WBR0435

Author	[[PageAuthor::Rim Halaby, M.D. [1], Alison Leibowitz [2] (Reviewed by Alison Leibowitz)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biostatistics/Epidemiology
Sub Category	SubCategory::Renal
Prompt	[[Prompt::A researcher conducts a cross-sectional study to identify factors that are associated with hemodialysis adequacy in a group of 90 patients undergoing hemodialysis. Statistical analysis regarding the urea reduction rate (URR), reveals a p-value of 0.12 at a 95% confidence interval. Which of the following modifications will most likely increase the statistical power of the association between URR and hemodialysis adequacy in this study?]]
Answer A	AnswerA::Recruiting more hemodialysis patients to the study
Answer A Explanation	AnswerAExp::Recruiting more patients, who fit the inclusion criteria, can increase the statistical power of the study.
Answer B	AnswerB::Recruiting 90 peritoneal dialysis patients to the study
Answer B Explanation	AnswerBExp::Since the study does not involve peritoneal dialysis patients, adding those to the study is not appropriate and will most likely limit the study’s statistical power.
Answer C	AnswerC::Changing the confidence interval to 92%
Answer C Explanation	AnswerCExp::Decreasing the confidence interval will most likely increase the associated factors; but the statistical power of the study will not increase.
Answer D	AnswerD::Repeating all measurements of urea reduction rate for the 90 patients who are recruited
Answer D Explanation	AnswerDExp::Repeating measurements will test the precision of the study’s measurements. Since measurements were described as precise in the first place, the statistical power of the study is likely not affected.
Answer E	AnswerE::The statistical power of the study cannot be changed
Answer E Explanation	AnswerEExp::The statistical power of the study can be changed if the sample size is increased.
Right Answer	RightAnswer::A
Explanation	[[Explanation::Statistical power of a study is defined as: Power = (1-β), where β is the type II error (perceiving there is no effect when there actually is). The power of the study is dependent on the sample size of enrolled patients. Adding more hemodialysis patients to the study will increase the power of the study. Educational Objective: Statistical power of a study is defined as: Power = (1-β), where β is the type II error. Power can be increased when the sample size of the enrolled patients increases. References: First Aid 2014 page]]
Approved	Approved::Yes
Keyword	WBRKeyword::urea reduction rate, WBRKeyword::URR, WBRKeyword::hemodialysis, WBRKeyword::statistical power, WBRKeyword::type II, WBRKeyword::error, WBRKeyword::sample size, WBRKeyword::study, WBRKeyword::equation
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