Development and validation of the Curtin Bach Screening Questionnaire (CBSQ): a discriminative disability measure

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Abstract
Disability accompanying occupational low back pain (LBP) can include a wide range of incapacitating symptoms which, for the practitioner, can be time-consuming and difficult to identify systematically. A questionnaire designed for case-finding and assessment could assist in both the early recognition of disability and in planning management. A suitable questionnaire for clinical use could not be found in the literature. The Curtin Back Screening Questionnaire (CBSQ) was developed, therefore, as a discriminative screening instrument to serve this purpose. The methods and results of the development and validation of the CBSQ are presented herein. Development of the questionnaire followed the principles of Kirschner and Guyatt (1985) employing data from 74 subjects with at least moderately severe work-related LBP. The research design for the validation was multiple-group repeated-measures with a study population of 150 subjects. The screening function of the questionnaire was developed through selecting 8 questions from the whole questionnaire using regression analysis. The questionnaire includes 79 items based on the subjects' perceived health status. The response structure of the CBSQ has been adapted from that of the General Health Questionnaire (GHQ) and some items in the CBSQ have been developed from items in the Sickness Impact Profile (SIP) and GHQ. The questionnaire discriminates effectively between subjects with different degrees of disability, it correlates quite well with the SIP, test-retest reliability for the whole questionnaire is 0.98, the receiver-operating characteristics are more favourable than those for the SIP, and the CBSQ screening score provides an index of severity which correlates with work incapacity. The CBSQ is a self-administered discriminative instrument designed specifically for subjects with disabling occupational LBP. It can be used clinically and in surveys by providing a disability severity score for screening purposes, as well as an itemised description of disability within 11 categories of functional incapacity.