Identification of pain categories associated with change in pain in patients receiving placebo: data from two phase 3 randomized clinical trials in symptomatic knee osteoarthritis

Table 2 Estimated Regression-to-the-mean

WOMAC sub-score	SD	σ²_b	σ²_w	Estimated RTM effect from BL to Y2 (%)	Pain change from BL to Y2 adjusted for estimated RTM effect (%)
Question 1: Walking on flat surface	56	1602.5	1533.5	32.6	0.9
Question 2: On stairs	38	735.0	709.0	26.0	−10.9
Question 3: Lying in bed	80	3872.0	2528.0	33.7	11.2
Question 4: Sitting or lying	69	2551.9	2209.1	35.6	6.3
Question 5: Standing	57	1614.8	1634.3	33.9	−0.1
Questions 1, 2, and 5: Weight-bearing	39	734.6	786.4	27.8	−15,4
Questions 3 and 4: Non-weight-bearing	65	2433.6	1791.4	31.2	−4.6

The percentage of RTM of the Target knee as estimated using the method of Barnett et al. [24]. Calculation of σ²_w was based on within patient data from screening visit and subsequent baseline visit, between 1 and 3 weeks apart. σ²_b: Between patient-variance. σ²_w: Within patient-variance. BL Baseline. Y2 Year 2, RTM Regression to the mean

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