Study design: An intrapatient reliability study of the previously validated 18-item questionnaire, the Balanced Inventory for Spinal disorders (BIS), in patients referred for planned spinal surgery. Statistical evaluation of the test-retest assessments was performed by a rank-based method that allows for separate analyses of the systematic and individual components of an observed disagreement.
Objective: To evaluate the intrapatient reliability and the art of disagreement, when present, in assessing the extent to which pain affects perceived physical health, social life, mental health, and quality of life according to the BIS. For comparative reasons corresponding items in Short-Form-36 (SF-36) and Oswestry Disability Index (ODI) were also evaluated.
Summary of background data: The questionnaires were filled in by 101 patients the evening before going to the clinic for planned spinal surgery and the following evening at the clinic.
Results: The percentage agreement in test-retest assessments of the items varied from 52% to 84%. The important items of pain, physical activities, social life, overall mental health, and quality of life showed high levels of reliability. An intrapatient disagreement of more than 1 category was seen in 4 items of mental health and in physical health, only. The observed individual variability and the significant systematic decrease on the second occasion could be explained by the fact that the patients were at the hospital on the retest occasion. The variation in percentage agreements found, and the different reasons for disagreement in items speak against that memory alone could have caused the retest assessments.
Conclusion: The comprehensive evaluation of test-retest reliability showed that the test-retest assessments on the BIS could be regarded as reliable, and the measures of reliability of the BIS items were on the same levels as for corresponding items of the SF-36 and the ODI questionnaires.