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Presented at the Mission Academy Research Summer School on July 15, 2025; by Dr Omar Hasan Kasule Sr MB ChB (MUK), MPH (Harvard), DrPH (Harvard), Professor of Epidemiology and Chairman of the Institutional Review Board at King Abdullah bin Abdulaziz University Hospital, Princess Noura University.
Preliminaries of Study Design 1: Identifying the Population:
There are basically four ways of identifying populations for epidemiological studies:
► Geopolitical areas (village, town, district, etc.),
► Lists of households,
► Restricted or institutional, such as special registers and schools, and Health insurance databases.
Preliminaries of Study Design 2: Selecting the Population:
Four considerations are made in the process of population selection:
► Representativeness,
► Accessibility,
► Accuracy of the population denominator,
► The desired study size.
Preliminaries of Study Design 3: Sample Selection:
► In reality, we study samples and not populations.
► The samples represent the population.
► The samples may be selected scientifically to be random or may be non-probability: convenience, quota, or purposive.
5 Main Study Designs:
► Observational studies
§ Cross-sectional study design.
§ Case-control study design.
§ Follow-up study design.
► Experimental studies
§ Randomized clinical trials.
§ Randomized community trials.
Choice of Study Design:
► Each type of design is preferable in a given set of circumstances.
► Cross-sectional design is both the preliminary design and a source of health planning epidemiological data.
► The case-control design is best for etiological studies of rare diseases. It is usually a preliminary study to be confirmed, followed by a follow-up or experimental study.
► The follow-up design is best for etiological studies because the time sequence is known. It is also preferred for common, severe, and easily observed diseases that only need a short follow-up.
► The experimental design is used for the final proof of causality or efficacy of the intervention.