The middling tendency in reading chest films for pneumoconiosis: an important source of bias and variability.

The tendency for readers of chest films of the pneumoconioses to place films in the middle of the International Labour Office (ILO) categories of profusion (eg, 1/1, 2/2) was described by Morgan et al [1974], who saw this tendency as a possible source of bias. The present study reexamines the middling tendency in relation to bias and variability by comparing duplicate readings of chest films for pneumoconiosis. Readings of trained lay persons were compared to professional readings of the same films and readings of professional readers were compared with each other. Reasons for the middling tendency, which include the use of standard middle films and the instructions given to users of the classification, are suggested and possible solutions are proposed.