Brief geriatric depression scale as a measure of change in level of depression

Self-report depression scales are often used as outcome measures in clinical trials for depression, one of which is the Geriatric Depression Scale (GDS; (Cheng et al., 2012; Fields et al., 2012). At the same time, much research has shown that brief versions of depression instruments, including the GDS, are as effective as full or longer versions in identifying clinically significant depression. What is not clear is whether brief depression scales are also suitable for assessing changes in depression level, so that they may be used as outcome measures in clinical trials as well. Shorter measures may be more practical for trials conducted in primary care and community settings where the administration of longer instruments may be a challenge. One such GDS scale is a four-item version (GDS-4) developed from the original 30-item version (GDS-30). Its utility and validity have been established in a series of studies. It correlated at r> 0.80 with GDS-30 and the more commonly used 15-item version (GDS-15), and was able to classify depressive cases as well as the two longer versions (Cheng and Chan, 2004; Cheng and Chan, 2005; Cheng et al., 2010). Because it has only a five-point spread (i.e., 0–4), it is interesting to find out to what extent it responds to changes in depression relative to the longer versions. In a study by Cheng and colleagues (Cheng et al., 2010), 150 outpatients received psychiatric evaluation and responded to GDS-15 and GDS-4. The thresholds for the two versions were 8 and 2, respectively. One hundred and ten of these patients were re-evaluated 6months later as they returned for follow-up; the rest dropped out of treatment or did not require follow-up. There were no significant differences between those with follow-up and those without age, gender, and baseline depression scores. Among the 110 patients with follow-up, 71 were depressed at baseline, of which 64 were assessed to have improved (i.e., not clinically depressed) by the treating clinician. These 64 improved cases became the sample of this analysis. For them, the GDS-15 decreased by 4.36 points, corresponding to a Cohen’s d= 1.02, whereas the GDS-4 decreased by 1.27 points (d=0.85). The two change scores correlated at r=0.80, suggesting that change on the GDS-4 corresponded well with change on the GDS-15. However, a larger sample would be needed to obtain the same statistical power for the GDS-4 due to the larger standard deviation value, and hence standard error, when compared with that of the GDS-15. One of the reasons was due to the floor effect when measuring change on the GDS-4; 60% of those improved had their scores dropped to zero, compared with 23% for the GDS-15. Thus, as expected, the GDS-15 offers a finer metric of change, but the GDS-4 is also a viable alternative. Changes on the two measures correspond rather well. The floor effect in GDS-4 may compromise somewhat its utility as an outcome measure, but the degree of this limitation appears to be quite acceptable for such a short measure. We suggest that brief measures, such as the GDS-4, may be best treated as optional outcome measures in pilot trials for which the primary aim is to gain preliminary data rather than definitive conclusion, thus saving resources for the main trial.