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

Abstract

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.