Comparative reliability of categorical and analogue rating scales in the assessment of psychiatric symptomatology.

The reliability of 26 items from the ninth edition of the Present State Examination (PSE) was assessed using both the conventional categorical scales and separately constructed analogue scales. Reliability was also calculated when the analogue responses were rescaled down to 2, 3 and 4 categories. The levels of inter-rater agreement obtained were comparable to those achieved in previous studies of PSE reliability, although as expected the levels of agreement on audiotapes were greater than those for independent interviews performed on the same day. These levels were not significantly affected by any of the changes in scale format, but there were apparent differences in reliability depending on the statistics used. In selecting or constructing a psychiatric rating scale, the question of reliability should not influence the choice of a categorical or continuous scale, or the number of scored points in the scale.