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 FUTUREPRESENT RetrospectiveProspectiveCross-sectional Time

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 Denmark Pittsburgh, USA Scotland Sweden Finland Korea Japan Kuwait Israel England Canada Netheland Incidence /100,000

RETROSPECTIVE STUDY Time PAST Life style Diet Reproductive on Medication Family Hx Genetics PRESENT Disease Determining differences in:

RETROSPECTIVE STUDY: PROS & CONS Suitable for rare diseases Inexpensive Minimal ethical problems Short study time Small # of subjects Subjects need not volunteer 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 PROCON

PROSPECTIVE STUDY PRESENT DM Time Future Risk factors??? Retinopathy- Retinopathy+

PROSPECTIVE STUDY: PROS & CONS Less variability to bias No recall necessary Incidence determined Relative risk accurate 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 PROCON

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 Random Selection Exercise Diet Drug Outcome evaluation

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?