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Study type
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Advantages
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Disadvantages
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Cohort
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- Can be performed retrospectively or prospectively; can be used to obtain a true
(absolute) measure of risk (relative risk);
- Can study many disease outcomes; are good for studying rare risk factors.
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- Are time-consuming and costly (especially prospective studies);
- Can study only those risk factors measured at the beginning of the study;
- Can be used only for common diseases;
- May have losses to follow-up.
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Case-control
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- Case-control studies are very useful when a study must be done quickly or
inexpensively or the disease being studied is rare (prevalence <1%) such as
Legionnaires' Disease.
- Many risk factors can be considered and this makes case-control studies useful for
generating hypotheses concerning the causes of a disease [1].
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- Can obtain only a relative measure of risk (odds ratio) (however odds ratios are
similar to risk ratios for rare diseases);
- are subject to recall bias;
- selection of controls may be difficult; temporal relationships may be unclear; can
study only one disease outcome at a time.
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Nested case-control
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- Investigators can test new hypotheses with data that were collected at baseline;
- because the data were collected before the outcome occurred, it is often possible
to know the direction of causation;
- recall bias should not be a problem, because the condition itself would not have
influenced recall;
- design saves both time and money e.g. if expensive baseline blood work
results may only be performed for persons who subsequently participate in the nested
case-control study.
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- Non-diseased persons, from whom the controls are selected, may not be fully
representative of the original cohort, due to death or failure to follow-up cases.
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Case cohort
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- Efficient if several types of cases to compare to same pre-defined cohort
(comparison group)
- Provides an estimate of the risk ratio.
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- Inclusion of "cases" in the comparison group can complicate statistical analysis
compared to case-control studies.
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Seroprevalence/
seroepidemiology studies
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- Detects latent, subclinical infections and carrier states. Can adjust the number of
cases associated with an outbreak and potentially identify other sources of infection.
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- Unlikely to be used in isolation during a Legionnaires' Disease outbreak. Is
usually a retrospective or additional study.
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