The influence of the administration method on scores of the 15-item Geriatric Depression Scale in old age

Abstract

Many rating scales can be self-administered or interviewer-administered, and the influence of administration method on scores is unclear. We aimed to study this influence on scores of the Geriatric Depression Scale (GDS-15), used as a screening instrument in general practice. In two general practices 376 registered patients aged 75years and older were asked to participate. Exclusion criteria were dementia and current treatment for depression. GDS-15 was administered twice within 1month: self-administered by mail, and interviewer-administered during home visits. The sequence of administering the methods was different for the two practices. We analyzed differences in total and item GDS-scores. Of 141 subjects that participated (response rate 55%) 59 were men (42%). Mean age was 81.4years (SD 4.8). When GDS-15 was self-administered, 33 subjects (23.4%) left items unanswered. There were no items unanswered when GDS-15 was interviewer-administered. On average the self-administered total GDS-scores were 0.70 points higher than interviewer-administered scores (CI95%=0.41; 0.98), with a large range of variation in the scores (limits of agreement -2.69 to 4.08). Item-item comparisons showed high percentages of agreement. Chance-corrected agreement (kappa) was moderate to fair, but three items showed only slight agreement (kappa values <0.21). In conclusion, compared to interviewer-administered scores, scores on self-administered GDS-15 were higher. The method of administration should be taken into account when interpreting scores.