Measuring quality of life in cosmetic surgery patients with a condition-specific instrument: the Derriford Scale
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OBJECTIVE: To assess the reliability, validity and sensitivity to change of the Derriford Scale, a quality of life instrument designed to assess the distress and dysfunction experienced by people who are self-conscious about their physical appearance. SUBJECTS AND DESIGN: Postal questionnaire survey of 656 cosmetic surgery patients recruited from new referral letters and plastic surgery waiting list reports. A total of 443 subjects completed and returned the questionnaire. Of these respondents, 203 were sent a second questionnaire to assess reproducibility, of whom 155 subjects responded. MAIN OUTCOME MEASURES: Reliability was assessed in terms of internal consistency and reproducibility. Face, content and construct validity were also investigated. RESULTS: The analyses led to mixed results. There was some evidence of internal consistency, but a number of items had low endorsement levels and there may be scope for reducing the overall size of the instrument. When assessed for reproducibility, the level of agreement between scores of individuals completing the questionnaire on two occasions was high, but an important systematic shift in responses was also detected. Correlations between the other health status measures and the Derriford Scale provided some evidence of construct validity. CONCLUSION: In its present form the Derriford Scale has good descriptive value, but there are some measurement problems identified in this report that need to be addressed before the scale is taken up into general use.
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