Can we convert between outcome measures of disability for chronic low back pain?

STUDY DESIGN

Retrospective database analysis.

OBJECTIVE

A range of patient-reported outcomes were used to measure disability due to low back pain. There is not a single back pain disability measurement commonly used in all randomized controlled trials. We report here our assessment as to whether different disability measures are sufficiently comparable to allow data pooling across trials.

SUMMARY OF BACKGROUND DATA

We used individual patient data from a repository of data from back pain trials of therapist-delivered interventions.

METHODS

We used data from 11 trials (n=6089 patients) that had at least 2 of the following 7 measurements: Roland-Morris Disability Questionnaire, Chronic Pain Grade disability score, Physical Component Summary of the 12- or 36-Item Short Form Health Survey, Patient Specific Functional Scale, Pain Disability Index, Oswestry Disability Index, and Hannover Functional Ability Questionnaire. Within each trial, the change score between baseline and short-term follow-up was computed for each outcome and this was used to calculate the correlation between the change scores and the Cohen's κ for the 3-level outcome of change score of less than, equal to, and more than zero. It was considered feasible to pool 2 measures if they were at least moderately correlated (correlation>0.5) and have at least moderately similar responsiveness (κ>0.4).

RESULTS

Although all pairs of measures were found to be positively correlated, most correlations were less than 0.5, with only 1 pair of outcomes in 1 trial having a correlation of more than 0.6. All κ statistics were less than 0.4 so that in no cases were the criteria for acceptability of pooling measures satisfied.

CONCLUSION

The lack of agreement between different outcome measures means that pooling of data on these different disability measurements in a meta-analysis is not recommended.

LEVEL OF EVIDENCE