The uses of 'Uses of epidemiology'

The epidemiology of Parkinson's disease

The epidemiology of Parkinson's disease shows marked variations in time, geography, ethnicity, age, and sex. Internationally, prevalence has increased over and above demographic changes. There are several potential reasons for this increase, including the decline in other competing causes of death. Whether incidence is increasing, especially in women or in many low-income and middle-income countries where there is a shortage of high-quality data, is less certain. Parkinson's disease is more common in older people and men, and a variety of environmental factors have been suggested to explain why, including exposure to neurotoxic agents. Within countries, there appear to be ethnic differences in disease risk, although these differences might reflect differential access to health care. The cause of Parkinson's disease is multifactorial, and involves genetic and environmental factors. Both risk factors (eg, pesticides) and protective factors (eg, physical activity and tendency to smoke) have been postulated to have a role in Parkinson's disease, although elucidating causality is complicated by the long prodromal period. Following the establishment of public health strategies to prevent cardiovascular diseases and some cancers, chronic neurodegenerative diseases such as Parkinson's disease and dementia are gaining a deserved higher priority. Multipronged prevention strategies are required that tackle population-based primary prevention, high-risk targeted secondary prevention, and Parkinson's disease-modifying therapies for tertiary prevention. Future international collaborations will be required to triangulate evidence from basic, applied, and epidemiological research, thereby enhancing the understanding and prevention of Parkinson's disease at a global level.

Lipid levels linked to symptomatic aortic valve stenosis: evidence from Mendelian randomization?

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Post-Modern Epidemiology: When Methods Meet Matter

In the last third of the 20th century, etiological epidemiology within academia in high-income countries shifted its primary concern from attempting to tackle the apparent epidemic of noncommunicable diseases to an increasing focus on developing statistical and causal inference methodologies. This move was mutually constitutive with the failure of applied epidemiology to make major progress, with many of the advances in understanding the causes of noncommunicable diseases coming from outside the discipline, while ironically revealing the infectious origins of several major conditions. Conversely, there were many examples of epidemiologic studies promoting ineffective interventions and little evident attempt to account for such failure. Major advances in concrete understanding of disease etiology have been driven by a willingness to learn about and incorporate into epidemiology developments in biology and cognate data science disciplines. If fundamental epidemiologic principles regarding the rooting of disease risk within populations are retained, recent methodological developments combined with increased biological understanding and data sciences capability should herald a fruitful post-Modern Epidemiology world.

'A matter of commonsense': the Coventry poliomyelitis epidemic 1957 and the British public

In 1956, the British Ministry of Health instituted a vaccination programme against poliomyelitis, but run into myriad supply and administrative issues. When Coventry experienced an epidemic in 1957, it came to symbolise these problems. Throughout, it was claimed that the government lacked 'common sense'. This article explores how and why 'common sense' was used as a rhetorical weapon in the debates over policy at the local and national level. While those claiming 'common sense' were often at odds with medical and administrative authorities, the arguments were often informed by deeply held beliefs about vaccination and disease.

The potential application of personalized preventive research

With increases in life expectancy, the focus has shifted to living a healthier, longer life. By concentrating on preventing diseases before occurrence, researchers aim to diminish the increasing gap in medical costs and health inequalities prevalent across many nations. Although we have entered an era of post-genomics, we are still in infancy in terms of personalized preventive research. Personalized preventive research has and will continue to improve with advancements in the use of biomarkers and risk assessment. More evidence based on well-designed epidemiologic studies is required to provide comprehensive preventive medical care based on genetic and non-genetic profile data. The realization of personalized preventive research requires building of evidence through appropriate methodology, verification of results through translational studies as well as development and application of prediction models.

Who and what is a "population"? Historical debates, current controversies, and implications for understanding "population health" and rectifying health inequities

CONTEXT

The idea of "population" is core to the population sciences but is rarely defined except in statistical terms. Yet who and what defines and makes a population has everything to do with whether population means are meaningful or meaningless, with profound implications for work on population health and health inequities.

METHODS

In this article, I review the current conventional definitions of, and historical debates over, the meaning(s) of "population," trace back the contemporary emphasis on populations as statistical rather than substantive entities to Adolphe Quetelet's powerful astronomical metaphor, conceived in the 1830s, of l'homme moyen (the average man), and argue for an alternative definition of populations as relational beings. As informed by the ecosocial theory of disease distribution, I then analyze several case examples to explore the utility of critical population-informed thinking for research, knowledge, and policy involving population health and health inequities.

