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1.  Adjusting for dependent comorbidity in the calculation of healthy life expectancy 
Healthy life expectancy – sometimes called health-adjusted life expectancy (HALE) – is a form of health expectancy indicator that extends measures of life expectancy to account for the distribution of health states in the population. The World Health Organization has estimated healthy life expectancy for 192 WHO Member States using information from health interview surveys and from the Global Burden of Disease Study. The latter estimates loss of health by cause, age and sex for populations. Summation of prevalent years lived with disability (PYLD) across all causes would result in overestimation of the severity of the population average health state because of comorbidity between conditions. Earlier HALE calculations made adjustments for independent comorbidity in adding PYLD across causes. This paper presents a method for adjusting for dependent comorbidity using available empirical data.
Data from five large national health surveys were analysed by age and sex to estimate "dependent comorbidity" factors for pairs of conditions. These factors were defined as the ratio of the prevalence of people with both conditions to the product of the two total prevalences for each of the conditions. The resulting dependent comorbidity factors were used for all Member States to adjust for dependent comorbidity in summation of PYLD across all causes and in the calculation of HALE. A sensitivity analysis was also carried out for order effects in the proposed calculation method.
There was surprising consistency in the dependent comorbidity factors across the five surveys. The improved estimation of dependent comorbidity resulted in reductions in total PYLD per capita ranging from a few per cent in younger adult ages to around 8% in the oldest age group (80 years and over) in developed countries and up to 15% in the oldest age group in the least developed countries. The effect of the dependent comorbidity adjustment on estimated healthy life expectancies is small for some regions (high income countries, Eastern Europe, Western Pacific) and ranges from an increase of 0.5 to 1.5 years for countries in Latin America, South East Asia and Sub-Saharan Africa.
The available evidence suggests that dependent comorbidity is important, and that adjustment for it makes a significant difference to resulting HALE estimates for some regions of the world. Given the data limitations, we recommend a normative adjustment based on the available evidence, and applied consistently across all countries.
PMCID: PMC1484491  PMID: 16620383
2.  Estimating health-adjusted life expectancy conditional on risk factors: results for smoking and obesity 
Smoking and obesity are risk factors causing a large burden of disease. To help formulate and prioritize among smoking and obesity prevention activities, estimations of health-adjusted life expectancy (HALE) for cohorts that differ solely in their lifestyle (e.g. smoking vs. non smoking) can provide valuable information. Furthermore, in combination with estimates of life expectancy (LE), it can be tested whether prevention of obesity and smoking results in compression of morbidity.
Using a dynamic population model that calculates the incidence of chronic disease conditional on epidemiological risk factors, we estimated LE and HALE at age 20 for a cohort of smokers with a normal weight (BMI < 25), a cohort of non-smoking obese people (BMI>30) and a cohort of 'healthy living' people (i.e. non smoking with a BMI < 25). Health state valuations for the different cohorts were calculated using the estimated disease prevalence rates in combination with data from the Dutch Burden of Disease study. Health state valuations are multiplied with life years to estimate HALE. Absolute compression of morbidity is defined as a reduction in unhealthy life expectancy (LE-HALE) and relative compression as a reduction in the proportion of life lived in good health (LE-HALE)/LE.
Estimates of HALE are highest for a 'healthy living' cohort (54.8 years for men and 55.4 years for women at age 20). Differences in HALE compared to 'healthy living' men at age 20 are 7.8 and 4.6 for respectively smoking and obese men. Differences in HALE compared to 'healthy living' women at age 20 are 6.0 and 4.5 for respectively smoking and obese women. Unhealthy life expectancy is about equal for all cohorts, meaning that successful prevention would not result in absolute compression of morbidity. Sensitivity analyses demonstrate that although estimates of LE and HALE are sensitive to changes in disease epidemiology, differences in LE and HALE between the different cohorts are fairly robust. In most cases, elimination of smoking or obesity does not result in absolute compression of morbidity but slightly increases the part of life lived in good health.
Differences in HALE between smoking, obese and 'healthy living' cohorts are substantial and similar to differences in LE. However, our results do not indicate that substantial compression of morbidity is to be expected as a result of successful smoking or obesity prevention.
PMCID: PMC1636666  PMID: 17083719
3.  Impact of diabetes mellitus on life expectancy and health-adjusted life expectancy in Canada 
The objectives of this study were to estimate life expectancy (LE) and health-adjusted life expectancy (HALE) for Canadians with and without diabetes and to evaluate the impact of diabetes on population health using administrative and survey data.
Mortality data from the Canadian Chronic Disease Surveillance System (2004 to 2006) and Health Utilities Index data from the Canadian Community Health Survey (2000 to 2005) were used. Life table analysis was applied to calculate LE, HALE, and their confidence intervals using the Chiang and the adapted Sullivan methods.
LE and HALE were significantly lower among people with diabetes than for people without the disease. LE and HALE for females without diabetes were 85.0 and 73.3 years, respectively (males: 80.2 and 70.9 years). Diabetes was associated with a loss of LE and HALE of 6.0 years and 5.8 years, respectively, for females, and 5.0 years and 5.3 years, respectively, for males, living with diabetes at 55 years of age. The overall gains in LE and HALE after the hypothetical elimination of prevalent diagnosed diabetes cases in the population were 1.4 years and 1.2 years, respectively, for females, and 1.3 years for both LE and HALE for males.
