Case-control studies exposure measurements

Any study of lung cancer-radon exposure correlations, including both case-control studies and the one considered here, must infer radon exposures many decades ago from measurements made at present. 

Cohort and case-control studies relate the exposures under study to the occurrence of cancer in individuals and provide an estimate of relative risk (ratio of incidence or mortality in those exposed to incidence or mortality in those not exposed) as the main measure of association. 

The biomarker is validated in a cross-sectional population-based study to determine if there are correlations between self-reported HCA exposure (for example, food frequency questionnaire using photographs similar to the case-control study reported by Butler et al.) and HCA measurements. 

Examples of Biomarkers of Exposure. In the studies described in Section 26.1, biomarkers were not used to measure meat consumption or HCA intake. In the case-control study reported by Butler et al. (Example 1.3), HCA intake was assessed... 

EXPOSURES RELEVANT TO HEALTH THE CONCEPTUAL FRAMEWORK 246 Considerations of Exposure Timing 246 Considerations of Exposure Route 247 Practical Context of Pesticide Exposure 248 EPIDEMIOLOGICAL STUDY DESIGNS AND EXPOSURE ASSESSMENT 248 Prospective Cohort Studies 248 Retrospective Cohort Studies 249 Case-Control Studies 250 Cross-Sectional Studies 252 EXPOSURE ASSESSMENT STRATEGIES 252 INFLUENCE OF THE ACCURACY OF EXPOSURE PROXIES ON MEASURES OF ASSOCIATION 254 Errors in Qualitative Proxies 254... 

First, this chapter will describe a conceptual framework to illustrate the special challenges posed because exposures assessed for epidemiologic studies must be relevant to the health outcome under investigation. Secondly, some of the most commonly applied epidemiological study designs will be introduced, with special emphasis on exposnre assessment issnes associated with the design. Thirdly, some widely applied exposure assessment approaches will be introduced, ranging from qualitative classifications of exposure to quantitative exposure assessment of pesticide concentrations. The influence of measurement error on measures of association between exposure and disease, such as the slopes of exposure-response relationships and risk or odds ratios, will be briefly reviewed. Finally, exposure proxies used in case-control studies of chronic effects of pesticide exposure will be reviewed and the concepts introduced earlier will be applied. 

An avenue for both occupational and enviromnental exposure assessment which has only rarely been used in case-control studies is direct exposure measurements of the study subjects. For pesticides with long biological half-lives, and whose concentrations are unlikely to be affected by the disease, biological measures of exposure can be made. For example, Caldwell etal. (1981) and Scheele etal. (1992, 1996) measured pesticide levels in bone marrow and serum in adult and childhood cancer cases and controls. 

The two basic types of analytical studies are the cohort and the case-control study. Each has strengths and weaknesses as well as different resource and time requirements. The cohort study involves the study of indi iduals classified by exposure characteristics, e.g., a group of welders. The study then follows the development of disease in the welders group as well as in an unexposed comparison population. The measure that assesses the magnitude of... 

In correlation studies, the unit of investigation is usually whole populations (eg, particular geographical areas) and cancer frequency is related to a summary measure of the exposure of the population to the agent. Because individual exposure is not documented, a causal relationship is less easy to infer from such studies than from cohort and case-control studies. Case reports generally arise from a suspicion, based on clinical experience, that the concurrence of 2 events — that is, a particular exposure and occurrence of a cancer — has happened rather more frequently than would be expected by chance. The uncertainties surrounding interpretation of case reports and correlation studies make them inadequate, except in rare cases, to form the sole basis for inferring a causal relationship. 

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