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Observational studies. Is it a cohort, case series, or cross-sectional study?

Observational studies. Is it a cohort, case series, or cross-sectional study?

In our previous article, we introduced the types of research that we conduct in the scientific community. Observational studies can be case series, cohort, case-control, or cross-sectional studies. Let’s understand what each of these means?

Case series (reports) describe a character in a group of people, patients, or individuals and report it. Case series can take place at an instance or over some time. The aim is to analyse a particular phenomenon and report the findings. We commonly use them to identify fascinating observations to assess their feasibility for future planning or research. You can access case series from BMJ Case Reports, as well as other data platforms.

Related:  Types of Research. Is it an observational or experimental study?

For case-control studies, we select subjects basing whether they possess (cases) or lack (control) a particular trait, outcome, or disease. We look back in time (retrospective) to check for characteristics (variables and risk factors) that differ between groups. We then attempt to ascertain the relationship between them, say the exposure of risk actors and the disease, smoking and lung cancer. We can include two or more patient groups. The major drawback is confounding. Confounding is a false association between the exposure and the outcome; for example, drinking coffee in quantities is associated with an increased risk of heart disease.

In cross-sectional studies, we identify a population or subpopulation and not individuals. We conduct them at a particular point in time and measure multiple variables across different groups concurrently. We usually organise them in the form of surveys. They are quick, easy, and cost-effective. They are the mainstay of collecting information. They can be a part of other study designs, say, case-series or case-control studies. The aim is to ascertain the prevalence of an outcome or variable. Their drawbacks are mainly bias and the inability to separate a cause from an effect. It lies in how participants respond to questions. For example, a participant can decide to reply yes to a particular set of questions, a feature that will distort the data findings. Because these studies occur at a certain point in time, it is impractical to study a relationship between a risk factor and the disease.

Lastly, cohort studies: a cohort is a group of participants that possess a common characteristic or trait. We begin cohort studies by identifying participants with a common characteristic – disease or risk factor, for example, smokers – and observe them over time. We can do this either retrospectively or prospectively. In a retrospective cohort study, we use existing data to identify a population and exposure status. On the other hand, in a prospective study, we identify participants with a common trait and their exposure status at the beginning of the research and follow them up.

In our next article, we explain what experimental studies entail. You can enrol for an online course to gain a deeper insight into observational studies from .

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MBChB (MUK), Graduate Fellow, Department of Physiology, Makerere University Founder and Content Creator Peer reviewer, Associate Editor

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