The results of the study confirm that diabetes is an important disease burden in Canada impacting the female and male populations differently. The methods can be used to calculate LE and HALE for other chronic conditions, providing useful information for public health researchers and policymakers.
PMCID: PMC3787852  PMID: 22531113
Life expectancy; Health-adjusted life expectancy; Diabetes mellitus; Health utilities index; Summary measure of population health
4.  Self-rated health as a tool for estimating health-adjusted life expectancy among patients newly diagnosed with localized prostate cancer: A preliminary study 
Localized prostate cancer (LPC) patients are faced with numerous treatment options, including observation or watchful waiting. The choice of treatment largely depends on their baseline health-adjusted life expectancy (HALE). By consensus, physicians recommend treatment if the patient’s HALE is ten or more years. However, the estimation of HALE is difficult. Although subjective by nature, self-rated health (SRH) is a robust predictor of mortality. We studied the usefulness of SRH in estimating HALE in patients who are considering treatment for LPC.
A total of 144 LPC patients from a large urology private practice in Norfolk, Virginia, were surveyed before they had chosen a treatment option.
HALE determined by SRH correlated well with objective health measures, and was higher than age-based life expectancy by an average of 2 years. The observed difference in life expectancy due to SRH adjustment was higher among patients with a better socioeconomic and health profile.
SRH is an easy-to-use indicator of HALE in LPC patients. A table for HALE estimation by age and SRH is provided for men aged 70-80 years. Additional research with larger samples and prospective study designs are needed before the SRH method can be used in primary care and urology settings.
PMCID: PMC3066264  PMID: 21132389
Localized Prostate Cancer; Life Expectancy; Self-rated Health; Urology
5.  Comparing life expectancy and health-adjusted life expectancy by body mass index category in adult Canadians: a descriptive study 
While many studies have examined differences between body mass index (BMI) categories in terms of mortality risk and health-related quality of life (HRQL), little is known about the effect of body weight on health expectancy. We examined life expectancy (LE), health-adjusted life expectancy (HALE), and proportion of LE spent in nonoptimal (or poor) health by BMI category for the Canadian adult population (age ≥ 20).
Respondents to the National Population Health Survey (NPHS) were followed for mortality outcomes from 1994 to 2009. Our study population at baseline (n=12,478) was 20 to 100 years old with an average age of 47. LE was produced by building abridged life tables by sex and BMI category using data from the NPHS and the Canadian Chronic Disease Surveillance System. HALE was estimated using the Health Utilities Index from the Canadian Community Health Survey as a measure of HRQL. The contribution of HRQL to loss of healthy life years for each BMI category was also assessed using two methods: by calculating differences between LE and HALE proportional to LE and by using a decomposition technique to separate out mortality and HRQL contributions to loss of HALE.
At age 20, for both sexes, LE is significantly lower in the underweight and obesity class 2+ categories, but significantly higher in the overweight category when compared to normal weight (obesity class 1 was nonsignificant). HALE at age 20 follows these same associations and is significantly lower for class 1 obesity in women. Proportion of life spent in nonoptimal health and decomposition of HALE demonstrate progressively higher losses of healthy life associated with lowered HRQL for BMI categories in excess of normal weight.
Although being in the overweight category for adults may be associated with a gain in life expectancy as compared to normal weight adults, overweight individuals also experience a higher proportion of these years of life in poorer health. Due to the descriptive nature of this study, further research is needed to explore the causal mechanisms which explain these results, including the important differences we observed between sexes and within obesity subcategories.
PMCID: PMC3842774  PMID: 24252500
Overweight; Obesity; Underweight; Body mass index; Life expectancy; Health expectancy; Mortality; Health-related quality of life
6.  Using linked data to calculate summary measures of population health: Health-adjusted life expectancy of people with Diabetes Mellitus 
To estimate the health-adjusted life expectancy (HALE) from diabetes mellitus (DM) using a population health survey linked to a population-based DM registry.
The 1996/97 Ontario Health Survey (N = 35,517) was linked to the Ontario Diabetes Database (N = 487,576). The Health Utilities Index (HUI3) was used to estimate health-related quality of life. HALE was estimated using an adapted Sullivan method.
Life expectancy at birth of people with DM was 64.7 and 70.7 years for men and women – 12.8 and 12.2 years less than for men and women without DM. The HUI3 was lower for physician-diagnosed DM compared to self-reported DM (0.799 versus 0.872). HALE at birth was 58.3 and 62.8 years for men and women – 11.9 and 10.7 years less than that of men and women without DM.
The linked data approach demonstrates that DM is an important cause of disease burden. This approach reduces assumptions when estimating the prevalence and severity of disability from DM compared to methods that rely on self-reported disease status or indirect assessment of disability severity.
PMCID: PMC406424  PMID: 15038828
7.  The effect of comorbidity on health-related quality of life for injury patients in the first year following injury: comparison of three comorbidity adjustment approaches 
Three approaches exist to deal with the impact of comorbidity in burden of disease studies - the maximum limit approach, the additive approach, and the multiplicative approach. The aim of this study was to compare the three comorbidity approaches in patients with temporary injury consequences as well as comorbid chronic conditions with nontrivial health impacts.
