Combination of qualitative and quantitative methods for developing a new Health Related Quality of Life measure for patients with anogenital warts

BACKGROUND: Anogenital warts are the most easily recognized sign of genital Human Papilloma Virus infection. The objective was to develop a short, valid and reliable questionnaire to measure Health Related Quality of Life (HRQL) in patients with anogenital warts. METHODS: First a literature review was performed to identify relevant papers describing the impact of anogenital warts in HRQL; second the main domains were identified by some experts in a focus group, and third in-depth-semi-structured interviews were conducted in patients with anogenital warts to identify the initial set of items. A qualitative reduction of the initial set of items was performed based on the mean scoring of the experts for the three scales: clarity, frequency and importance. The initial questionnaire was pilot tested in 135 patients. Rasch analysis was performed with the results of the questionnaire in order to refine the instrument. Spearman's correlation was calculated between the initial questionnaire and the reduced version. Additionally the measurement properties (validity and reliability) of the resulting final questionnaire were tested and compared using standard procedures (Cronbach's Alpha and item-total correlation). RESULTS: the main domains identified as affected in patient's life were: sexual, colleagues and partner relationships. After a proper qualitative reduction the initial set of 134 items was reduced to 22. The questionnaire was pilot tested in 135 patients and two dimensions were identified after the multifactorial analysis: emotional dimension and sexual activity dimension. As a result of the Rasch analysis the questionnaire was reduced to 10 items. High correlation was found between the initial and the reduced version for the two dimensions. Cronbach's alpha values were acceptable (0.86). CONCLUSION: The initial 22 items questionnaire was reduced by Rasch analysis to a version of 10 items, with two dimensions: emotional and sexual. The results suggest the adequacy of the 10 items to evaluate HRQL of patients with anogenital warts in a valid and reliable way.