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TYPES OF STUDIES IN DIABETES EPIDEMIOLOGY Nam-Ham Cho, Ajou University TYPES OF STUDIES BASED ON: • Purpose • Time • Cost • Feasibility TYPES OF STUDY Observational Descriptive Analytical – Cross-sectional – Retrospective – Prospective Experimental – Clinical Trial – Community Intervention Trial – Field Trial A STUDY DESIGN FOR THE OUTCOMES OF DIABETES • Diabetes • Morbidity (Complications) • Mortality (Death) • Economics • Treatment • Education • Prevention & Control • Intervention TIME AND TYPES OF STUDY PAST PRESENT Retrospective Cross-sectional Time FUTURE Prospective CROSS-SECTIONAL STUDY PRESENT Cross-sectional Time ANALYTICAL STUDY A cross-sectional study: – Privides a snap shot – Is simple – Provides associated factor – Is first line of epidemiologic research CROSS-SECTIONAL STUDY What is different about: • DM • Morbidity (Complications) • Mortality (Death) How is it different about: • SES • Age at onset • Season CROSS-SECTIONAL STUDY Korea Japan Kuwait Israel England Canada Netheland Denmark Pittsburgh, USA Scotland Sweden Finland 0 10 20 Incidence /100,000 30 RETROSPECTIVE STUDY Determining differences in: • • • • • • Life style Diet Reproductive on Medication Family Hx Genetics PRESENT PAST Time Disease RETROSPECTIVE STUDY: PROS & CONS PRO • • • • • • Suitable for rare diseases Inexpensive Minimal ethical problems Short study time Small # of subjects Subjects need not volunteer CON • • • • • Susceptable to selection & memory bias Inconsistency: definitions of symptoms or diseases may have been modified over time. Can not determine incidence Limitations in data Relative risk approximation PROSPECTIVE STUDY Retinopathy+ PRESENT DM Risk factors??? Future Retinopathy- Time PROSPECTIVE STUDY: PROS & CONS PRO • • • • Less variability to bias No recall necessary Incidence determined Relative risk accurate CON • • • • • • • • • Consistent disease definitions & symptoms. Longer time Common disease only Expensive Ethical concern A high drop-out rate Volunteers needed A large # of subjects needed The Hawthorne-effect TYPES OF STUDIES AND GOALS CROSS-SECTIONAL Understand RETROSPECTIVE Estimate risk factors PROSPECTVE Validate risk factors Prevention-Control-Intervention-Education-Management EXPERIMENTAL STUDY • Animal • Drug trials • Human EXPERIMENTAL STUDY Randomized Clinical Trial:DPP Exercise Diet Drug Outcome evaluation Random Selection EXPERIMENTAL STUDY Cross-over design Outcome evaluation Review Questions (Developed by the Supercourse team) • What are the advantages and disadvantages for retrospective studies? •What are the advantages and disadvantages for prospective studies?