Disability weights were assessed using data from the EQ-5D instrument developed by the EuroQol Group and derived from a postal survey among 2,295 injury patients at 2.5 and 9 months after being treated at an emergency department. We compared the observed and predicted EQ-5D disability weights in comorbid cases using data from injury patients with and without comorbidity who were restored from their injuries at 9 months follow-up. The predicted disability weights were calculated using the maximum limit approach, additive approach, and multiplicative approach. The intraclass correlation coefficient (ICC) was used to test whether the values of the observed disability weights and the three model-predicted disability weights were correlated.
The EQ-5D disability weight of injury patients increased significantly with the number of comorbid diseases. The ICCs of the additive, multiplicative, and maximum limit models were 0.817, 0.778, and 0.674, respectively. Although the 95% confidence intervals of the ICCs of the three models overlap, the maximum limit model seems to fit less well than the additive and multiplicative models. For mild to moderate chronic disease (disability weight below 0.21), the association between predicted and observed disability weights was low.
Comorbidity has a high impact on disability measured with EQ-5D. Ignoring the effect of comorbidity restricts the use of the burden of disease concept in multimorbid populations. Gains from health care or interventions may be easily overestimated if a substantial number of patients suffer from additional conditions. The results of this study found that in accounting for comorbidity effects, all three models showed a strong association between the predicted and observed morbid disability weight, though the maximum limit model seems to fit less well than the additive and multiplicative models. The three models do not fit well in the case of mild to moderate pre-existing disease.
PMCID: PMC3096905  PMID: 21513572
8.  The burden of disease and injury in Iran 2003 
The objective of this study was to estimate the burden of disease and injury in Iran for the year 2003, using Disability-Adjusted Life Years (DALYs) at the national level and for six selected provinces.
Methods developed by the World Health Organization for National Burden of Disease (NBD) studies were applied to estimate disease and injury incidence for the calculation of Years of Life Lost due to premature mortality (YLL), Years Lived with Disability (YLD), and DALYs. The following adjustments of the NBD methodology were made in this study: a revised list with 213 disease and injury causes, development of new and more specific disease modeling templates for cancers and injuries, and adjustment for dependent comorbidity. We compared the results with World Health Organization (WHO) estimates for Eastern Mediterranean Region, sub-region B in 2002.
We estimated that in the year 2003, there were 21,572 DALYs due to all diseases and injuries per 100,000 Iranian people of all ages and both sexes. From this total number of DALYs, 62% were due to disability premature deaths (YLD) and 38% were due to premature deaths (YLL); 58% were due to noncommunicable diseases, 28% – to injuries, and 14% – to communicable, maternal, perinatal, and nutritional conditions. Fifty-three percent of the total number of 14.349 million DALYs in Iran were in males, with 36.5% of the total due to intentional and unintentional injuries, 15% due to mental and behavioral disorders, and 10% due to circulatory system diseases; and 47% of DALYs were in females, with 18% of the total due to mental and behavioral disorders, 18% due to intentional and unintentional injuries, and 12% due to circulatory system diseases. The disease and injury causes leading to the highest number of DALYs in males were road traffic accidents (1.071 million), natural disasters (548 thousand), opioid use (510 thousand), and ischemic heart disease (434 thousand). The leading causes of DALYs in females were ischemic heart disease (438 thousand), major depressive disorder (420 thousand), natural disasters (419 thousand), and road traffic accidents (235 thousand). The burden of disease at the province level showed marked variability. DALY estimates by Iran's NBD study were higher than those for EMR-B by WHO.
The health and disease profile in Iran has made the transition from the dominance of communicable diseases to that of noncommunicable diseases and road traffic injuries. NBD results are to be used in health program planning, research, and resource allocation and generation policies and practices.
PMCID: PMC2711041  PMID: 19527516
9.  Global patterns of healthy life expectancy in the year 2002 
BMC Public Health  2004;4:66.
Healthy life expectancy – sometimes called health-adjusted life expectancy (HALE) – is a form of health expectancy indicator that extends measures of life expectancy to account for the distribution of health states in the population. The World Health Organization reports on healthy life expectancy for 192 WHO Member States. This paper describes variation in average levels of population health across these countries and by sex for the year 2002.
Mortality was analysed for 192 countries and disability from 135 causes assessed for 17 regions of the world. Health surveys in 61 countries were analyzed using new methods to improve the comparability of self-report data.
Healthy life expectancy at birth ranged from 40 years for males in Africa to over 70 years for females in developed countries in 2002. The equivalent "lost" healthy years ranged from 15% of total life expectancy at birth in Africa to 8–9% in developed countries.
People living in poor countries not only face lower life expectancies than those in richer countries but also live a higher proportion of their lives in poor health.
PMCID: PMC547900  PMID: 15619327
10.  Comorbidity and disease burden in the National Comorbidity Survey Replication (NCS-R) 
Depression and anxiety  2012;29(9):797-806.
Disease burden estimates rarely consider comorbidity. Using a recently developed methodology for integrating information about comorbidity into disease burden estimates, we examined the comparative burdens of 9 mental and 10 chronic physical disorders in the National Comorbidity Survey Replication (NCS-R).
