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BC Jung A Brief Introduction to Epidemiology - XI (Epidemiologic Research Designs: Experimental/Interventional Studies) Betty C. Jung, RN, MPH, CHES
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BC Jung Learning Objectives u To understand: – What experimental studies are – The value of such studies –The basic methodology –Pros and Cons of such studies
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BC Jung Introduction The primary purpose of research is to conduct a scientific, or, scholarly investigation into a phenomenon, or to answer a burning question. Research is defined as a systematic approach to problem solving.
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BC Jung Epidemiological Study Designs u Observational Studies - examine associations between risk factors and outcomes (Analytical - determinants and risk of disease, and descriptive - patterns and frequency of disease) u Intervention Studies - explore the association between interventions and outcomes. (Experimental studies or clinical trials)
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BC Jung Epidemiological Study Designs u Observational –Cross-Sectional –Case-control –Cohort u Interventional –Natural Experiment (Community Trial) –Field Trial –Experiment/Randomized Trails (ex. Clinical Trial)
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BC Jung Examples of Experimental Epidemiologic Studies u Prophylactic vaccines tested on children populations to prove the efficacy of the vaccines in preventing the diseases (i.e., polio) u Prophylaxis with drugs in preventing disease (i.e., penicillin to prevent rheumatic fever) u Impact on health-related behavior and coronary heart disease in response to community-wide heart disease prevention intervention
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BC Jung Value u Experiments are seen as the “Supreme Court” of epidemiologic research as they provide the strongest possible evidence of disease causation. u Experimental study designs can rule out with greater certainty factors that may confound potential cause and affect relationships. u A study’s degree of internal validity depends on the study design’s ability to determine whether an antecedent causes an effect (or outcome).
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BC Jung Community Trials u Communities rather than individuals comprise the treatment groups u Appropriate for diseases that have their origins in social conditions that can be influenced by intervention directed at group behavior as well as individuals
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BC Jung Limitations of Community Trials u Random allocation of communities is not practical u Only a small number of communities can be included u Other methods are needed to ensure any difference found can be attributed to the intervention rather than to any inherent differences between the communities studied
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BC Jung Field Trials u Involve people who are disease-free but presumed to be at risk u Data collection – “in the field” – among non-institutionalized people in the general population u Used to evaluate interventions that reduce exposure without measuring the occurrence of health effects.
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BC Jung Limitations of Field Trials u Hugh undertaking u Major logistic considerations u Major financial considerations u Think of how much work is required to randomize and allocate participants to various treatment groups!
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BC Jung Experimental Study Design Time Sample of Cases Treated (T) Not Treated (NT) (Control) Treated - Improved Treated – Not Improved Not Treated - Improved Not Treated – Not Improved
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BC Jung Randomized Trial Methodology u Random allocation - Each subject has an equal chance of being assigned to any group in the study, so that all groups in a study are similar in all characteristics not controlled by other methods, such as subject selection. u Random allocation can be used with matching to ensure the study groups are comparable
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BC Jung Randomized Trial Design Time Defined Population New Treatment Current Treatment Improved Not Improved Improved Not Improved RANDOMIZEDRANDOMIZED
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BC Jung Four Possibilities u The treatments do not differ and we correctly conclude they do not differ u The treatments do not differ but we conclude they do differ u The treatments differ but we conclude they do not differ u The treatments do differ and we correctly conclude that they do differ
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BC Jung Pros u Helpful in assessing the value of new therapies to combat acute diseases in developing countries u Can evaluate a single variable in a precisely defined patient group u Prospective design u Eliminates bias by comparing two otherwise identical groups u Allows for meta-analysis
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BC Jung Cons u Expensive and time consuming u Not always properly conducted – too few subjects, too short a time period u Influence of sponsorship u Use of surrogate endpoints may introduce “hidden bias” u Failure to randomize all eligible subjects u Failure to blind assessors to randomized status of subjects
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BC Jung References u For Internet Resources on the topics covered in this lecture, check out my Web site: http://www.bettycjung.net/
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