A new measure of quality of life in depression: testing the reliability and construct validity of the QLDS.

Our previous paper described the development of a new quality of life scale for use with people suffering from depression; the Quality of Life in Depression Scale (QLDS). This paper reports on the testing of the scale for reliability and construct validity. Reliability was assessed by giving the questionnaire to the same set of patients on two occasions 2 weeks apart. This test-retest technique yielded a correlation of 0.94, with high internal consistency at both time 1 and time 2. A test of split-half reliability also indicated very high reliability. Construct validity was measured by comparing scores on the QLDS with those on an established scale of well-being from the same group of patients. The results gave a correlation between the two measures of 0.79, giving a satisfactory validity. It is concluded that the QLDS is a reliable and valid measure which is easy to use and acceptable to patients. Further tests of discriminative, concurrent and criterion validity are planned.