Interobserver and intraobserver differences in the diagnosis of urothelial cells. Comparison with classification by computer.

The diagnostic performance of six human observers with various degrees of experience was tested against the diagnosis developed by consensus and by an automated, computer-generated cell-classification system. The study was based on randomly selected photographs of 200 urothelial cells, classified in groups of 50 as negative, atypical, suspicious and malignant, from smears of urine sediment. The performance of the human observers was tested in three separate sessions at suitable time intervals and evaluated by two analytical statistical techniques: the weighted kappa proposed by Cohen, to evaluate the degree of disagreement, and the log-linear analysis of association. The results indicated considerable interobserver and intraobserver differences, which appeared to be more closely related to the individual's perception of the visual targets than to the degree of experience or the target itself. The performance of the programmed computer was well within the midrange of the human diagnostic performance. This study indicated that under the experimental circumstances described in this paper, the diagnostic perception of cell images is highly subjective. The study implies that similar differences may exist elsewhere in diagnostic microscopy and suggests that the development of objective approaches to the morphologic classification of human disease may prove to be of clinical value.