BC Jung A Brief Introduction to Epidemiology - XI (Epidemiologic Research Designs: Experimental/Interventional Studies) Betty C. Jung, RN, MPH, CHES

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

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.

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)

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)

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

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).

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

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

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.

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!

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

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

BC Jung Randomized Trial Design Time Defined Population New Treatment Current Treatment Improved Not Improved Improved Not Improved RANDOMIZEDRANDOMIZED

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

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

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

BC Jung References u For Internet Resources on the topics covered in this lecture, check out my Web site: