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Review Question - QID 211200

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QID 211200 (Type "211200" in App Search)
A randomized controlled trial is undertaken to investigate whether tourniquet use increases cement penetration during total knee arthroplasty. Approximately 40% of the patients that were initially randomized to the "no tourniquet" group had tourniquets placed intraoperatively due to difficulty with visualization. Intent-to-treat analysis was conducted and the results showed no difference in the rates of cement penetration. What statistical term best applies if these results are accepted at face value?

alpha error

23%

466/2060

beta error

53%

1101/2060

1 - alpha

6%

131/2060

1 - beta

8%

165/2060

kappa statistic

8%

161/2060

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The null hypothesis in this randomized controlled trial is that there is no difference in cement penetration during TKA with or without tourniquet use. As there was significant crossover (tourniquet use in the "no tourniquet" cohort), accepting the null hypothesis when it is false would result in beta (type 2) error.

In hypothesis testing, the assertion that the observed findings did not occur by chance alone but rather occurred because of a true association between variables is confirmed or rejected. By convention, the null hypothesis suggests that there is no significant association between variables while the alternative hypothesis suggests that there is a significant association. Alpha (type 1) error occurs when the null hypothesis is rejected when it is, in fact, true (false positive effect). Beta (type 2) error occurs when the null hypothesis is accepted when it is, in fact, false (false negative effect).

Kocher et al. reviewed power analyses, statistical errors, and the concept of statistical power. They discuss that beta represents the chance of a type II error, while alpha represents the chance of a type I error, and that conventionally beta is set at 0.2 and alpha at 0.05. The authors recommended that when a study observes no difference, the power of the study, or (1 - beta), should be reported.

Lochner et al. investigated the rates of beta error in randomized controlled trials in orthopedic trauma. They reported a 90% beta error rate in these trials, which exceeds accepted standards. The authors recommended that future authors perform pre-study power and sample-size calculations to reduce these rates.

Illustration A shows a Bayesian analysis table demonstrating the relationship between alpha, beta, and the null hypothesis.

Incorrect Answers:
Answer 1: The alpha (type 1) error occurs when the null hypothesis is rejected when it is, in fact, true (false positive effect). In other words, a difference is found by chance when there is not one. In this scenario, the null hypothesis is accepted.
Answer 3: (1 - alpha) corresponds to the probability of finding a true negative, i.e. the null hypothesis is correctly accepted.
Answer 4: (1 - beta), or power, is the probability of finding a significant association if one truly exists.
Answer 5: The kappa statistic is used to measure inter-observer and intra-observer reliability.

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