Accuracy of telephone self-report of drug use in older people and agreement with pharmaceutical claims data.

Objective: To determine the agreement between two measures of medication use, namely telephone interview self-report and pharmaceutical claims data, in an elderly population.

Methods: An agreement study of 566 community-dwelling, general practice patients aged > or =65 years was conducted to compare self-reported use of medicines with pharmaceutical claims data for different retrieval periods. Classes of drugs commonly used in the elderly were selected for comparison.

Results: 1094 people were eligible for the main study. Of these, 697 people completed a follow-up survey and 625 of these patients consented to the release of pharmaceutical claims data. A further 59 participants were excluded from the analysis because they had a home visit instead of a telephone interview. The proportion of observed agreement between the telephone self-report and the various retrieval periods was consistently high. Kappa coefficients showed good to very good agreement (> or = 0.75) with retrieval periods of 30, 60 and 90 days for benzodiazepines, low-risk NSAIDs, thiazide diuretics and most other drugs. The specificity of self-reported medication use compared with claims data was consistently high across all drug classes, suggesting that people usually did not mention drugs that were not included in the claims data. Sensitivity values varied according to drug class and retrieval period, and were lower for NSAIDs than for benzodiazepines and thiazide diuretics. Decline in sensitivity with increased retrieval periods was most marked for benzodiazepines, NSAIDs and low-risk NSAIDs, which are often used on an as-needed basis. Positive predictive values increased with longer retrieval periods

Conclusion: High agreement and accuracy were demonstrated for self-reported use of medicines when patients were interviewed over the telephone compared with pharmaceutical claims data. The telephone inventory method can be used in future studies for accurately measuring drug use in older people when claims data are not available.