Face-to-face interviews in a national household sample (n = 5,692) assessed associations of disorders with scores on a visual analog scale (VAS) of perceived health. Multiple regression analysis with interactions for comorbidity was used to estimate these associations. Simulation was used to estimate incremental disorder-specific effects adjusting for comorbidity.
74.9% of respondents reported one or more disorders. 73.8–98.2% of respondents with disorders reported having at least one other disorder. The best-fitting model to predict VAS scores included disorder main effects and interactions for number of disorders. Adjustment for comorbidity reduced individual-level disorder-specific burden estimates substantially, but with considerable between-disorder variation (.07–.69 ratios of disorder-specific estimates with and without adjustment for comorbidity). Four of the five most burdensome disorders at the individual level were mental disorders based on bivariate analyses (panic/agoraphobia, bipolar disorder, PTSD, major depression) but only two based on multivariate analyses, adjusting for comorbidity (panic/agoraphobia, major depression). Neurological disorders, chronic pain conditions, and diabetes were the other most burdensome individual-level disorders. Chronic pain conditions, cardiovascular disorders, arthritis, insomnia, and major depression were the most burdensome societal-level disorders.
Adjustments for comorbidity substantially influence estimates of disease burden, especially those of mental disorders, underlining the importance of including information about comorbidity in studies of mental disorders.
PMCID: PMC4005614  PMID: 22585578
bias; burden of illness; confounding factors; cost of illness; epidemiology; global burden of disease; health valuation; visual analog scale (VAS)
11.  The societal gain of medical development and innovation in gastroenterology 
Gastroenterology has over the past 30 years evolved very rapidly. The societal benefits to which this has led are incompletely determined, yet form a mandate to determine the need for future innovations and further development of the field. A more thorough understanding of societal benefits may help to determine future goals and improve decision making.
The objective of this article is to determine the societal gains of medical innovations in the field of gastroenterology in the past and future, using peptic ulcer disease as an example of past innovation and the implementation of colorectal cancer screening as an illustration of future gains.
Literature searches were performed for data on peptic ulcer and colorectal cancer epidemiology, treatment outcomes, and costs. National and governmental databases in the Netherlands were searched to obtain the input for calculations of quality-adjusted life years (QALYs), health-adjusted life expectancy (HALE), and the corresponding societal benefit.
Since 1980 the improvements in peptic ulcer treatment have had a limited impact on life expectancy, rising from 83.6 years to 83.7 years, but have led to a yearly gain of 46,000 QALYs, caused by improved quality of life. These developments in the field of peptic ulcer translated into a yearly gain of 1.8 billion to 7.8 billion euros in 2008 compared with the 1980s.
Mortality due to colorectal cancer is high, with 21.6 deaths per 100,000 per year in the Netherlands (European Standardized Rate (ESR)). The future implementation of a nationwide call-recall colorectal cancer screening by means of biennial fecal immunochemical testing (FIT) is expected to result in a 50%–80% mortality reduction and thus a gain of an estimated 35,000 life years per year, corresponding to 26,000 QALYs per year. The effects of the implementation of FIT screening can be translated to a future societal gain of 1.0 billion to 4.4 billion euro.
The innovations and developments in the field of gastroenterology have led to significant societal gains in the past three decades. This process will continue in the near future as a result of further developments. These calculations provide a template for calculations on the need for specialist training as well as research and implementation of new developments in our field.
PMCID: PMC4040771  PMID: 24917981
Peptic ulcer; colon cancer; screening; societal gain; quality of life
12.  Health-Adjusted Life Expectancy among Canadian Adults with and without Hypertension 
Hypertension can lead to cardiovascular diseases and other chronic conditions. While the impact of hypertension on premature death and life expectancy has been published, the impact on health-adjusted life expectancy has not, and constitutes the research objective of this study. Health-adjusted life expectancy (HALE) is the number of expected years of life equivalent to years lived in full health. Data were obtained from the Canadian Chronic Disease Surveillance System (mortality data 2004–2006) and the Canadian Community Health Survey (Health Utilities Index data 2000–2005) for people with and without hypertension. Life table analysis was applied to calculate life expectancy and health-adjusted life expectancy and their confidence intervals. Our results show that for Canadians 20 years of age, without hypertension, life expectancy is 65.4 years and 61.0 years, for females and males, respectively. HALE is 55.0 years and 52.8 years for the two sexes at age 20; and 24.7 years and 22.9 years at age 55. For Canadians with hypertension, HALE is only 48.9 years and 47.1 years for the two sexes at age 20; and 22.7 years and 20.2 years at age 55. Hypertension is associated with a significant loss in health-adjusted life expectancy compared to life expectancy.
PMCID: PMC3123912  PMID: 21738858
13.  Burden of disease due to cancer in Spain 
BMC Public Health  2009;9:42.
Burden of disease is a joint measure of mortality and morbidity which makes it easier to compare health problems in which these two components enjoy different degrees of relative importance. The objective of this study is ascertaining the burden of disease due to cancer in Spain via the calculation of disability-adjusted life years (DALYs).
DALYs are the sum of years of life lost due to premature mortality and years lost due to disability. World Health Organization methodology and the following sources of data were used: the Mortality Register and Princeton Model Life Table for Years of life lost due to premature mortality and population, incidence estimates (Spanish tumour registries and fitting of generalized linear mixed models), duration (from data of survival in Spain from the EUROCARE-3 study and fitting of Weibull distribution function) and disability (weights published in the literature) for Years lost due to disability.
