Observer variation in assessing renal scarring.

To examine the extent of variation between experienced observers in recognizing renal scarring, 60 intravenous urograms from schoolgirls with bacteriuria were presented separately to three radiologists with a major interest in the radiology of the urinary tract. Observers were asked to state whether scarring was "absent", "doubtful" or "present" at each of three sites in each kidney: the poles and the midportion. The proportion of overall agreement, i.e. the proportion of coincident opinions, was 86% to 89%. Results were also analysed by using the kappa statistic, which corrects for agreement due to chance. Kappa values ranged from 0.67 to 0.73. These values indicate higher levels of inter-observer agreement than those recorded for many other radiological examinations and are much greater than those noted by others for inter-observer variation in the recognition of renal scarring in urograms in adults. The likely explanations for these high levels of agreement are discussed. Observers disagreed about the extent of scarring in one-third of cases. Studies of the prevalence of scarring should take account of observer variation and should be based on judgments by more than one experienced observer.