title: Prevalence effect in a laboratory environment.
abstract: OBJECTIVE
  To measure observer performance at various levels of prevalence.
  
  
  METHODS
  A multiobserver multiabnormality receiver operating characteristic (ROC) study to assess the effect of prevalence on observer performance was conducted. Fourteen observers, including eight faculty members, two fellows, and four residents, interpreted 1,632 posteroanterior chest images with five prevalence levels by using a nested study design. Performance comparisons were accomplished by using a multireader multicase approach to assess the effect of prevalence from 28% (69 of 249) to 2% (31 of 1,577) on diagnostic accuracy. The mean times required to review and report a case were analyzed and compared for different levels of prevalence and readers' experience.
  
  
  RESULTS
  Area under the ROC curve demonstrated that, with the study experimental conditions, no significant effect could be measured as a function of prevalence (P >.05) for any abnormality, group of cases, or readers. There were no significant differences (P >.05) in the mean times required to review and report cases at different prevalence levels and with different groups of readers.
  
  
  CONCLUSIONS
  The consistency in the results and the size of this study suggest that with laboratory conditions, if a prevalence effect exists, it is quite small in magnitude; hence, it will not likely alter conclusions derived from such studies.
authors.affiliation: Department of Radiology, Imaging Research, Suite 4200, University of Pittsburgh, 300 Halket St, Pittsburgh, PA 15213-3180, USA. gurd@msx.upmc.edu
authors.forename: David
authors.initials: D
authors.lastname: Gur
authors.forename: Howard E
authors.initials: HE
authors.lastname: Rockette
authors.forename: Derek R
authors.initials: DR
authors.lastname: Armfield
authors.forename: Arye
authors.initials: A
authors.lastname: Blachar
authors.forename: Jennifer K
authors.initials: JK
authors.lastname: Bogan
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Brancatelli
authors.forename: Cynthia A
authors.initials: CA
authors.lastname: Britton
authors.forename: Manuel L
authors.initials: ML
authors.lastname: Brown
authors.forename: Peter L
authors.initials: PL
authors.lastname: Davis
authors.forename: James V
authors.initials: JV
authors.lastname: Ferris
authors.forename: Carl R
authors.initials: CR
authors.lastname: Fuhrman
authors.forename: Sara K
authors.initials: SK
authors.lastname: Golla
authors.forename: Sanj
authors.initials: S
authors.lastname: Katyal
authors.forename: Joan M
authors.initials: JM
authors.lastname: Lacomis
authors.forename: Barry M
authors.initials: BM
authors.lastname: McCook
authors.forename: F Leland
authors.initials: FL
authors.lastname: Thaete
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Warfel
mesh_terms: D007753:Laboratories; D015588:Observer Variation; D015995:Prevalence; D012372:ROC Curve; D013902:Radiography, Thoracic