In Brief: 

• Cross sectional studies, case-control studies and cohort studies are collectively known as observational studies.
• Observations and not interventions are carried out by the investigator.
• This will act as a quick reference table for researchers and authors.
• This blog tries to discuss each of the observational studies methods  laying emphasis on what their strengths and weaknesses are by comparing them.

Cross sectional studies are used primarily to determine the prevalence of a problem whereas cohort studies involve the study of the population that is both exposed and non-exposed to the cause of disease development agents. Analytical studies that are observational in nature are called as cohort studies and are derived from Latin meaning ‘unit’.  This study can be prospective or retrospective in nature (Barría, 2018).  Case control studies are undertaken with people who are already subjected to the condition or disease that is being studied (Robert & G. Berman, 2015). 

COMPARISONS

• In cross sectional studies, prevalence determines the number of incidences in a given population.  All the required measurements are administered to the set of population at the same time.  Prevalence helps the clinician in knowing the portending value of an investigation and also the likelihood of specific diagnosis.  Questionnaires are mainly used in most of the cross sectional studies.  Cross sectionalstudies are relatively cheap and quick, and allow the researchers to obtain lot of information very quickly.  Due to absence of follow up, less usage of resources are needed to conduct cross sectional studies.  Different variables can be used to run the study.  Researchers working on a project can obtain data on various variables to know how differences in age, sex, income and educational status might correspond with the variable that is critical for the study. They act as a springboard for further studies and research (Hackshaw, 2015).  While studying a public health issue, cross-sectional study helps as a tool in understanding the link between a specific behaviour to a specific illness and acts as a guide for future studies.   For example, in order to understand the influence of exercises on the cognitive function and health of people as they age, researchers can obtain data from people falling into different age bracket as to their exercise routines and their performances in cognitive tests which help researchers obtain the necessary information about the what type of exercises might be beneficial the most for cognitive health of a particular age group and also helps in doing more experimental. But it does have its own limitations.  Relationship between the cause and the outcomes cannot be studied as other variables also affect the link between cause and the outcome.  Accuracy in reports cannot be expected as there might be biases in reports.  There can also be cohort differences as different people might have different experiences that affect their lives due to geographical and demographical regions even though can share the same historical experiences.
• In cohort studies, the results of the study of both the exposed and the non-exposed population are compared to try and find out the link or association between the suspected cause and the disease.  Retrospective cohort studies use the data that is already obtained for other reasons.  Retrospective follow up of the cohort is done.  Prospective Cohort study is suitable for rare exposures.  The incidence rate and the relative risk of the disease can be determined.  A single exposure can determine numerous diseases associated with it.  There is minimization of information and selection biases.  Cause and effect can be established by this type of study.  Retrospective cohort study takes less time to complete in contrast to prospective study.  Several cohorts can be studied.  Incidence data can be estimated.  Limitations include requirement of a huge population to conduct the study for prospective cohort study and longer time required to complete the study.  The outcome of this type of study is largely affected by the loss of people or subjects during the follow up process.  It is not sufficient for the study of diseases that are rare.   It is expensive.  It also has issues related to ethics whereas the Retrospective cohort study has difficulty in identifying the corresponding exposed and non-exposed group to draw comparisons.  Issues of confounding variables are a major weakness and is not suitable for rare diseases. Improper and low quality medical data leads to a lot of errors in the results obtained.
• Case control studies are undertaken with people who are already subjected to the condition or disease that is being studied (Robert & G. Berman, 2015).  Just like taking a ‘history and physical’, the patient is examined and questioned so as to know all those factors and elements that contributed in predisposing the patient to the disease.  Its strengths lies in it being quick and inexpensive.  It is suitable for outcomes that have long latency and fewer subjects for study purpose. Multiple risk factors or exposures can be studied and examined by Case control studies.  Records that already exist can be utilized.  Limitations can be seen as in bias being a major issue.  Validation of information is a problem.  Selecting an appropriate group for comparison can be very difficult.  Determination of exposed and non-exposed disease rate in individuals can be difficult.

Compared to Cohort studies, Cross-sectional and Case Control studies are relative quick and inexpensive.  But in comparison to the other two observational studies, Cohort study is the best way that can be adopted to determine the natural history and incidence of a condition. 

Works Cited

Barría, R. M., 2018. Cohort Studies in Health Sciences. 1 ed. London: Intechopen Limited.

Hackshaw, A., 2015. A Concise Guide to Observational Studies in Healthcare. 1 ed. West Sussex: John Wiley & Sons.

Robert, A. P. & G. Berman, N., 2015. Planning Clinical Research. 1 ed. New York: Cambridge University Press..