title: Power estimation for multireader ROC methods an updated and unified approach.
abstract: OBJECTIVE
  We describe a step-by-step procedure for estimating power and sample size for planned multireader receiver operating characteristic (ROC) studies that will be analyzed using either the Dorfman-Berbaum-Metz (DBM) or Obuchowski-Rockette (OR) method. This procedure updates previous approaches by incorporating recent methodological developments and unifies the approaches by allowing inputs to be conjectured parameter values or outputs from either a DBM or OR pilot-study analysis.
  
  
  METHODS
  Power computations are described in a step-by-step procedure and the theoretical basis for the procedure is described. Updates include using the currently recommended denominator degrees of freedom, accounting for different pilot and planned study normal-to-abnormal case ratios, and a new method for computing the OR test-by-reader variance component.
  
  
  RESULTS
  Using a real dataset we illustrate how to compute the power for two planned studies, one having the same normal-to-abnormal case ratio as the pilot study and the other having a different ratio. In a simulation study, we show that the proposed procedure gives mean power estimates close to the true power.
  
  
  CONCLUSIONS
  Application of the updated procedure is straightforward. It is important that pilot data be comparable to the planned study with respect to the modalities, reader expertise, and case selection. Variability of the power estimates warrants further investigation.
authors.affiliation: Iowa City VA Medical Center, IA 52246-2208, USA. steve-hillis@uiowa.edu
authors.forename: Stephen L
authors.initials: SL
authors.lastname: Hillis
authors.forename: Nancy A
authors.initials: NA
authors.lastname: Obuchowski
authors.forename: Kevin S
authors.initials: KS
authors.lastname: Berbaum
mesh_terms: D000704:Analysis of Variance; D019540:Area Under Curve; D003627:Data Interpretation, Statistical; D006801:Humans; D015233:Models, Statistical; D015588:Observer Variation; D012372:ROC Curve; D011859:Radiography; D012107:Research Design; D018401:Sample Size