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• A study design is a specific plan or protocol for conducting the study, which allows the investigator to translate the conceptual hypothesis into an operational one.
ConceptEpidemiological studies are essential to• identify health needs• formulate hypothesis• examine pattern of disease problems within and between
populations• look for causes• formulate health promotion, prevention and control
strategies• study of natural history of disease• plan for health services• evaluate health services• classify disease, develop priorities• study distribution of normal biological characteristics• evaluate risk factors
Type of study designs1. Observational studies
In observational studies, the investigator allows the nature to take its course. He/she observes and measures the characteristics of interest to the study, and does not intervene or control the factors related to exposure or outcome.
a. Descriptive studies: It describes the occurrence and distribution of disease in the study population. It is often the first step in epidemiological studies e.g. case reports and case studies
b. Analytical studies: It analyzes the relationship between dependent and independent variables (exposure and outcome) under the existing natural conditions e.g. case control and cohort studies
2. Experimental studies
Experimental studies are designed to evaluate the effectiveness of certain interventions.
On the basis of time period of the study, epidemiological studies are of two types:
1. Cross-sectional study: The study is done at one point in time.
2. Longitudinal study: Longitudinal study is done over a prolonged period of time by means of follow up examinations.
• Non intervention studies: The researcher just describes and analyzes researchable objects or situations but does not intervene.
• Intervention studies: The researcher just describes and manipulates objects or situations, either by preventive or therapeutic measures, and determines the outcome of his manipulation.
Prospective
E Cohort O(Natural E)
E Experimental O(Assigned E)
Retrospective
Case Control OE
Prospective ORetrospective E
Past
Present
Future
X - Sectional
Design depends on starting point
Types of epidemiological study
