The design of a valid and reliable questionnaire to measure osteoporosis knowledge in women: the Osteoporosis Knowledge Assessment Tool (OKAT)

BACKGROUND Osteoporosis knowledge is an important contributor to improving exercise and calcium intake behaviour. However, there are few validated instruments for measuring osteoporosis knowledge levels. The aim of this study was to design a valid and reliable instrument to measure osteoporosis knowledge in Australian women. METHODS A 20 item instrument with true, false and don't know responses was drafted, based on the Osteoporosis Australia Osteoporosis Prevention and Self-management course and the information leaflet "Understanding Osteoporosis". The scoring range was 1 to 20. This was administered to a 467 randomly-selected, healthy women aged 25-44 years. Questionnaire performance was assessed by Flesch reading ease, index of difficulty, Ferguson's sigma, inter-item and item-total correlations, Cronbach's alpha and principal component factor analysis. RESULTS Flesch reading ease was higher than desirable at 45, but this was due to the use of the word osteoporosis in many items. Of the individual items 17 had an index of difficulty less than 0.75. The questionnaire had a Ferguson's sigma of 0.96, a Cronbach's alpha of 0.70 and factor analysis consistent with only one factor (osteoporosis knowledge) being measured. Levels of osteoporosis knowledge were low with a mean score of 8.8 out of 20 which suggests the OKAT may be sensitive to change. CONCLUSIONS The OKAT for measuring osteoporosis knowledge has good psychometric properties in Australian 25-44 year old females. While it should be applicable to other Caucasian populations, this will require confirmation by further research.