Interviewer-administered TLFB vs. self-administered computerized (A-CASI) drug use frequency questions: a comparison in HIV-infected drug users.

backgroundSubstance use can have major consequences among HIV patients. Interviewer- or self-administered modalities are widely used to measure drug use frequency. This often involves Timeline Follow-Back (TLFB) interviewer-administered measures, or self-administered computerized questions assessing similar information via Audio Computer-Assisted Self Interview (A-CASI). Little is known about agreement between these two modalities on drug use frequency in HIV-infected samples.

methodsPrior to randomization into a trial of brief interventions to reduce drug use, 240 HIV patients completed a baseline A-CASI assessment battery that included questions on drug use frequency, followed by an interviewer-administered TLFB. Each measure generated number of days patients used their primary drug in the prior 30 days. Agreement between TLFB and A-CASI modalities on days using primary drug was determined using intraclass correlation coefficients (ICC). Regression analysis tested the association of patient characteristics with discrepancies between TLFB and A-CASI modalities.

resultsOverall agreement was excellent (ICC=.80), with little variation by primary drug, education, race, current drug treatment, binge drinking or years since HIV diagnosis. Gender, ethnicity (Hispanic vs. non-Hispanic) and age predicted differences in days used (p<0.05); the A-CASI modality reflected more days used than TLFB.

conclusionsMeasures of days used primary drug showed high agreement whether assessed by interviewer-administered TLFB or by questions self-administered via the A-CASI modality. Differences by gender, ethnicity and age suggest some caution in using the TLFB, although additional studies are needed. However, findings generally indicate that studies based on one assessment method or the other can be compared with reasonable confidence.