Validation of a measure of knowledge about human papillomavirus (HPV) using item response theory and classical test theory.

OBJECTIVE: Public understanding of HPV is important to ensure informed participation in cervical cancer prevention programmes. While many studies have measured HPV knowledge, none has developed a validated measure for use across countries. We aimed to develop and validate such a measure. METHOD: Items tapping knowledge of HPV, HPV testing and HPV vaccination were developed from previous literature and with expert consultation. The 29-item measure was administered via the internet to 2409 adults in the UK, US and Australia in 2011. Classical test theory and item response theory were used to establish the measure's psychometric properties. RESULTS: Total scale reliability was very good (α = 0.838), as was internal consistency for a 16-item general HPV knowledge subset (α = 0.849). Subsets of HPV testing and vaccination items showed reasonable test-retest reliability (r(test-retest) = 0.62 and 0.69) but moderate internal consistency (α = 0.52 and 0.56). Dimensionality analyses suggested that one item was not measuring the same construct as the remainder of the questionnaire. A 2-parameter logistic item response theory (IRT) model was fitted to the remaining 28 scale items. CONCLUSIONS: A structurally coherent set of items covering a range of important HPV knowledge was developed. Responses indicated a reliable questionnaire, which allowed the fitting of an IRT model.