- 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).
- 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.
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