Advantages and
Disadvantages of Case-Control Studies
Advantages:
- They are efficient for rare diseases or diseases with a long latency period between exposure and disease manifestation.
- They are less costly and less time-consuming; they are advantageous when exposure data is expensive or hard to obtain.
- They are advantageous when studying dynamic populations in which follow-up is difficult.
Disadvantages:
- They are subject to selection bias.
- They are inefficient for rare exposures.
- Information on exposure is subject to observation bias.
- They generally do not allow calculation of incidence (absolute risk).
Advantages & Disadvantages of Cohort Studies
Advantages
Clarity of Temporal Sequence (Did the exposure precede the outcome?): Cohort studies more clearly indicate the temporal sequence between exposure and outcome, because in a cohort study, subjects are known to be disease-free at the beginning of the observation period when their exposure status is established. In case-control studies, one begins with diseased and non-diseased people and then acertains their prior exposures. This is a reasonable approach to establishing past exposures, but subjects may have difficulty remembering past exposures, and their recollection may be biased by having the outcome (recall bias).Allow Calculation of Incidence: Cohort studies allow you to calculate the incidence of disease in exposure groups, so you can calculate:
·
Absolute risk (incidence)
·
Relative risk (risk ratio or rate ratio)
·
Risk difference
·
Attributable proportion (attributable risk %)
Facilitate
Study of Rare Exposures: While a cohort design can be used to investigate common exposures
(e.g., risk factors for cardiovascular disease and cancer in the Nurses' Health
Study), they are particularly useful for evaluating the effects of rare or
unusual exposures, because the investigators can make it a point to identify an
adequate number of subjects who have an unusual exposure, e.g.,
·
Exposure to toxic chemicals (Agent Orange)
·
Adverse effects of drugs (e.g., thalidomide) or
treatments (e.g., radiation treatments for ankylosing spondylitis)
·
Unusual occupational exposures (e.g., asbestos,
or solvents in tire manufacturing, )
Allow
Examination of Multiple Effects of a Single ExposureAvoid Selection Bias at Enrollment
Disadvantages of Prospective Cohort Studies
1. You may
have to follow large numbers of subjects for a long time.
2. They
can be very expensive and time consuming.
3. They
are not good for rare diseases.
4. They
are not good for diseases with a long latency.
5. Differential
loss to follow up can introduce bias.
Disadvantages of Retrospective Cohort Studies
1. As with
prospective cohort studies, they are not good for very rare diseases.
2. If one
uses records that were not designed for the study, the available data may be of
poor quality.
3. There
is frequently an absence of data on potential confounding factors if the data
was recorded in the past.
4. It may
be difficult to identify an appropriate exposed cohort and an appropriate
comparison group.
5. Differential
losses to follow up can also bias retrospective cohort studies.
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References
1. Song,
J. and Chung, K. Observational Studies: Cohort
and Case-Control Studies. Plastic and Reconstructive
Surgery. 2010 Dec;126(6):2234-2242.
2. Ury
HK. Efficiency of case-control
studies with multiple controls per case: Continuous or dichotomous data. Biometrics. 1975
Sep;31(3):643–649.
3. von
Elm E, Altman DG, Egger M, Pocock SJ, Gøtzsche PC, Vandenbroucke JP; STROBE
Initiative. The
Strengthening the Reporting of Observational Studies in Epidemiology (STROBE)
statement: guidelines for reporting observational studies. Lancet 2007
Oct;370(9596):1453-14577. PMID: 18064739.
4. Boston
University School of Public Health. Advantages and disadvantages of
case-control studies; 2016 Sep. access 22/06/2019.
5. Boston
University School of Public Health. Advantages and disadvantages of cohort
studies; 2016 Sep. access 22/06/2019.
