Types of Potential Bias in Cohort Studies: Most
1. Selection bias: select participants
2. Information bias:
- Collect different quality and extent of information from exposed and not exposed groups
- Loss to follow-up differs between exposed and not exposed (or between disease and no disease)
Advantages of cohort studies
• Can directly measure incidence in exposed and unexposed groups
• Provides the true relative risk
• Cohort studies are well suited for rare exposures
• The temporal relationship exposure‐disease is clear
• Cohort studies can be less subject to selection biases (when the outcome is not known; prospective studies)
• Cohort studies can examine multiple outcomes for a single
Exposure
Disadvantages of cohort studies
• They require a large sample size
• The period between exposure and disease (latency) can be very long
• Cohort studies can be very costly and time-consuming
• There can be a loss to follow-up, which may result in bias
• Exposures may change over time, which can be hard to measure
• It can be difficult to collect information on multiple exposures
• If an exposure is deleterious, ethical considerations need to be taken into account
2) Case – control studies: investigated associations between the exposure to a risk factor and the occurrence of disease