Developing a questionnaire to measure patients' beliefs about inhaler treatment for asthma: Tests of validity and reliability.

Aim: To develop a valid and reliable questionnaire for measuring patients' beliefs about inhaler treatments for asthma.

Methods: In seven general practices, 335 patients prescribed both beclomethasone and salbutamol inhalers completed a 66-item questionnaire. Sub-scales were developed using factor analysis and a 29-item questionnaire sent to 90 patients in another practice to estimate test-retest reliability.