Interrupted time series analysis
André E. Bussières, DC, MSc, PhD
Abstract
Background Context
Overuse and misuse of spine x–rays for non-specific back and neck pain persists among chiropractors. Distribution of educational materials among physicians results in small to modest improvements in appropriate care such as ordering spine x-rays, but little is known about its impact among North American chiropractors.
Purpose
To evaluate the impact of web-based dissemination of a diagnostic imaging guideline on the use of spine x-rays among chiropractors.
Study Design/Setting: Quasi-experimental design using interrupted time series to evaluate the effect of guidelines dissemination on spine x-ray claims by chiropractors enlisted in managed care network in the US.
Patient Sample
Consecutive adult patients consulting for complaints of spine disorders.
Outcome Measures
A change in level (the mean number of spine x-ray claims per month immediately after the introduction of the guidelines), change in trend (any differences between pre-intervention and post-intervention slopes), estimation of monthly average intervention effect after the intervention.
Methods
The imaging guideline was disseminated online in April 2008. Administrative claims data were extracted between January 2006 and December 2010. Segmented regression analysis with autoregressive error was used to estimate the impact of guideline recommendations on the rate of spine x-rays. Sensitivity analysis considered the effect of two additional quality improvement strategies, a policy change and an education intervention.
Study funding sources
AEB CIHR and KT-Canada PhD Fellowships ($3,000.00), JMG Canada Research Chair ($5,000.00). Study-specific conflicts of interest-associated biases: None declared. No funding was received from the managed care organization.
Results
Time series analysis revealed a significant change in the level of spine x-rays ordering weeks after introduction of the guidelines (-0.01; 95% CI=-0.01,-0.002; p=0.01), but no change in trend of the regression lines. The monthly mean rate of spine x-rays within 5 days of initial visit per new patient exams decreased by 10 per 1000, a 5.26% relative decrease after guideline dissemination. Controlling for two quality improvement strategies did not change the results.
Conclusions
Web-based guideline dissemination was associated with an immediate reduction in spine x-ray claims. Sensitivity analysis suggests our results are robust. This passive strategy is likely cost effective in a chiropractic network setting.
Journal Abstract: http://www.sciencedirect.com/science/article/pii/S152994301301499X