Development and validation of an audit instrument: the Prostate Outcomes Questionnaire

D L Lamping, P Rowe, N Black, L Lessof
British Journal of Urology 1998, 82 (1): 49-62

OBJECTIVE: To develop a short, patient-based questionnaire for auditing the outcomes of treatment for benign prostatic hyperplasia (BPH) and to evaluate the acceptability, reliability and validity of the measure.

PATIENTS AND METHODS: Data from a long research questionnaire used in the Oxford/North West Thames Prostatectomy Study were analysed to identify the subset of items which contained the most scientifically sound indicators of outcome. Items were selected on the basis of standard psychometric analyses to develop a short questionnaire, the Prostate Outcomes Questionnaire (POQ), a 27-item instrument covering urinary symptoms, complications after surgery, quality of life and patient satisfaction with outcome. The POQ was field tested for acceptability, reliability and validity in a postal survey of 125 men undergoing transurethral resection of the prostate for BPH from seven hospitals in south-east England.

RESULTS: The POQ was highly acceptable to patients, as indicated by a 95% response rate, the absence of 'floor' and 'ceiling' effects and a low proportion of missing data. It showed excellent internal consistency reliability (Cronbach's alpha of 0.82-0.93 for the five summary scales and a mean item-total correlation of 0.56) and test-retest reliability (test-retest correlations for items were 0.40-1.00, with a mean test-retest correlation of 0.85, and for summary scales of 0.91-0.95). Construct validity was confirmed by: high intercorrelations between the five summary scales and the total score (0.88-0.95), with a pattern of intercorrelations among specific subscales that showed item-convergent and discriminant validity; higher scores for patients who reported an improvement after surgery than in those who were not improved (P < 0.001); the expected gradient of scores for patients reporting different levels of symptom distress (P < 0.001); high correlations with the longer parent questionnaire (0.75-0.88); and low to moderate correlations with the Nottingham Health Profile and Activities of Daily Living scores (0.15-0.67), with the pattern of correlations providing evidence of scale convergent and discriminant validity. Correlations with age and social class were low, suggesting that responses were not biased by sociodemographic factors.

CONCLUSION: The POQ is a practical and scientifically sound patient-based measure of outcome after treatment for BPH which can be used for routine audit. It takes < 5 min to complete, is feasible for routine monitoring of large numbers of patients by postal survey, and is accompanied by a Users' Manual which provides practical help in conducting a local patient survey, and a computer program for scoring data. Most importantly, the POQ has been shown scientifically to perform well, having met standard psychometric criteria for reliability and validity.

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