TYPES OF EPIDEMIOLOGICAL STUDIES 1 Descriptive studies Describing

TYPES OF EPIDEMIOLOGICAL STUDIES: 1. Descriptive studies: Describing disease by person, time and place. 2. Analytical studies : looking for associations and testing hypotheses 3. Experimental studies: testing the effect of interventions or services on disease

DESCRIPTIVE STUDIES • Descriptive epidemiological studies provide Information on characteristics which will provide clue to epidemiological hypothesis. These studies concerned with; disease distribution according to person (population subgroups), Place (certain area), and time (certain time)

BENEFITS OF DESCRIPTIVE STUDIES:

Types 1. Cross-sectional studies 2. Correlational studies 3. Case report and case series

CROSS-SECTIONAL STUDIES (Characteristics)

2 -CORRELATIONAL STUDIES

2 -CORRELATIONAL STUDIES LIMITATION;

3 -CASE REPORT AND CASE SERIES (Characteristics)

Methods of hypothesis formulation;

2 -Analytic studies As you have seen, with descriptive studies we can identify several characteristics of persons with disease, and we may question whether these features are really unusual, but descriptive epidemiology does not answer that question.

2 -Analytic studies Analytic epidemiology provides a way to find the answer. The comparison group or groups, which provide baseline data, are a key feature of analytic epidemiology. The investigator simply observes the natural course of events (noting if the persons exposed or not, and if they developed outcome or not).

Analytical (Observational) studies is of two basic types; Case control studies and cohort studies.

1 -Case-control study Characteristics

Selection of cases; • Sources include;

Selection of controls; • Sources of controls;

Size of the sample of the control:

Bias in case-control studies: • Bias is any systematic error in the determination of the association between the exposure and the disease. Role of bias;

2 -Cohort studies;

Advantages of cohort studies;

Disadvantages;

Types of cohort • Cohort is divided into types depending on the temporal relationship between the initiation of the study and the occurrence of the disease. • 1 - Retrospective cohort;

2 - Prospective cohort;

Retrospective & Prospective: • Retrospective: looks backward from a disease to a possible cause. • Prospective; looks forward from an exposure to an outcome. • The feature that distinguishes a prospective from a retrospective cohort is simply and solely whether the outcome of interest has occurred at time of study initiation