There were 828,997 DALYs due to cancer (20.5 DALYs/1,000 population), 61% in men. Of the total, 51% corresponded to lung, colorectal, breast, stomach and prostate cancers. Mortality (84% of DALYs) predominated over disability. Subjects aged under 20 years accounted for 1.6% and those aged over 70 years accounted for 30.1% of DALYs.
Lung, colorectal and breast cancers are responsible for the highest number of DALYs in Spain. Even if the burden of disease due to cancer is predominantly caused by mortality, some cancers have a significant weight of disability. Information on 2000 burden of disease due to cancer can be useful to assess how it has evolved over time and the impact of medical advances on it in terms of mortality and disability.
PMCID: PMC2642814  PMID: 19183440
14.  Vascular comorbidity is associated with more rapid disability progression in multiple sclerosis 
Neurology  2010;74(13):1041-1047.
Vascular comorbidity adversely influences health outcomes in several chronic conditions. Vascular comorbidities are common in multiple sclerosis (MS), but their impact on disease severity is unknown. Vascular comorbidities may contribute to the poorly understood heterogeneity in MS disease severity. Treatment of vascular comorbidities may represent an avenue for treating MS.
A total of 8,983 patients with MS enrolled in the North American Research Committee on Multiple Sclerosis Registry participated in this cohort study. Time from symptom onset or diagnosis until ambulatory disability was compared for patients with or without vascular comorbidities to determine their impact on MS severity. Multivariable proportional hazards models were adjusted for sex, race, age at symptom onset, year of symptom onset, socioeconomic status, and region of residence.
Participants reporting one or more vascular comorbidities at diagnosis had an increased risk of ambulatory disability, and risk increased with the number of vascular conditions reported (hazard ratio [HR]/condition for early gait disability 1.51; 95% confidence interval [CI] 1.41–1.61). Vascular comorbidity at any time during the disease course also increased the risk of ambulatory disability (adjusted HR for unilateral walking assistance 1.54; 95% CI 1.44–1.65). The median time between diagnosis and need for ambulatory assistance was 18.8 years in patients without and 12.8 years in patients with vascular comorbidities.
Vascular comorbidity, whether present at symptom onset, diagnosis, or later in the disease course, is associated with a substantially increased risk of disability progression in multiple sclerosis. The impact of treating vascular comorbidities on disease progression deserves investigation.
= Expanded Disability Status Scale;
= hazard ratio;
= multiple sclerosis;
= North American Research Committee on Multiple Sclerosis;
= Patient Determined Disease Steps.
PMCID: PMC2848107  PMID: 20350978
15.  Valuation of health states in the U.S. study to establish disability weights: lessons from the literature 
The metric of disability-adjusted life years (DALYs) has become the global standard of measuring burden of disease. DALYs are comprised of years of life lost due to premature mortality and years of healthy life lost due to living with disability. In order to calculate the second part of the DALY equation, disease specific disability weights have to be established, i.e., measures for the decline of health associated with these disease states, which vary between 0 for perfect health and 1 for death. Although these disability weights are key for estimating DALYs, there have not been many comprehensive studies with empirical determinations of them. This article describes a systematic review on the state of the art with respect to empirically determining disability weights. Based on this review, a multi-method approach is outlined, which has also been implemented in a U.S. study to measure burden of disease. This approach involves the use of psychometric methodology as well as economic trade-off methods for determining the value of health states. It is conceptualized as a disaggregated approach, where the disability weight of any health state can be calculated if the attributes of this health state are known. The U.S. study received the collaboration of experts from more than 20 institutes of the National Institutes of Health and of the Centers for Disease Control and Prevention. First results will be available by the end of this year.
PMCID: PMC3306052  PMID: 20191661
disability-adjusted life years (DALYs); burden of disease; disability weight; empirical assessment; psychometrics; trade-off methods
16.  Burden of disease resulting from chronic mountain sickness among young Chinese male immigrants in Tibet 
BMC Public Health  2012;12:401.
In young Chinese men of the highland immigrant population, chronic mountain sickness (CMS) is a major public health problem. The aim of this study was to measure the disease burden of CMS in this population.
We used disability-adjusted life years (DALYs) to estimate the disease burden of CMS. Disability weights were derived using the person trade-off methodology. CMS diagnoses, symptom severity, and individual characteristics were obtained from surveys collected in Tibet in 2009 and 2010. The DALYs of individual patients and the DALYs/1,000 were calculated.
Disability weights were obtained for 21 CMS health stages. The results of the analyses of the two surveys were consistent with each other. At different altitudes, the CMS rates ranged from 2.1-37.4%; the individual DALYs of patients ranged from 0.13-0.33, and the DALYs/1,000 ranged from 3.60-52.78. The age, highland service years, blood pressure, heart rate, smoking rate, and proportion of the sample working in engineering or construction were significantly higher in the CMS group than in the non-CMS group (p < 0.05). These variables were also positively associated with the individual DALYs (p < 0.05). Among the symptoms, headaches caused the largest proportion of DALYs.
