Objective: The aim of this study was to evaluate the comparability of ACT * scores from a telephone interview format ('Telephone') against the original paper-and-pencil format ('Paper'). * Asthma Control Test (ACT) is a registered trademark of QualityMetric Incorporated, Lincoln, RI, USA METHODS: This was a randomized, crossover design with subjects completing both paper and telephone interview questionnaires. Subjects were >or=18 years old, with an asthma diagnosis, and receiving treatment within the last year. Eligible subjects were randomized to one of four administration form (AF) groups--(1) Telephone-Telephone, (2) Paper-Paper, (3) Paper-Telephone, (4) Telephone-Paper. Internal consistency and test-retest reliability were compared across groups. Differential item functioning (DIF) tests were conducted at baseline to evaluate AF effects on individual ACT items. Unadjusted and adjusted mean ACT scores were compared between AFs at baseline and unadjusted and adjusted means changes in ACT scores from baseline to follow-up were compared across the four groups. Lastly, the ability of ACT scores to discriminate between self-reported asthma severity was compared between the AFs using ANOVA.
Results: A total of 1090 asthma respondents completed paper (n = 579) and telephone interview (n = 511) questionnaires. Internal consistency reliability of ACT scores at baseline was 0.81 and 0.83 for the paper and telephone AFs, respectively. Test-retest reliabilities ranged from 0.87 to 0.91 across the four groups. Responses to ACT items showed no significant DIF between AFs (chi(2) = 6.6, p = 0.25). ACT scores differed significantly across asthma severity levels in the hypothesized way for both paper (F = 230.1, p < 0.001) and telephone (F = 173.4, p < 0.001) AFs.
Conclusion: ACT scores from a telephone interview are reliable and comparable to ACT scores from a self-administered paper-and-pencil format. A potential limitation concerns the representativeness of study participants of asthmatics in the population.