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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.
HEALTH SURVEYS - 1:► Study of the status of disease and its causes at a point in time.
► Cross-sectional studies are used in community diagnosis, preliminary study of disease etiology, assessment of health status, disease surveillance, public health planning, and program evaluation.
► Cross-sectional studies have the advantages of simplicity and rapid execution to provide rapid answers.
► The disadvantages are inability to study etiology because the time sequence between exposure and outcome is unknown, inability to study diseases with low prevalence, high respondent bias, poor documentation of confounding factors, and over-representation of diseases of long duration.
HEALTH SURVEYS - 2:► Surveys involve more subjects than the usual epidemiological sample used for measurement of health and disease, assessment of needs, assessment of service utilization, and care.
► Planning of surveys includes literature survey, stating objectives, identifying and prioritizing the problem, formulating a hypothesis, defining the population, defining the sampling frame, determining sample size and sampling method, training study personnel, considering logistics (approvals, manpower, materials and equipment., finance, transport, communication, and accommodation), preparing and pre-testing the study questionnaire. Surveys may be cross-sectional or longitudinal.
CASE-CONTROL DESIGN:► The household is the usual sampling unit.
► Existing data may be used, or new data may be collected using a questionnaire (postal, telephone, diaries, and interviews), physical examinations, direct observation, and laboratory investigations. The structure and contents of the survey report are determined by potential readers. The report is used to communicate information and also to apply for funding.
FOLLOW-UP DESIGN:► The case-control study is popular because of its low cost, rapid results, and flexibility. It uses a small number of subjects.
► Cases are sourced from clinical records, hospital discharge records, disease registries, data from surveillance programs, employment records, and death certificates.
► Controls must be from the same population base as the cases and must be like cases in everything except having the disease being studied.
RANDOMIZED DESIGN: COMMUNITY TRIALS - 1:► A follow-up study (also called a cohort study, incident study, prospective study, or longitudinal study) compares disease in exposed groups to disease in non-exposed groups after a period of follow-up.
► Follow-up can be prospective (looking forward), retrospective (looking backward), or ambispective (combining both forward and backward follow-up).
RANDOMIZED DESIGN: COMMUNITY TRIALS - 2:► A community intervention study targets the whole community and not individuals.
► The Salk vaccine trial carried out in 1954 had 200,000 subjects in the experimental group and a similar number in the control group.
► The aspirin-myocardial infarction study was a therapeutic intervention that randomized 4524 men to two groups. The intervention group received 1.0 gram of aspirin daily, whereas the reference group received a placebo.
RANDOMIZED DESIGN: CLINICAL TRIALS:► The Women’s Health Study involved the randomization of 40,000 healthy women into two groups to study the prevention of cancer and cardiovascular disease. One group received vitamin E and low-dose aspirin. The other group received a placebo.
► The alpha tocopherol and beta carotene cancer prevention trial randomized 19,233 middle-aged men who were cigarette smokers.
► The aim of randomization in controlled clinical trials is to make sure that there is no selection bias and that the two series are as alike as possible by randomly balancing confounding factors.
► Patients are allocated randomly either to the new drug or the old drug, and rates of cure or improvement are compared.