朝阳区病残儿医学鉴定与审批工作流.ppt

A Brief Introduction to Epidemiology - IX (Epidemiologic Research Designs: Case-Control Studies),Betty C. Jung, RN, MPH, CHES,Learning/Performance Objectives,To develop an understanding of: What case-control studies are The value of such studies The basic methodology Pros and Cons of such studies,Introduction,Epidemiology studies the distribution of disease in a number of ways. The two major categories of epidemiological studies are: Observational and experimental studies. Most epidemiological studies are observational.,Epidemiological Study Designs,Observational Studies - examine associations between risk factors and outcomes (Analytical - determinants and risk of disease, and descriptive - patterns and frequency of disease) Intervention Studies - explore the association between interventions and outcomes. (Experimental studies or clinical trials),Research Designs in Analytic Epidemiology,Ecologic Designs Cross-Sectional Study Case-Control Study Cohort Study,Case-Control Studies,“Flashback Studies” (Paffenbarger, 1988) Retrospective - compare cases and controls for presence of disease Includes passage of time. Historical - assess past characteristics or exposures in two groups of people- cases and controls,Examples,The relationship between thalidomide and unusual limb defects in Germany The relationship between meat consumption and enteritis necroticans in Papua New Guinea,Value,Simple to conduct Cost-effective way to study a rare disease,Case-Control Studies: Methodology,Then measure, post-exposure,First Select the Cases and Controls,Cases,(with,disease),Control (without disease),Were Exposed,A,B,Not Exposed,C,D,A+C,B+D,Population Exposed,A/A+C,B./B+D,Case Control Design,Time Direction of Inquiry,Population,Cases with the Disease,Controls without the disease,Exposed,Exposed,Not Exposed,Not Exposed,Case-Control Studies,Cases - Has condition or health outcome of interest. Has higher frequency or greater degree of exposure than non-cases. Controls (non-cases) - Does not have the health condition. Serves as the comparison group Ask about history of contact with or exposure to supposed causes,Case-Control Studies,If controls are well chosen, the only antecedent difference will be in the level of a characteristic that is related causally to the development of a disease (I.e, exposure to a chemical resulted in cancer). Quantify with odds ratios,Strength of Association,Relative Risk;(Prevalence); Odds Ratio Strength of Association 0.83-1.00 1.0-1.2 None 0.67-0.83 1.2-1.5 Weak 0.33-0.67 1.5-3.0 Moderate 0.10-0.33 3.0-10.00 Strong 10.0 Approaching Infinity,Methodology Issue: Matching,Matching - control for confounding variables. If you do not match then control by subject selection (study only males to eliminate gender as a confounding variable) Matching Subject selection Statistical control during data analysis The more variables that need to be matched the greater the universe we need. Problem - match age, sex and SES - Control must be the same.,Methodological Weaknesses,Biased reporting of the antecedent (having lung CA - patients over reporting smoking (from guilt, knowledge or selective memory) Subject selection (decreases with cases and controls in the same facility) Limited to only cases, who have survived at the same time. Selective survival,Pros,Cases easily available Good for less common or rare cases Quick, inexpensive Can be conducted by clinicians in clinical facilities Tend to support, not prove causal hypothesis by establishing associations Historical data available in clinical records Number of subjects needed is small,Cons,Info about antecedents depends on memory, which could lead to bias Clinical data may be inadequate or incomplete “Case group” may not be homogenous - criteria for diagnosis may differ. Clinical cases are selective survivors,Cons,Non-representativeness of cases. Those coming in for treatment may differ from those not seeking treatment and those going somewhere else. Antecedent is not obtained from universe of all antecedents. Berksons fallacy - making generalizations from hospital or clinical samples to the general population. Cannot know what a