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

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 75 years and older were asked to participate. Exclusion criteria were dementia and current treatment for depression. The GDS-15 was administered twice within 1 month: 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 who participated (response rate 55%) 59 were men (42%). Mean age was 81.4 years (SD 4.8). When the GDS-15 was self-administered, 33 subjects (23.4%) left items unanswered. There were no items unanswered when the GDS-15 was interviewer-administered. On average the self-administered total GDS scores were 0.70 points higher than interviewer-administered scores (95% confidence interval=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 the GDS-15 when self-administered were higher. The method of administration should be taken into account when interpreting scores.