The validity and reliability of an asthma knowledge questionnaire used in the evaluation of a group asthma education self-management program for adults with asthma

This paper reports aspects of the validity and reliability of an asthma general knowledge questionnaire for adults (AGKQA), developed as one of the outcome measures for a randomized controlled effectiveness trial of an asthma education program for adults with asthma. It also illustrates how study data can provide a valuable, generally neglected opportunity to assess the validity and reliability of a measure where resources are not available for the extensive investigation of these properties prior to administration of the measure in a study. The AGKQA was demonstrated to have good content and face validity. Construct validity assessed using the principal components method for factor analysis suggested the scale was unidimensional. Criterion-related validity, assessed using the contrasted groups method, demonstrated a significant difference (p < 0.0001) in total score and for 68% of item responses for the adults with and without direct experience of asthma. The Kuder-Richardson 20 reliability coefficient for internal consistency calculated using responses at baseline, immediately, and 12 months post-intervention were, respectively, 0.56, 0.80, and 0.75, indicating excellent reliability. The AGKQA is an acceptably valid and reliable measure for the assessment of program content mastery that it was designed to test.