Cohort, from the Latin cohors, is a term with two different meanings. On the one hand, it is a tactical unit of the Roman army that, throughout history, had different conformations. On the other hand, cohort is a series, a set, or a number.
A Roman cohort, therefore, was an army unit that generally consisted of only one type of soldier. A legion was formed with ten cohorts, who were numbered from the I to the X. The cohorts, in turn, were made up of three maniples (made up of two centuries). The Cohort I, however, had exceptional characteristics and consisted of five double centuries.
There were, outside the army, civil security cohorts, such as urban cohorts (which were in charge of daytime security) and vigilum cohorts (dedicated to ensuring night security).
As a set or series, the notion of cohort is used in demography, epidemiology, and education. A cohort is a group of people who share the same event within a certain time period.
This means that a cohort, for example, can be made up of all the people born in a city X between 1970 and 1972. Another example of a cohort is the group of students who begin their primary studies in the same year and who, therefore, should complete them together. In this sense, cohort is synonymous with promotion.
For biology, on the other hand, a cohort is also a set of individuals, in this case related in a taxonomic superorder.
The objective of a cohort study (which is considered analytical, observational, epidemiological and prospective longitudinal) is to compare the frequency of a disease or a particular phenomenon between two groups of people, provided that only one of them is exposed. to a certain risk factor. To select the individuals who are part of the study, the presence of certain characteristics and the exposure to said factor are taken into account.
According to DigoPaul, some of the fundamental points of a cohort study are the following:
* identify and select healthy individuals within a population (this group is called a sample);
* check if the risk factor is present in the sample, measuring the exposure variables;
* keep track of the cohort;
* Measure the outcome variables to verify the presence of the disease in question.
Among the advantages of a cohort study, it is correct to say that it allows:
* study unusual exposure factors;
* analyze the different effects that may arise from such exposure;
* Whenever it arises from the beginning of the study, simultaneously observe the effects of more than one exposure;
* estimate the incidence (the number of new cases of a disorder in a population and at a given time) and the relative risk (the ratio between the risk of the group with the exposure factor and that of the one without it);
* clearly define the sequence of events of interest, such as exposure-disease;
*avoid making a perception error known as survival bias, which is characterized by ignoring results that do not pass a certain process;
* select subjects more efficiently;
* effectively control the measures.
On the other hand, the following drawbacks are also noted:
* usually requires samples of a considerable number;
* does not offer great efficiency when latency periods are very long;
* usually requires a significant investment of time and money;
* not recommended for the analysis of diseases or rare events.