the low-risk IPI or KPI category.
Conclusion
The baseline peripheral monocyte count is shown to be an effective prognostic indicator of survival in ENKL patients. The prognostic index related to tumor microenvironment might be helpful to identify high-risk patients with ENKL.
doi:10.1186/1471-2407-13-222
PMCID: PMC3653743  PMID: 23638998
Absolute monocyte count; Extranodal natural killer/T-cell lymphoma; Prognosis; Tumor microenvironment
18.  Prognostic Model for Predicting Survival of Patients With Metastatic Urothelial Cancer Treated With Cisplatin-Based Chemotherapy 
A prognostic model that predicts overall survival (OS) for metastatic urothelial cancer (MetUC) patients treated with cisplatin-based chemotherapy was developed, validated, and compared with a commonly used Memorial Sloan-Kettering Cancer Center (MSKCC) risk-score model. Data from 7 protocols that enrolled 308 patients with MetUC were pooled. An external multi-institutional dataset was used to validate the model. The primary measurement of predictive discrimination was Harrell’s c-index, computed with 95% confidence interval (CI). The final model included four pretreatment variables to predict OS: visceral metastases, albumin, performance status, and hemoglobin. The Harrell’s c-index was 0.67 for the four-variable model and 0.64 for the MSKCC risk-score model, with a prediction improvement for OS (the U statistic and its standard deviation were used to calculate the two-sided P = .002). In the validation cohort, the c-indices for the four-variable and the MSKCC risk-score models were 0.63 (95% CI = 0.56 to 0.69) and 0.58 (95% CI = 0.52 to 0.65), respectively, with superiority of the four-variable model compared with the MSKCC risk-score model for OS (the U statistic and its standard deviation were used to calculate the two-sided P = .02).
doi:10.1093/jnci/djt015
PMCID: PMC3691944  PMID: 23411591
19.  Preferences for Sites of Care Among Urban Homeless and Housed Poor Adults 
OBJECTIVE
To describe sources of health care used by homeless and housed poor adults.
DESIGN
In a cross-sectional survey, face-to-face interviews were conducted to assess source of usual care, preferred site of care for specific problems, perceived need for health insurance at different sites of care, and satisfaction with care received. Polychotomous logistic regression analysis was used to identify the factors associated with selecting non-ambulatory-care sites for usual care.
SETTING
Twenty-four community-based sites (i.e., soup kitchens, drop-in centers, and emergency shelters) frequented by the homeless and housed poor in Allegheny County, Pa.
PARTICIPANTS
Of the 388 survey respondents, 85.6% were male, 78.1% African American, 76.9% between 30 and 49 years of age, 59.3% were homeless less than 1 year, and 70.6% had health insurance.
MAIN RESULTS
Overall, 350 (90.2%) of the respondents were able to identify a source of usual medical care. Of those, 51.3% identified traditional ambulatory care sites (i.e., hospital-based clinics, community and VA clinics, and private physicians offices); 28.9% chose emergency departments; 8.0%, clinics based in shelters or drop-in centers; and 2.1%, other sites. Factors associated with identifying nonambulatory sites for usual care included lack of health insurance (relative risk range for all sites [RR] =3.1–4.0), homelessness for more than 2 years (RR =1.4–3.0), receiving no medical care in the previous 6 months (RR =1.6–7.5), nonveteran status (RR =1.0–2.5), being unmarried (RR =1.2–3.1), and white race (RR =1.0–3.3).
CONCLUSIONS
Having no health insurance or need for care in the past 6 months increased the use of a non-ambulatory-care site as a place for usual care. Programs designed to decrease emergency department use may need to be directed at those not currently accessing any care.
doi:10.1046/j.1525-1497.1999.09258.x
PMCID: PMC1496749  PMID: 10571704
homeless; health service utilization; emergency department care; preferences for care
20.  HIV–Tuberculosis Coinfection in Southern California: Evaluating Disparities in Disease Burden 
American journal of public health  2010;100(Suppl 1):S178-S185.
Objectives
We sought to understand tuberculosis (TB) and HIV coinfection trends in San Diego County, California, and to identify associations between sociodemographic risk factors and TB and HIV coinfection.