The results show that CMS imposes a considerable burden on Chinese immigrants to Tibet. Immigrants with characteristics such as a higher residential altitude, more advanced age, longer highland service years, being a smoker, and working in engineering or construction were more likely to develop CMS and to increase the disease burden. Higher blood pressure and heart rate as a result of CMS were also positively associated with the disease burden. The authorities should pay attention to the highland disease burden and support the development and application of DALYs studies of CMS and other highland diseases.
PMCID: PMC3444415  PMID: 22672510
chronic mountain sickness; burden of disease; disability-adjusted life years; disability weight; immigrant; high altitude
17.  Pulmonary impairment after tuberculosis and its contribution to TB burden 
BMC Public Health  2010;10:259.
The health impacts of pulmonary impairment after tuberculosis (TB) treatment have not been included in assessments of TB burden. Therefore, previous global and national TB burden estimates do not reflect the full consequences of surviving TB. We assessed the burden of TB including pulmonary impairment after tuberculosis in Tarrant County, Texas using Disability-adjusted Life Years (DALYs).
TB burden was calculated for all culture-confirmed TB patients treated at Tarrant County Public Health between January 2005 and December 2006 using identical methods and life tables as the Global Burden of Disease Study. Years of life-lost were calculated as the difference between life expectancy using standardized life tables and age-at-death from TB. Years lived-with-disability were calculated from age and gender-specific TB disease incidence using published disability weights. Non-fatal health impacts of TB were divided into years lived-with-disability-acute and years lived-with-disability-chronic. Years lived-with-disability-acute was defined as TB burden resulting from illness prior to completion of treatment including the burden from treatment-related side effects. Years lived-with-disability-chronic was defined as TB burden from disability resulting from pulmonary impairment after tuberculosis.
There were 224 TB cases in the time period, of these 177 were culture confirmed. These 177 subjects lost a total of 1189 DALYs. Of these 1189 DALYs 23% were from years of life-lost, 2% were from years lived-with-disability-acute and 75% were from years lived-with-disability-chronic.
Our findings demonstrate that the disease burden from TB is greater than previously estimated. Pulmonary impairment after tuberculosis was responsible for the majority of the burden. These data demonstrate that successful TB control efforts may reduce the health burden more than previously recognized.
PMCID: PMC2894771  PMID: 20482835
18.  The Pathogen- and Incidence-Based DALY Approach: An Appropriated Methodology for Estimating the Burden of Infectious Diseases 
PLoS ONE  2013;8(11):e79740.
In 2009, the European Centre for Disease Prevention and Control initiated the ‘Burden of Communicable Diseases in Europe (BCoDE)’ project to generate evidence-based and comparable burden-of-disease estimates of infectious diseases in Europe. The burden-of-disease metric used was the Disability-Adjusted Life Year (DALY), composed of years of life lost due to premature death (YLL) and due to disability (YLD). To better represent infectious diseases, a pathogen-based approach was used linking incident cases to sequelae through outcome trees. Health outcomes were included if an evidence-based causal relationship between infection and outcome was established. Life expectancy and disability weights were taken from the Global Burden of Disease Study and alternative studies. Disease progression parameters were based on literature. Country-specific incidence was based on surveillance data corrected for underestimation. Non-typhoidal Salmonella spp. and Campylobacter spp. were used for illustration. Using the incidence- and pathogen-based DALY approach the total burden for Salmonella spp. and Campylobacter spp. was estimated at 730 DALYs and at 1,780 DALYs per year in the Netherlands (average of 2005–2007). Sequelae accounted for 56% and 82% of the total burden of Salmonella spp. and Campylobacter spp., respectively. The incidence- and pathogen-based DALY methodology allows in the case of infectious diseases a more comprehensive calculation of the disease burden as subsequent sequelae are fully taken into account. Not considering subsequent sequelae would strongly underestimate the burden of infectious diseases. Estimates can be used to support prioritisation and comparison of infectious diseases and other health conditions, both within a country and between countries.
PMCID: PMC3835936  PMID: 24278167
19.  Subjective assessments of comorbidity correlate with quality of life health outcomes: Initial validation of a comorbidity assessment instrument 
Interventions to improve care for persons with chronic medical conditions often use quality of life (QOL) outcomes. These outcomes may be affected by coexisting (comorbid) chronic conditions as well as the index condition of interest. A subjective measure of comorbidity that incorporates an assessment of disease severity may be particularly useful for assessing comorbidity for these investigations.
A survey including a list of 25 common chronic conditions was administered to a population of HMO members age 65 or older. Disease burden (comorbidity) was defined as the number of self-identified comorbid conditions weighted by the degree (from 1 to 5) to which each interfered with their daily activities. We calculated sensitivities and specificities relative to chart review for each condition. We correlated self-reported disease burden, relative to two other well-known comorbidity measures (the Charlson Comorbidity Index and the RxRisk score) and chart review, with our primary and secondary QOL outcomes of interest: general health status, physical functioning, depression screen and self-efficacy.
156 respondents reported an average of 5.9 chronic conditions. Median sensitivity and specificity relative to chart review were 75% and 92% respectively. QOL outcomes correlated most strongly with disease burden, followed by number of conditions by chart review, the Charlson Comorbidity Index and the RxRisk score.
Self-report appears to provide a reasonable estimate of comorbidity. For certain QOL assessments, self-reported disease burden may provide a more accurate estimate of comorbidity than existing measures that use different methodologies, and that were originally validated against other outcomes. Investigators adjusting for comorbidity in studies using QOL outcomes may wish to consider using subjective comorbidity measures that incorporate disease severity.
