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KINE 4565: The epidemiology of injury prevention Randomized controlled trials

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

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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?

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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

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CONSORT flow diagram

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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

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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

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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

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Methods of randomization oExample: 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.

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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.

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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

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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)

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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

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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 Analysis

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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

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Advantages and disadvantages of RCTs Advantages : –Reduced potential for confounding bias –Reduced potential for sample selection bias –Reduced potential for information bias

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Disadvantages: – May be impractical –May be unethical –Often expensive –May reduce generalizability Disadvantages of RCTs

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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?

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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

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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

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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

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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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