Table 8 Estimates from segmented linear regression for adverse events in Site 1

 Intercept

3.08 (2.93, 3.24)

< 0.00001

 Pre-intervention trend

0.02 (0.00, 0.03)

0.04

Adverse events were very gradually but significantly increasing during this period. Given the low overall rates the clinical impact of this increase is difficult to determine.

 Change in slope (implementation period vs. pre-intervention period)

0.03 (−0.03, 0.09)

0.29

There was a trend towards an increasing rate of adverse events (against the expected trend) but this was not significant. The wide confidence intervals mean the trend could have been in either direction should a greater sample size have been available.

 Immediate change in level (implementation period vs. pre-intervention period)

0.15 (− 0.34, 0.64)

0.55

 Change in slope (post-intervention period vs. implementation period)

-0.09 (−0.15, − 0.05)

< 0.001

Adverse event rates decreased by nearly 10% in this period, compared to the implementation period, which was statistically significant.

 Immediate change in level (post-intervention period vs. implementation period)

−0.43 (−1.03, 0.17)

0.16