The cohort study is one that follows a large group of people and assesses, for example, the health effects of the risk factors to which they are exposed. The capacity of these studies is based on a rigorous methodology to avoid any biases, errors in data collection or in the interpretation of the results.
A cohort study is carried out, for example, with the objective of knowing the causes of a disease and establishing the relationship between risk factors and health outcomes.
This type of study is carried out by comparing a population exposed to a disease with unexposed individuals. The analysis or follow-up is carried out over time until the following occurs:
- The disease occurs
- Study subject dies
- Study subject disappears during study follow-up
- The study ends
You may also be interested in knowing: What is a longitudinal study?
Cohort study types
There are several types of Cohort study:
Prospective study: They are planned in advance and carried out in a future period of time. In this study, individuals do not have the disease, but it is observed over a period of time to observe the frequency of its manifestation in different groups.
Retrospective study: In this type of study, existing data are examined in order to identify risk factors for particular diseases. Interpretations are limited as it is not possible to go back in time and gather the missing information.
I recommend you read this article on how to conduct Health Care Surveys.
Advantages of conducting a cohort study
- It is possible to study elements that are not identified or that may be strange.
- It allows us to observe a great variety of exposed effects.
- It is possible to observe the effects of a disease at the same time.
- It allows estimating the levels of cases presented and the relative risks.
- Select study subjects carefully.
Some of the disadvantages of conducting a cohort study are the following:
- They make it difficult to find signs of some rare diseases.
- Generally, these types of studies cannot identify the causes of a disease that appears suddenly.
- Studies are very expensive and take many years to produce results.
- They offer clues to the causes of a disease, but not definitive proof.
- Research can produce biased results because participants may disappear or die.
Cohort study example
A town in Latin America experienced an outbreak of salmonellosis. Over a long period of time, health officials were able to observe an unusually large number over several days.
When conducting the descriptive epidemiological study and the interviews that generated the hypotheses that the people who presented the disease had attended a parents’ lunch at a local school. In which, each attendee brought a dish prepared at home. The study revealed that the outbreak originated from that fact. However, they had to know which specific dish had caused the incident.
Below is a description of the study:
- Incubation period: 1 to 3 days
- Symptoms: Diarrhea, fever, abdominal pain, vomiting, headache, chills.
- Duration: 4-7 days
- Sources: Contaminated eggs, poultry, dairy, unpasteurized juices, fruits and vegetables.
Laboratory result: Stool cultures
58% of the attendees had developed symptoms consistent with the case definition. Of these, 45 attendees agreed to complete a questionnaire about the foods they had eaten for lunch.
For each dish served at lunch, the researchers compared the incidence of salmonellosis among those who ate a particular dish and those who had not eaten that dish.
The results revealed that 23 attendees recalled having eaten the cheese snack, and 16 of them developed salmonellosis, that is, an incidence of 70%. There were 22 attendees who did not recall having eaten the cheese appetizer, and 9 or these developed symptoms of salmonellosis, with an incidence of 41%.
Types of questions for information related to the salmonellosis outbreak include:
- What are the foods you ate in the last 48 hours?
- Was the food you ate prepared at home?
- Did the food you eat have a cleaning process?
- Has the food you consumed not yet reached the expiration date?
- What are your current symptoms?
- Finally, discover how to apply a health survey with this article that we have for you.
The Cohort study design is a good choice when it comes to the outbreak in a relatively small and well-defined population.