PMCID: PMC1208932  PMID: 16137329
20.  Disability Weight of Clonorchis sinensis Infection: Captured from Community Study and Model Simulation 
Clonorchiasis is among the most neglected tropical diseases. It is caused by ingesting raw or undercooked fish or shrimp containing the larval of Clonorchis sinensis and mainly endemic in Southeast Asia including China, Korea and Vietnam. The global estimations for population at risk and infected are 601 million and 35 million, respectively. However, it is still not listed among the Global Burden of Disease (GBD) and no disability weight is available for it. Disability weight reflects the average degree of loss of life value due to certain chronic disease condition and ranges between 0 (complete health) and 1 (death). It is crucial parameter for calculating the morbidity part of any disease burden in terms of disability-adjusted life years (DALYs).
Methodology/Principal Findings
According to the probability and disability weight of single sequelae caused by C. sinensis infection, the overall disability weight could be captured through Monte Carlo simulation. The probability of single sequelae was gained from one community investigation, while the corresponding disability weight was searched from the literatures in evidence-based approach. The overall disability weights of the male and female were 0.101 and 0.050, respectively. The overall disability weights of the age group of 5–14, 15–29, 30–44, 45–59 and 60+ were 0.022, 0.052, 0.072, 0.094 and 0.118, respectively. There was some evidence showing that the disability weight and geometric mean of eggs per gram of feces (GMEPG) fitted a logarithmic equation.
The overall disability weights of C. sinensis infection are differential in different sex and age groups. The disability weight captured here may be referred for estimating the disease burden of C. sinensis infection.
Author Summary
Clonorchiasis is caused by eating incompletely cooked fishery product which carries the larval of Clonorchis sinensis. Millions of people are estimated to suffer in Southeast Asia. However, it is still among the most neglected tropical diseases due to the lack of clear evaluation, of which no disease burden available is one important reason. Our study is the first attempt to estimate the disability of C. sinensis infection, which reflects the average loss of life value due to some conditions and is crucial for calculating disease burden in terms of disability-adjusted life years (DALYs). After obtaining the probability and disability of single sequelae caused by C. sinensis infection through community investigation and literatures reviewing respectively, the overall disability was captured through model simulation. It was showed the overall disability of the male was higher than that of the female, positive correlation occurred between disability and infection intensity, and gallstone took the major attributable proportion. Thus, C. sinensis infection can cause apparent disability. The disability captured here may promote the further studies and benefit the final estimation of disease burden, which will promote health awareness and implementation of intervention.
PMCID: PMC3236727  PMID: 22180791
21.  A comparison of cancer burden and research spending reveals discrepancies in the distribution of research funding 
BMC Public Health  2012;12:526.
Ideally, the distribution of research funding for different types of cancer should be equitable with respect to the societal burden each type of cancer imposes. These burdens can be estimated in a variety of ways; “Years of Life Lost” (YLL) measures the severity of death in regard to the age it occurs, "Disability-Adjusted Life-Years" (DALY) estimates the effects of non-lethal disabilities incurred by disease and economic metrics focus on the losses to tax revenue, productivity or direct medical expenses. We compared research funding from the National Cancer Institute (NCI) to a variety of burden metrics for the most common types of cancer to identify mismatches between spending and societal burden.
Research funding levels were obtained from the NCI website and information for societal health and economic burdens were collected from government databases and published reports. We calculated the funding levels per unit burden for a wide range of different cancers and burden metrics and compared these values to identify discrepancies.
Our analysis reveals a considerable mismatch between funding levels and burden. Some cancers are funded at levels far higher than their relative burden suggests (breast cancer, prostate cancer, and leukemia) while other cancers appear underfunded (bladder, esophageal, liver, oral, pancreatic, stomach, and uterine cancers).
These discrepancies indicate that an improved method of health care research funding allocation should be investigated to better match funding levels to societal burden.
PMCID: PMC3411479  PMID: 22800364
Cancer; Research funding; Years of life lost; YLL; Disability adjusted life years; DALY; Burden; Economic cost
22.  Describing and Quantifying Asthma Comorbidty: A Population Study 
PLoS ONE  2012;7(5):e34967.
Asthma comorbidity has been correlated with poor asthma control, increased health services use, and decreased quality of life. Managing it improves these outcomes. Little is known about the amount of different types of comorbidity associated with asthma and how they vary by age.
Methodology/Principal Findings
The authors conducted a population study using health administrative data on all individuals living in Ontario, Canada (population 12 million). Types of asthma comorbidity were quantified by comparing physician health care claims between individuals with and without asthma in each of 14 major disease categories; results were adjusted for demographic factors and other comorbidity and stratified by age. Compared to those without asthma, individuals with asthma had higher rates of comorbidity in most major disease categories. Most notably, they had about fifty percent or more physician health care claims for respiratory disease (other than asthma) in all age groups; psychiatric disorders in individuals age four and under and age 18 to 44; perinatal disorders in individuals 17 years and under, and metabolic and immunity, and hematologic disorders in children four years and under.
Asthma appears to be associated with significant rates of various types of comorbidity that vary according to age. These results can be used to develop strategies to recognize and address asthma comorbidity to improve the overall health of individuals with asthma.