Methods
We analyzed TB surveillance data from 1993 through 2007. TB cases were grouped by HIV status: positive, negative, or unknown. We used Poisson regression to estimate trends and tested associations between TB and HIV coinfection and sociodemographic risk factors with polychotomous logistic regression.
Results
Of 5172 TB cases, 8.8% were also infected with HIV. Incidence of coinfected cases did not change significantly over the period studied, but the proportion of cases among Hispanics increased significantly, whereas cases among non-Hispanic Whites and Blacks decreased. TB cases with HIV coinfection were significantly more likely to be Hispanic, male, injection drugs users, and aged 30 to 49 years, relative to cases with TB disease only.
Conclusions
The burden of TB and HIV in San Diego has shifted to Hispanics in the last decade. To address this health disparity, binational TB and HIV prevention efforts are needed.
doi:10.2105/AJPH.2009.170142
PMCID: PMC2837460  PMID: 20147681
21.  Demographic and occupational predictors of early response to a mailed invitation to enroll in a longitudinal health study 
Background
Often in survey research, subsets of the population invited to complete the survey do not respond in a timely manner and valuable resources are expended in recontact efforts. Various methods of improving response have been offered, such as reducing questionnaire length, offering incentives, and utilizing reminders; however, these methods can be costly. Utilizing characteristics of early responders (refusal or consent) in enrollment and recontact efforts may be a unique and cost-effective approach for improving the quality of epidemiologic research.
Methods
To better understand early responders of any kind, we compared the characteristics of individuals who explicitly refused, consented, or did not respond within 2 months from the start of enrollment into a large cohort study of US military personnel. A multivariate polychotomous logistic regression model was used to estimate the effect of each covariate on the odds of early refusal and on the odds of early consent versus late/non-response, while simultaneously adjusting for all other variables in the model.
Results
From regression analyses, we found many similarities between early refusers and early consenters. Factors associated with both early refusal and early consent included older age, higher education, White race/ethnicity, Reserve/Guard affiliation, and certain information technology and support occupations.
Conclusion
These data suggest that early refusers may differ from late/non-responders, and that certain characteristics are associated with both early refusal and early consent to participate. Structured recruitment efforts that utilize these differences may achieve early response, thereby reducing mail costs and the use of valuable resources in subsequent contact efforts.
doi:10.1186/1471-2288-7-6
PMCID: PMC1794255  PMID: 17397558
22.  Perceived Race-Based Discrimination, Employment Status, and Job Stress in a National Sample of Black Women: Implications for Health Outcomes 
Previous research has not systematically examined the relationship of perceived race-based discriminations to labor force participation or job related stresses–problems experienced by Black women. The present study investigated the relative contributions of perceived race-based discriminations and sociodemographic characteristics to employment status and job stress in a national probability sample (the National Survey of Black Americans; J. S. Jackson, 1991) of Black women in the United States. Logit and polychotomous logistic regression analyses revealed that Black women’s current employment status was best explained by sociodemographic measures. In contrast, the combination of perceived discrimination and sociodemographics differentially affects patterns of employment status and perceived job stress in the work environment of Black women. Implications of these findings for the health of African American women are discussed.
PMCID: PMC3681822  PMID: 9547054
23.  Comparison of Scoring Methods for ACE-27: Simpler Is Better 
Journal of geriatric oncology  2012;3(3):238-245.
Objective
To examine the prognostic value of different comorbidity coding schemes for predicting survival of newly diagnosed elderly cancer patients.
Materials and Methods
We analyzed data from 8,867 patients aged 65 years of age or older, newly diagnosed with cancer. Comorbidities present at the time of diagnosis were collected using the Adult Comorbidity Evaluation-27 index (ACE-27). We examined multiple scoring schemes based on the individual comorbidity ailments, and their severity rating. Harrell’s c index and Akaike Information Criterion (AIC) were used to evaluate the performance of the different comorbidity models.
Results
Comorbidity led to an increase in c index from 0.771 for the base model to 0.782 for a model that included indicator variables for every ailment. The prognostic value was however much higher for prostate and breast cancer patients. A simple model which considered linear scores from 0 to 3 per ailment, controlling for cancer type, was optimal according to AIC.
