Beck reviewed ten reports of retest reliability of the BDI at varying time intervals; Pearson correlations between administrations ranged from 0.48 to 0.86 in five studies of psychiatric patients and from 0.60 to 0.83 in six nonpsychiatric populations (4, Table 2). Among elderly patients, test-retest reliability at six to 21 days was 0.79 in depressed patients, and 0.86 in nor- mal respondents (17, Table 1). A seven-week retest correlation was 0.79 for undergraduate students (18, p480). Pearson retest correlations may, of course, mask systematic changes in the distribution of scores over time, and there is some evidence that BDI scores may decline by about three points over a period of a month in the absence of any form of intervention (19, Fig- ure 1).