Assessing regression to the mean effects in health care initiatives

Table 2 Regression to the mean effects for Physical Component Summary (PCS) scores on the Short Form-12 (SF-12v2), from the high-risk (PCS values ≤ 44.25) subgroup of controls ( n = 34) participating in a health coaching study (Butterworth et al. 2006)

Variable	Mean	Std. error	[95% Confidence Interval]
Actual
Pre-test	36.65	2.21	32.32	40.97
Post-test	44.93	3.27	38.51	51.34
RTM	8.28	2.01	4.35	12.21
Calculated
Pre-test	40.02	0.78	38.49	41.56
Post-test	43.41	1.52	40.44	46.38
RTM	3.38	0.94	1.54	5.22
Difference (Actual – Calculated)
Pre-test	−3.38	0.83	−5.01	−1.74
Post-test	1.52	1.82	−2.04	5.09
RTM	4.90	1.93	1.12	8.68

Notes: “Actual” indicates that the pre-test, post-test and RTM effects were estimated directly from the data. “Calculated” indicates that Equations 1, 5 and 6 were applied directly to the existing data. Standard errors and 95% confidence intervals were derived by bootstrap resampling of the data 1000 times.

ISSN: 1471-2288