> Figure 3. Difference in low-back surgery (study minus control)

From "Can Evidence Change the Rate of Back Surgery?" Effective Clinical Practice, May/June 2001. 4:261-270.

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Figure 2. Timing of interventions and quarterly rates of low-back surgery. A hinged, least-squares regression was fitted to the study and control group time series to emphasize trends in the actual data. CME = continuing medical education.

Figure 3. Difference in low-back surgery (study minus control). A hinged, least-squares regression was fitted to this difference to test whether the rate of change in mean difference between the study and control communities (i.e., the slope of the difference regression) had significantly changed between baseline and intervention periods.

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