WBR0435: Difference between revisions

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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}}
|QuestionAuthor={{Rim}}, {{AJL}} {{Alison}}
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Biostatistics/ Epidemiology
|MainCategory=Biostatistics/ Epidemiology
Line 20: Line 20:
|MainCategory=Biostatistics/ Epidemiology
|MainCategory=Biostatistics/ Epidemiology
|SubCategory=Renal
|SubCategory=Renal
|Prompt=A researcher is conducting a cross-sectional study to identify factors that are associated with hemodialysis adequacy in a group of 90 patients undergoing hemodialysis.  After data collection, statistical analysis reveals that after precise measurement of the urea reduction rate (URR), URR is associated with hemodialysis adequacy with a p-value of 0.12 at a 95% confidence interval.  Which of the following modifications will most likely increase the power of the association in the study conducted by this researcher?
|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?
|Explanation=Power of the study is defined as: Power = (1-β), where β is the type II error – defined as perceiving there is no effect when in fact there is.  Power of the study is dependent on the size of the study population.  As such, adding more [[hemodialysis]] patients to the study will most likely increase the power of the study.


Educational Objective:
|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.
Power of the 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.


|EducationalObjectives= 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
|AnswerA=Recruiting more hemodialysis patients to the study  
|AnswerA=Recruiting more hemodialysis patients to the study  
|AnswerAExp=Recruiting more patients to the study that fit the inclusion criteria can increase the power of the study.
|AnswerAExp=Recruiting more patients, who fit the inclusion criteria, can increase the statistical power of the study.
|AnswerB=Recruiting 90 peritoneal dialysis patients to the study
|AnswerB=Recruiting 90 peritoneal dialysis patients to the study
|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 power.
|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.
|AnswerC=Changing the confidence interval to 92%
|AnswerC=Changing the confidence interval to 92%
|AnswerCExp=Decreasing the confidence interval will most likely increase the associated factors; but the power of the study will not increase.
|AnswerCExp=Decreasing the confidence interval will most likely increase the associated factors; but the statistical power of the study will not increase.
|AnswerD=Repeating all measurements of urea reduction rate for the 90 patients who are recruited
|AnswerD=Repeating all measurements of urea reduction rate for the 90 patients who are recruited
|AnswerDExp=Repeating measurements will test the precision of the study’s measurements.  Since measurements were described as precise in the first place, the study’s power is not expected to be affected.
|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.
|AnswerE=Power of the study cannot be changed
|AnswerE=The statistical power of the study cannot be changed
|AnswerEExp=Power of the study can in fact be changed if the sample size is increased.
|AnswerEExp=The statistical power of the study can be changed if the sample size is increased.
|RightAnswer=A
|RightAnswer=A
|WBRKeyword=urea reduction rate, hemodialysis, power, type II, error, sample, size, confidence, interval
|WBRKeyword=urea reduction rate, URR, hemodialysis, statistical power, type II, error, sample size, study, equation,
|Approved=No
|Approved=Yes
}}
}}

Revision as of 15:30, 22 July 2014
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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