I am going to answer the sample USMLE Step 1 Questions with Explanation. These questions are available at USMLE.org
Investigators conduct a study that evaluates the effect of finasteride on the incidence of prostate cancer in 500 patients. The investigators recruit an additional 1000 patients for the study.
Which of the following effects will this have on the research study?
(A) Greater chance of a Type I error
(B) Greater chance of a Type II error
(C) Less chance of a Type I error
(D) Less chance of a Type II error
(E) Impossible to predict
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Answer
Increasing the sample size in a study generally improves its statistical power, which is the likelihood of detecting a true effect if one exists. A larger sample size reduces the probability of a Type II error (failing to reject a false null hypothesis, or missing a true effect). It does not directly affect the Type I error rate, typically set by the significance level (e.g., α = 0.05).
The correct answer is D