Question

Discuss the various options for sampling and cohort formation within epidemiologic cohort studies. As a practicing epidemiologist, how would you go about selecting the best sampling and cohort formation options for a particular study?

Answer 1

In epidemiology which is the study of distribution of health and disese condition, there are are types of observational studies; 1) cohort studies, 2) case-control studies, and 3) cross-sectional studies.
In cohort study, cohort means for a set of people studied over a period of time. In
epidemiology, we can say it measures the disease occurance and its association with an exposure over a period of time hence it is a temporal framwork which assess the cause and effect relationship.

Types of Cohort Studies
1) Prospective cohort
In a prospective study, the investigator carried out the study present time into the future. After defining a study population, the investigator determines the exposure status of the cohort and select the non-cases then follow up a period of time.
2) Retrospective cohort study
In a retrospective study, the investigator study the past events or outcomes for a cohort selected based on present exposure status. The investigator study the all the exposed and nonexposed persons and then determines their current exposure status.

Sampling framwork:

In cohort study, a sample is selected for a longitudinal assessent of exposure status. The sampling framework represent a well defined population of interest. For example, these population may be geographically defined or some particular organization based. These population are based on probability sampling where the subjects of the population get an equal opportunity to be selected. While the exact sampling may varies as per interst of investigator. For example door to door recruitment, telephonic recruitment, based on identification card such as driving licence or voter ID card. The one of the good sampling approach to minimize the cost and maximize the recruitment may be by visiting the sites (e.g hospital) avoiding door to door visit.