Validation of the General Practitioner Clinical Research Group 11-item depression scale

In trials performed by the General Practitioner Clinical Research Group two rating scales have been employed extensively to measure depression. One includes some 17 target symptoms whilst the second is a shorter scale of 11 items. Although extensively used, neither scale has been validated against other measures of depression. An attempt was made to validate the 11-item scale, completed by the physician, against the Zung self-rating depression scale and the Wakefield Inventory, both patient-completed scales. Using thirty depressed patients the correlation between the 11-item scale and the Zung was 0.59 and between the 11-item scale and the Wakefield it was 0.5. Surprisingly, although the two scales are patient-completed and purport to measure the same thing, the correlation between the Zung and the Wakefield scales was only 0.69. All the correlations were statistically significant at the 1% level.