Evaluating minimal clinically important differences for the acne-specific quality of life questionnaire

Background: The Acne-Specific Quality of Life Questionnaire (Acne-QoL) is a responsive, reliable and valid instrument developed to measure the impact of facial acne across four dimensions of patient QOL. Score changes on this instrument have been used to report statistically significant treatment advantages for a low-dose oral contraceptive (Estrostep(R)), containing norethisterone (norethindrone) acetate (NA) 1mg and ethinylestradiol (EE) [20, 30, 35mg] as compared with placebo in women with moderate acne vulgaris. However, the question remained if these statistically significant results were also clinically meaningful. Objectives: To evaluate the statistically significant Acne-QoL benefits observed with NA/EE in terms of their clinical significance, and to compare the three different approaches for defining a minimal clinically important difference (MCID) for the Acne-QoL instrument. Methods: Since the optimum method for estimating MCIDs has yet to be established, three different published approaches for determining MCIDs were applied and compared using data from two randomised, double-blind, placebo-controlled studies of the efficacy of NA/EE in the treatment of facial acne. Results: Although the approaches differed substantially, the resulting MCID estimates were comparable. Specifically, the MCID estimates ranged from 0.50-10.3 mean change per item, depending on the domain. The results showed that the statistically significant treatment advantages for NA/EE were also clinically significant. Conclusion: When applied to the change scores present, the results showed that the statistically significant treatment advantages for NA/EE were also clinically significant.