4. Cohort studies

Summary

This video module focuses on critical appraisal of cohort studies, emphasizing their importance in healthcare research. It explains why observational studies are necessary when RCTs are not feasible or ethical. The module introduces the concept of risk ratio, illustrates its calculation with an example, and discusses how to interpret it. It also guides viewers on how to appraise cohort studies using a checklist, applying it to a study on lithium treatment and dementia risk. The video concludes with a quiz for viewers to test their understanding.

Takeaways

• 🔍 This video module focuses on the critical appraisal of cohort studies using the CASP approach.
• 🤔 Observational studies are necessary when RCTs are not feasible, unethical, or impractical for rare outcomes.
• 👥 Cohort studies involve identifying participants without an outcome of interest, classifying them by exposure status, and following them over time.
• 🚬 An example given is a cohort study on smoking and lung cancer, where researchers follow participants to see lung cancer development.
• 📊 The risk ratio is a common measure used in cohort studies to express the difference in risk between exposed and unexposed groups.
• 🔢 A risk ratio greater than one indicates an increased risk of disease due to exposure, while less than one suggests a protective effect.
• 📚 The CASP checklist is introduced for critically appraising cohort studies, focusing on validity, results' trustworthiness, and relevance.
• 📝 The study by Gerhardt et al. (2015) on lithium treatment and dementia risk is used as an example to apply the CASP checklist.
• 🧐 Selection bias, measurement bias, and confounding are key issues to consider when critically appraising cohort studies.
• 📈 Statistical models can adjust for confounders to provide a clearer understanding of the relationship between exposure and outcome.
• ⏱ The duration of the follow-up period in cohort studies is crucial to allow the outcome to manifest and to maintain a representative sample.

Q & A

What is the main focus of the fourth video in the critical appraisal series?

The main focus of the fourth video is the critical appraisal of cohort studies using the CASP approach.

Why are observational studies necessary in healthcare research?

Observational studies are necessary because sometimes it's not possible or ethical to conduct randomized controlled trials (RCTs), especially when studying rare outcomes or potentially harmful interventions.

What is the difference between experimental studies and observational studies in terms of researcher involvement?

In experimental studies, researchers manipulate exposures to observe outcomes, whereas in observational studies, they do not manipulate exposures but simply observe what occurs.

What is a cohort study and how does it relate to risk factors and outcomes?

A cohort study is a type of observational study where researchers identify participants without the outcome of interest, classify them by exposure status, and follow them over time to observe the development of the outcome.

How is the risk ratio calculated in cohort studies?

The risk ratio is calculated by dividing the risk of developing the outcome in the exposed group by the risk of developing the outcome in the unexposed group.

What does a risk ratio greater than one indicate in a cohort study?

A risk ratio greater than one indicates that the exposure increases the risk of disease.

What is the purpose of the CASP checklist for critically appraising cohort studies?

The CASP checklist helps assess the validity, trustworthiness of results, and value of relevance in cohort studies.

What is the importance of considering confounding factors in cohort studies?

Confounding factors can distort the relationship between exposure and outcome, either hiding a true relationship or creating a false one. Statistically adjusting for confounders can help estimate their impact.

How does the length of the follow-up period in a cohort study affect the results?

The follow-up period should be long enough for the outcome to manifest. Insufficient follow-up can lead to incorrect measurements of the exposure-outcome relationship.

What does a hazard ratio represent in cohort studies and how does it differ from a risk ratio?

A hazard ratio represents the rate at which an event occurs over time, taking into account the duration of exposure. Unlike the risk ratio, it accounts for the timing of events.

How can the precision of results in cohort studies be assessed?

The precision of results can be assessed by examining the confidence intervals. Narrower intervals indicate higher precision.

What is the role of the CASP checklist in evaluating the believability of results in cohort studies?

The CASP checklist helps evaluate the believability of results by considering factors such as bias, confounding, and the wider body of research.