In a cohort study, an investigator selects two or more groups (cohorts) of people. The identified groups differ by the fact that one group of people is affected by the studied risk factor (exposed group), and the other one – does not (unexposed group) (Aschengrau & Seage, 2014). Thereafter, they are compared with each other for the appearance of the disease (outcome). Thus, the investigator can understand how to study the risk factors associated with subsequent diseases (outcomes).
The cohort study has a number of obvious advantages. First of all, there is the evident simplicity of the question, which defines the purpose of the study: whether people become ill if they are exposed to certain factors? Moreover, it is possible to determine in advance what data is needed and accurately collect it (Rothman, 2012). In addition, the mentioned study design allows evaluating a wide range of outcomes related to the influence of a single factor, as well as a variety of factors leading to the particular outcome.
However, the cohort study can be inefficient and expensive in case the studied outcome is rare and requires including plenty of subjects. Furthermore, the outcome might be remote in time, so the participating entities may be lost, and the results of the study might become irrelevant.
Studies of this type are the most suitable in the examination of rare diseases as cohort studies are not applicable due to the need for the formation of relatively large cohorts in order to collect a sufficient number of cases. The theory of case-control studies stems from the theory of cohort studies. In other words, the latter could be described as an attempt to reconstruct the cohort study after the disease has occurred. The case-control study starts from the disease assessment in ill subjects (cases) and healthy individuals (controls).
Among the benefits of case-control studies, one might note relative cheapness along with pace as sometimes it is important to get a quick answer. What is more, it is appropriate to explore rare diseases. The case-control study can examine a number of factors at the same time, yet only for one outcome.
Nevertheless, there are also some disadvantages of the case-control study. It is not always possible to calculate the risk indicators. There is a possibility of bias in the selection of cases and controls and in the collection of information. Problems arising from the case-control research might be also associated with unavailable or inaccurate data.
Thus, the selection of the study design primarily depends on the specific tasks, yet it is largely determined by the available resources and timing (Burt & Eklund, 2005). Knowing the capabilities of different methods, namely, their strengths and weaknesses allow the optimal planning of an epidemiologist study.
Pretending I am working in the field of dental public health, I would apply the observational study design of the cohort study to investigate the issue of caries among children. In particular, I would study the following research question: whether breastfeeding reduces the risk of caries among children. In this case, I would need to collect data including the age of participants, background information, genetic history, nutrition, and other information concerning participants. I prefer the above method as the cohort study includes new and accurately diagnosed cases such as clinical, radiological, morphological, and other confirmations of the diagnosis.
Aschengrau, A., & Seage, III, G. R. (2014). Essentials of epidemiology in public health (3rd ed.). Sudbury, MA: Jones and Bartlett.
Burt, B. A., & Eklund, S. A. (2005). Dentistry, dental practice, and the community (6th ed.). St. Louis, MO: Elsevier Saunders.
Rothman, K. J. (2012). Epidemiology: An Introduction (2nd ed.). New York, NY: Oxford University Press.