PMCID: PMC3346768  PMID: 22586445
23.  The cost of obesity in Canada 
BACKGROUND: Almost one-third of adult Canadians are at increased risk of disability, disease and premature death because of being obese. In order to allocate limited health care resources rationally, it is necessary to elucidate the economic burden of obesity. OBJECTIVE: To estimate the direct costs related to the treatment of and research into obesity in Canada in 1997. METHODS: The prevalence of obesity (body mass index of 27 or greater) in Canada was determined using data from the National Population Health Survey, 1994-1995. Ten comorbidities of obesity were identified from the medical literature. A population attributable fraction (PAF) was calculated for each comorbidity with data from large cohort studies to determine the extent to which each comorbidity and its management costs were attributable to obesity. The direct cost of each comorbidity was determined using data from the Canadian Institute of Health Information (for direct expenditure categories) and from Health Canada (for the proportion of expenditure category attributable to the comorbidity). This prevalence-based approach identified the direct costs of hospital care, physician services, services of other health professionals, drugs, other health care and health research. For each comorbidity, the cost attributable to obesity was determined by multiplying the PAF by the total direct cost of the comorbidity. The overall impact of obesity was estimated as the sum of the PAF-weighted costs of treating the comorbidities. A sensitivity analysis was completed on both the estimated costs and the PAFs. RESULTS: The total direct cost of obesity in Canada in 1997 was estimated to be over $1.8 billion. This corresponded to 2.4% of the total health care expenditures for all diseases in Canada in 1997. The sensitivity analysis revealed that the total cost could be as high as $3.5 billion or as low as $829.4 million; this corresponded to 4.6% and 1.1% respectively of the total health care expenditures in 1997. When the contributions of the comorbidities to the total cost were considered, the 3 largest contributors were hypertension ($656.6 million), type 2 diabetes mellitus ($423.2 million) and coronary artery disease ($346.0 million). INTERPRETATION: A considerable proportion of health care dollars is devoted to the treatment and management of obesity-related comorbidities in Canada. Further research into the therapeutic benefits and cost-effectiveness of management strategies for obesity is required. It is anticipated that the prevention and treatment of obesity will have major positive effects on the overall cost of health care.
PMCID: PMC1230073  PMID: 10081464
24.  Using Disability-Adjusted Life Years to Assess the Burden of Disease and Injury in Rhode Island 
Public Health Reports  2012;127(3):293-303.
Disability-adjusted life years (DALYs) measure the burden of disease and injury in a population. We tested the feasibility of calculating DALYs to assess the burden of disease and injury in Rhode Island (RI).
We computed DALYs for the 2008 RI population using methods developed by the World Health Organization, Harvard University, and the World Bank. DALYs are a composite measure that sum years of life lost (YLLs) due to premature mortality with years lived with disability (YLDs). We calculated crude mortality, YLLs, YLDs, and DALYs for 90 major health conditions for RI and stratified them by gender and age. Calculations for YLLs and YLDs were based on five-year averages. We compared our results with U.S. and Los Angeles County, California, estimates.
A DALYs ranking produces a different picture of RI's disease and injury burden than does mortality-based ranking. Of 90 major health conditions assessed for RI, six of the top 10 causes for mortality and DALYs were the same, but were ranked differently: ischemic heart disease, cerebrovascular disease, Alzheimer dementia and other dementias, trachea/bronchus/lung cancer, chronic obstructive pulmonary disease, and diabetes mellitus. These six conditions accounted for 59% of deaths but only 35% of DALYs. Causes and rank orders for DALYs differed between males and females and among age groups.
Including nonfatal health conditions in an assessment of population health provides a different picture than traditional mortality-based assessments. This study demonstrates the feasibility and constraints of using DALYs to assess the burden of disease and injury at the state level.
PMCID: PMC3314073  PMID: 22547860
25.  Development of Methodology for Disability-Adjusted Life Years (DALYs) Calculation Based on Real-Life Data 
PLoS ONE  2013;8(9):e74294.
Disability-Adjusted Life Years (DALYs) have the advantage that effects on total health instead of on a specific disease incidence or mortality can be estimated. Our aim was to address several methodological points related to the computation of DALYs at an individual level in a follow-up study.
DALYs were computed for 33,507 men and women aged 20–70 years when participating in the EPIC-NL study in 1993–7. DALYs are the sum of the Years Lost due to Disability (YLD) and the Years of Life Lost (YLL) due to premature mortality. Premature mortality was defined as death before the estimated date of individual Life Expectancy (LE). Different methods to compute LE were compared as well as the effect of different follow-up periods using a two-part model estimating the effect of smoking status on health as an example.
During a mean follow-up of 12.4 years, there were 69,245 DALYs due to years lived with a disease or premature death. Current-smokers had lost 1.28 healthy years of their life (1.28 DALYs 95%CI 1.10; 1.46) compared to never-smokers. The outcome varied depending on the method used for estimating LE, completeness of disease and mortality ascertainment and notably the percentage of extinction (duration of follow-up) of the cohort.
We conclude that the use of DALYs in a cohort study is an appropriate way to assess total disease burden in relation to a determinant. The outcome is sensitive to the LE calculation method and the follow-up duration of the cohort.
PMCID: PMC3779209  PMID: 24073206

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