FINDINGS

Four propositions emerge: (1) the meaningfulness of means depends on how meaningfully the populations are defined in relation to the inherent intrinsic and extrinsic dynamic generative relationships by which they are constituted; (2) structured chance drives population distributions of health and entails conceptualizing health and disease, including biomarkers, as embodied phenotype and health inequities as historically contingent; (3) persons included in population health research are study participants, and the casual equation of this term with "study population" should be avoided; and (4) the conventional cleavage of "internal validity" and "generalizability" is misleading, since a meaningful choice of study participants must be in relation to the range of exposures experienced (or not) in the real-world societies, that is, meaningful populations, of which they are a part.

CONCLUSIONS

To improve conceptual clarity, causal inference, and action to promote health equity, population sciences need to expand and deepen their theorizing about who and what makes populations and their means.

The burden of headache disorders in India: methodology and questionnaire validation for a community-based survey in Karnataka State

Primary headache disorders are a major public-health problem globally and, possibly more so, in low- and middle-income countries. No methodologically sound studies of prevalence and burden of headache in the adult Indian population have been published previously. The present study was a door-to-door cold-calling survey in urban and rural areas in and around Bangalore, Karnataka State. From 2,714 households contacted, 2,514 biologically unrelated individuals were eligible for the survey and 2,329 (92.9 %) participated (1,103 [48 %] rural; 1,226 [52 %] urban; 1,141 [49 %] male; 1,188 [51 %] female; mean age 38.0 years). The focus was on primary headache (migraine and tension-type headache [TTH]) and medication-overuse headache. A structured questionnaire administered by trained lay interviewers was the instrument both for diagnosis (algorithmically determined from responses) and burden estimation. The screening question enquired into headache in the last year. The validation study compared questionnaire-based diagnoses with those obtained soon after through personal interview by a neurologist in a random sub-sample of participants (n = 381; 16 %). It showed high values (> 80 %) for sensitivity, specificity and predictive values for any headache, and for specificity and negative predictive value for migraine and TTH. Kappa values for diagnostic agreement were good for any headache (0.69 [95 % CI 0.61-0.76]), moderate (0.46 [0.35-0.56]) for migraine and fair (0.39 [0.29-0.49]) for TTH. The survey methodology, including identification of and access to participants, proved feasible. The questionnaire proved effective in the survey population. The study will give reliable estimates of the prevalence and burden of headache, and of migraine and TTH specifically, in urban and rural Karnataka.

Migration, neighborhoods, and networks: approaches to understanding how urban environmental conditions affect syndemic adverse health outcomes among gay, bisexual and other men who have sex with men

Adopting socioecological, intersectionality, and lifecourse theoretical frameworks may enhance our understanding of the production of syndemic adverse health outcomes among gay, bisexual and other men who have sex with men (MSM). From this perspective, we present preliminary data from three related studies that suggest ways in which social contexts may influence the health of MSM. The first study, using cross-sectional data, looked at migration of MSM to the gay resort area of South Florida, and found that amount of time lived in the area was associated with risk behaviors and HIV infection. The second study, using qualitative interviews, observed complex interactions between neighborhood-level social environments and individual-level racial and sexual identity among MSM in New York City. The third study, using egocentric network analysis with a sample of African American MSM in Baltimore, found that sexual partners were more likely to be found through face-to-face means than the Internet. They also observed that those who co-resided with a sex partner had larger networks of people to depend on for social and financial support, but had the same size sexual networks as those who did not live with a partner. Overall, these findings suggest the need for further investigation into the role of macro-level social forces on the emotional, behavioral, and physical health of urban MSM.

Social class, family history and type of schizophrenia

To date, there are numerous studies supporting a genetic model of schizophrenia. There is a paucity of studies, however, screening for a connection between family history of serious mental illness and deficit vs. nondeficit schizophrenia. The aim of the present study was to explore the association between family history, deficit vs. nondeficit schizophrenia and socioeconomic status (SES) of family of origin. Patients (N=437) from a United States psychiatric hospital were separated into deficit vs. nondeficit presentation and bifurcated into poor vs. nonpoor SES. Family history data were utilized to classify patients into subgroups characterized by serious mental illness within immediate family, within extended family, or no evidence of mental illness. Statistical testing was conducted using logistic regression analysis. SES of family of origin was significantly associated with schizophrenic subtype independently of family history, sex and race; specifically, poverty raised the risk of deficit schizophrenia. Family history of mental illness showed no net association, and no statistical interaction with poverty, in predicting risk of deficit schizophrenia.

