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KINE 4565: The epidemiology of injury prevention

KINE 4565: The epidemiology of injury prevention. Randomized controlled trials. Overview. Guidelines for student presentations Study design: randomized controlled trials Two examples from the literature. Student presentations.

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KINE 4565: The epidemiology of injury prevention

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  1. KINE 4565: The epidemiology of injury prevention Randomized controlled trials

  2. Overview • Guidelines for student presentations • Study design: randomized controlled trials • Two examples from the literature

  3. Student presentations • The presentation should be 5-7 minutes in length and answer the following questions: • Why did the authors do the study? • What was the study objective? • What was the study design? • What were the results? • What were the strengths and weaknesses? • What can you conclude from this study?

  4. Randomized controlled trials (RCTs) • Well-controlled studies where exposure is randomly allocated • Outcomes are well-documented among all participants • Generally considered the strongest epidemiologic design • Least potential for bias

  5. CONSORT flow diagram

  6. Eligibility criteria Must have the potential to benefit High probability of developing the outcome Safety: Exclude population that will be sensitive to the events (example: pregnant women…) Select individuals likely to comply Exclude individuals with competing risks

  7. Methods of randomization • Most commonly done by the use of computer generated lists of random numbers Ex: 3, 5, 9, 4, 2, … If even ---A If odd-----B Therefore: 1st, 2nd, and 3d receive B 4th and 5th receive A

  8. Methods of randomization • Flip a coin (classic randomization If the sample size is small, the two treatment groups may be unequal. • Blocked randomization Construct blocks of allocation slots to ensure a fairly equal number of subjects in each group

  9. Methods of randomization • Example: Block of 4: alternate treatments could be assigned to subjects ensuring that in each group of 4 2 are intervention and 2 are control. This ensures equal number of participants in each group.

  10. Methods of randomization • Blocks AABB BBAA ABAB BABA ABBA BAAB • Randomly, select block (package) (each package has 4 numbered envelopes). Assign treatments according to the 4 envelopes numbered. • Repeat this until have 100 individuals.

  11. Methods of randomization Problem: • If first two individuals receive A, then know that next 2 will receive B • If first 2 individuals receive B, then know that 2 next individuals will receive A • Always know what the fourth individual will receive

  12. Problem • To avoid this: select different block sizes randomly (permuted block): Package 1: Block size 4 (AABB) Package 2: Block size 6 (AABBAB) Package 3: Block size 4 (ABAB) Package 4: Block size 2 (AB)

  13. Cluster randomization • Used when it is impossible or impractical to do individual randomization • Randomized groups rather than individuals • All the members of the group receive the same intervention • Commonly used groups include hospitals, schools, communities • Analysis must be adjusted to take clustering into account

  14. Analysis • Efficacy: Potential effect of treatment under optimal circumstances: whether treatment can have an effect on outcome. Compare subjects according to the treatment actually received. Exclude subjects who complied poorly, switched over, or withdrew • Effectiveness:Actual effect of treatment in the “real world” of people who comply poorly, or change treatment

  15. Ethical consideration Participation in RCTs Ethical consideration In order for a randomized clinical trial to be ethically justifiable: • none of the trial treatments should be known to be better • No treatment can be known to cause harm at the time the trial begins

  16. Advantages and disadvantages of RCTs Advantages : • Reduced potential for confounding bias • Reduced potential for sample selection bias • Reduced potential for information bias

  17. Disadvantages of RCTs Disadvantages: • May be impractical • May be unethical • Often expensive • May reduce generalizability

  18. What to look for in an RCT • How was randomization done? • Is there any blinding? • Who was included? • Who was excluded? • How were the outcomes assessed? • How was the analysis done? • Can the results be generalized?

  19. Cohort studies • Cohort studies are studies where the intervention and control group are followed over time • Exposure is usually decided by the groups themselves (either based on health behaviours such as smoking or exercise, or geographic location) • Outcomes are measured in both groups

  20. Advantages of cohort studies • Less expensive than RCTs because the groups are not allocated • Fewer ethical considerations because groups can self-select • Able to look at the natural progression of the disease or outcome

  21. Disadvantages of cohort studies • Can be expensive to follow participants over time • Not economical for rare outcomes • Potential for confounding bias if there are other variables associated with choosing to be in one group • Sometimes the outcomes are not measured the same in both groups

  22. What to look for in a cohort study • How were the exposure groups defined? • Are there potentially confounding variables? • What were the losses to follow up in each group, and were they similar? • How was outcome assessed, and was it the same for both groups?

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