A Roman legion was made up of ten cohorts.
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 was usually composed of a single type of soldiers. A legion was formed with ten cohorts, which were numbered from I to X. The cohorts, in turn, were made up of three maniples (made up of two centuries ). Cohort I , on the other hand, had exceptional characteristics and was made up of five double centuries.
There were, outside the army, civil security cohorts, such as the urban cohorts (which were responsible for daytime security) and the vigilum cohorts (dedicated to ensuring nighttime security).
Cohort as series or set
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 period of time.
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.
For demographics, a cohort is a group of individuals who share something in a certain time period.
Frequency of a phenomenon in groups of people
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 given risk factor. To select the individuals who are part of the study, the presence of certain characteristics and exposure to said factor is taken into account.
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;
* track 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 uncommon exposure factors ;
* analyze the different effects that may arise from said exposure;
* whenever it is considered 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 at a given time) and the relative risk (the ratio between the risk of the group with the exposure factor and that of the group without it);
* clearly define the sequence of events of interest, such as exposure-disease;
* avoid making a perceptual error known as survivorship 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:
* normally 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 analysis of rare diseases or events.