Schizophrenic subtype, seasonality of birth and social class: a preliminary analysis

OBJECTIVE

The neurodevelopmental model of schizophrenia includes the etiological impact of fetal brain stressors possibly connected with birth seasonality. Specification of social class of origin (SES) as a related risk factor remains unexamined as does type of schizophrenia as an outcome variable. The objective of this study was to test for an interconnection between SES, type of schizophrenia and seasonality of birth.

METHODS

Patients (N=436) from a United States psychiatric hospital were separated into deficit/non-deficit presentation and bifurcated into poor/non-poor SES. Birth seasonality was assessed by months hypothetically connected with winter-related trimesters of gestation.

RESULTS

Results showed that there is a significant difference (p=0.0411) in the monthly birth patterns of poor vs. non-poor patients and that the difference connects with the likelihood of deficit vs. non-deficit schizophrenia. Specifically, an elevated proportion of patients with deficit schizophrenia were born to impoverished women who likely conceived in January. Findings were confirmed by multiple levels of statistical assessment including log linear analysis.

CONCLUSION

The resultant model suggests the environmental location (lower SES) and timing (winter conception) of adult schizophrenia with poor outcome (deficit).

Invited commentary: taking the search for causes of schizophrenia to a different level

In recent years, epidemiologists have established major variations in the incidence of schizophrenia and have begun to investigate the causes of these variations. The report by Pedersen and Mortensen (Am J Epidemiol 2006;163:971-8) in this issue of the Journal examines the contribution of family-level factors to the urban-rural difference in the incidence of schizophrenia. Their results suggest that familial life in urban environments confers some effect that persists after families move to rural settings. Taking these findings together with those of previous studies, it appears that factors operating at the level of the social context, the family, and the individual may all contribute to the urban-rural difference in schizophrenia incidence. This work exemplifies an integrative, multilevel approach to epidemiologic research that employs principles central to eco-epidemiology and other, similar frameworks.

Sedentary lifestyles, physical activity, and cardiovascular disease: from research to practice

More than 60% of the world's population is not physically active at levels that promote health. In concert with other behavioral risk factors for cardiovascular disease (CVD), sedentary lifestyles exact a heavy medical and economic toll on individuals and societies. Physical activity lowers all-cause mortality, reduces several risk factors for cardiovascular disease, and is a category 2 intervention that can halve cardiovascular disease risk. The benefits extend across a wide spectrum of structured as well as lifestyle physical activity levels. Models and programs aimed at translating physical activity's promise in cardiovascular prevention have been assessed, but results have been generally disappointing. A pragmatic strategy based on the "stages of change" or transtheoretical model can be effective. It incorporates self efficacy and individual initiatives, both crucial ingredients necessary to surmount the inevitable hurdles on the path towards physically active lifestyles.

Is income inequality a determinant of population health? Part 2. U.S. National and regional trends in income inequality and age- and cause-specific mortality

This article describes U.S. income inequality and 100-year national and 30-year regional trends in age- and cause-specific mortality. There is little congruence between national trends in income inequality and age- or cause-specific mortality except perhaps for suicide and homicide. The variable trends in some causes of mortality may be associated regionally with income inequality. However, between 1978 and 2000 those regions experiencing the largest increases in income inequality had the largest declines in mortality (r= 0.81, p < 0.001). Understanding the social determinants of population health requires appreciating how broad indicators of social and economic conditions are related, at different times and places, to the levels and social distribution of major risk factors for particular health outcomes.

'Mendelian randomization': can genetic epidemiology contribute to understanding environmental determinants of disease?

Associations between modifiable exposures and disease seen in observational epidemiology are sometimes confounded and thus misleading, despite our best efforts to improve the design and analysis of studies. Mendelian randomization-the random assortment of genes from parents to offspring that occurs during gamete formation and conception-provides one method for assessing the causal nature of some environmental exposures. The association between a disease and a polymorphism that mimics the biological link between a proposed exposure and disease is not generally susceptible to the reverse causation or confounding that may distort interpretations of conventional observational studies. Several examples where the phenotypic effects of polymorphisms are well documented provide encouraging evidence of the explanatory power of Mendelian randomization and are described. The limitations of the approach include confounding by polymorphisms in linkage disequilibrium with the polymorphism under study, that polymorphisms may have several phenotypic effects associated with disease, the lack of suitable polymorphisms for studying modifiable exposures of interest, and canalization-the buffering of the effects of genetic variation during development. Nevertheless, Mendelian randomization provides new opportunities to test causality and demonstrates how investment in the human genome project may contribute to understanding and preventing the adverse effects on human health of modifiable exposures.