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

Retrospective ProspectiveCross-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

0 10 20 30

Denmark

Pittsburgh, USAScotlandSweden

Finland

KoreaJapan

KuwaitIsrael

EnglandCanada

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

PRO CON

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

PRO CON

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 STUDYRandomized Clinical Trial:DPP

Random Selection

Exercise

Diet

Drug

Ou

tcome evalu

ation

EXPERIMENTAL STUDYCross-over design

Ou

tcome evalu

ation

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?