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Definition ||Advantages ||Disadvantages
One of the advantages of cohort analysis is that the study design does not require strict random assignment of subjects, which is, in many cases, unethical or improbable. As in the case of smoking vs. non-smoking cohort study, random assignment is not a feasible or ethical alternative. (Who wants to be assigned to a smoking group if he/she is non-smoker?). Cohort analysis is an appealing and useful technique because it is highly flexible. It provides insight into the effects of maturation and social, cultural, and political change. In addition, it can be used with either original data or secondary data. In some instances, a cohort analysis can be less expensive than experiments or surveys. One of the most difficult tasks in cohort studies is to assess whether associations between cohort and dependent variables derived from the studies are of a causal nature or not. Cohort studies are subject to the influence of factors over which the investigators most often do not have full control, and that findings from these studies are more open to threats to validity than those of studies with an experimental research design Because of the lack of randominization in the cohort design, the two groups may differ in ways other than in the variable under study. For example, if the subjects who smoke tend to have less money than the non-smokers, and thus have less access to health care, that would exaggerate the difference between the two groups. The other problem with cohort studies is that they can end up taking a very long time, since the researchers have to wait for the conditions of interest to develop. Researchers are, of course, anxious to have meaningful results as soon as possible, but another disadvantage with long studies is that things tend to change over the course of the study. People die, move away, or develop other conditions, new and promising treatments arise, and so on. If the remaining cohort members differ in regard to the variable under they study, the variation in the cohort study may simply reflect this change. (for more information see Selection-Mortality threat) It is therefore imperative that findings from cohort studies are critically scrutinized before any judgement of causality is made. |
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