Conclusion
The presence of comorbidity impacts on the survival of elderly cancer patients, especially for less lethal cancers, such as prostate and breast cancers. Different ailments have different impacts on survival, necessitating the use of different weights per ailment in a simple summary score of the ACE-27.
doi:10.1016/j.jgo.2012.01.006
PMCID: PMC3375822  PMID: 22712031
Comorbidity; comorbid ailment; elderly; cancer patients; prognostic; survival
24.  Dietary intake and breast density in high-risk women: a cross-sectional study 
Background
Women with a family history of breast cancer may be at higher risk for breast cancer, but few previous studies evaluating diet and breast cancer have focused on such women. The objective of the present study was to determine whether diet, a modifiable risk factor, is related to breast density among women at high genetic risk for breast cancer.
Methods
Women with at least one first-degree or second-degree relative with breast cancer or ovarian cancer participating in the Fox Chase Cancer Center Family Risk Assessment Program completed health history and food frequency questionnaires and received standard screening mammograms. Cranial–caudal mammographic images were classified into the four Breast Imaging Reporting and Data System categories ranging from 'entirely fatty' to 'extremely dense'. Logistic regression analysis using proportional odds models for polychotomous outcomes provided estimates of odds ratios for having a higher category versus a lower category of breast density.
Results
Among 157 high-risk women, breast density was inversely associated with vitamin D intake (odds ratio for third tertile versus first tertile, 0.5; 95% confidence interval, 0.2–1.0). In contrast, intakes above the median level for protein (odds ratio, 3.0; 95% confidence interval, 1.3–6.9) and above the median level for animal protein (odds ratio, 4.3; 95% confidence interval, 1.8–10.3) were associated with higher breast density, but only among women whose family history did not reflect a known familial cancer syndrome or a breast cancer predisposition gene.
Conclusion
For women with a strong family history that was not associated with known cancer syndromes, dietary factors may be associated with breast density, a strong predictor of breast cancer risk. Since women with strong family history are often very motivated to change their lifestyle habits, further studies are needed to confirm whether changes in diet will change the breast density and the subsequent onset of breast cancer in these women.
doi:10.1186/bcr1781
PMCID: PMC2242670  PMID: 17949495
25.  Use of Four Biomarkers to Evaluate the Risk of Breast Cancer Subtypes in the Women’s Contraceptive and Reproductive Experiences Study 
Cancer research  2010;70(2):575-587.
Epidemiological studies have suggested that some hormone-related breast cancer risk factors differentially influence risk of breast cancer subtypes defined by estrogen receptor (ER) and progesterone receptor (PR) expression status in tumor tissue. However, it remains unclear whether human epidermal growth factor receptor-2 (HER2) and p53 protein (p53) expression status in tumor tissue further differentiate these exposure-risk-group associations. We evaluated the associations of oral contraceptive (OC) use and reproductive factors with incident invasive breast cancer subtypes among 1197 population-based cases and 2015 controls from the Los Angeles County or Detroit components of the Women’s Contraceptive and Reproductive Experiences Study. We used multivariable polychotomous unconditional logistic regression methods to conduct case-control comparisons by ER/PR/HER2/p53 status. We found that OC use was not associated with any breast cancer subtype defined by ER/PR/HER2/p53, except for a 2.9-fold increased risk for triple negative (ER−/PR−/HER2−) tumors among older women (ages 45–64 years) who started OC use before age 18. Parity was associated with decreased risk of luminal A (ER+ or PR+, HER2−), luminal B (ER+ or PR+, HER2+), and ER−/PR−/HER2+ tumors. Age at first full-term pregnancy was positively associated with luminal A tumors among older women. Neither of these reproductive factors was associated with triple negative tumors. Long duration of breastfeeding lowered risk of triple negative and luminal A tumors. No further differential risk patterns were noted when p53 was also considered. These results provide evidence supporting a difference in some hormone-related risk factor profiles between triple negative and other breast cancer subtypes defined by ER/PR/HER2.
doi:10.1158/0008-5472.CAN-09-3460
PMCID: PMC2807992  PMID: 20068186
ER/PR/HER2/p53; breast cancer; hormone-related factors; oral contraceptive; reproductive factors

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