(1)Case control/Case reference
(B)Experimental Studies/Intervention Studies
(1)Randomized controlled trials/Clinical trials
(2)Field trials/Community intervention trials
Descriptive Studies: Epidemiological investigations often start with eth case reports and evolve to become a series of cases. The procedure involved in descriptive studies are defining population and the disease under study, describing the disease by time, place and person, measuring the disease (in terms of incidence/prevalence) comparing with known indices and formulating an etiological hypothesis. Descriptive epidemiology may use a cross-sectional or longitudinal design to obtain estimates of the cross section of the population at one point in time. In longitudinal study examinations are repeated in the same population over a prolonged period of time by means of follow-up examination. Analytical Studies: Here the objective is not to formulate, but to test hypotheses. In contrast to descriptive studies that look at entire populations, in analytical studies, the subject of interest is the individual within the population. Here the comparison is made between cause/study group and control groups. Analytical studies may be observational or experimental. Observational Studies: In an Observational study, the epidemiologist assigns subjects to case and comparison groups. This assignment may take place after an event has occurred or before an event has happened. Observational studies are carried out to determine whether or not the statistical association exits between a disease and a suspected cause, and if one exists the strength of association.
Cohort study: The starting point of a cohort study is the recording of healthy subjects with and without exposure to the putative agent or the characteristic being studied. Individuals exposed to the agent under study (index subjects) are followed over time and...