In medical research, study designs are essential to plan any research protocol for experimentation, data collection, data analysis, and publication. Each study design aims to determine different aspects of a disease(s), such as prevalence, incidence, cause, prognosis, or treatment effect. Therefore, it is essential to identify the appropriate analytical study associated with specific objectives.
Scientific study designs are classified as:
- economic evaluations
- Meta-analysis-systematic reviews
Observational studies are not experimentally based, with any controlling factors, and randomization is limited too. These studies include observation of events with no interference or modification of conditions. These are either:
- Descriptive: case report and case series.
- Analytical: cohort (prospective or historical), case-control, and cross-sectional.
Here, we discuss only the analytical study designs.
Analytical study designs:
- Cohort studies:
The word “cohort” is derived from the Latin word “cohors” meaning “unit”. The word was adopted in epidemiology to refer to a set of people monitored for a time. Cohort studies (follow-up studies) are usually longitudinal as they are extended for a while with a cause-and-effect analysis. The participants of the group are usually chosen based on a shared feature. These are usually prospective or retrospective. A prospective study is conducted at present but followed up in the future, i.e., it evaluates the outcomes during follow-up. But a retrospective study (historical) is carried out based on the data collected in the past.
- Case-control studies:
Case-control studies and cohort studies have the same objective of evaluating the relationship between exposure and outcome, but they differ in the sampling strategy. While cohort studies identify the subjects based on the exposure status, case-control studies identify the subjects based on the outcome status. Once the outcome status is identified, the subjects are divided into case and control (randomly selected participants with no adverse outcome). A case-control study is retrospective as the events have already happened at the time of study and cannot be used for calculating relative risk. However, the odds ratio can be measured.
An example can be comparing the smokers (case-study group) and non-smokers (control group) to observe instances of lung disease.
- Cross-sectional studies:
Cross-sectional studies examine and analyze a group of individuals at a specific time point with no further follow-up. The study discusses potential causal relationships between exposure and effects (clinical outcome). For instance, the number of persons is calculated who had lung disease in a specific month of a given year.
Correct identification and reporting of study design is essential for any research. If you found the content informative and educative, please visit https://www.manuscriptedit.com/scholar-hangout/ for more valuable topics. Mail us your queries and comments at firstname.lastname@example.org.
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