Sample size estimation for randomised controlled trials with repeated assessment of patient-reported outcomes: what correlation between baseline and follow-up outcomes should we assume?

Table 4 Baseline to post-randomisation follow-up correlations by post-randomisation follow-up time point

Post-randomisation follow-up time point (months)	Pearson baseline to post-randomisation follow-up correlation
Post-randomisation follow-up time point (months)	Mean	Median	SD	Minimum	Maximum	No. of correlations
0.25	0.48	0.48	0.44	0.17	0.79	2
1	0.37	0.39	0.28	0.09	0.64	3
1.5	0.49	0.45	0.12	0.33	0.70	14
2	0.55	0.56	0.12	0.26	0.82	34
3	0.48	0.50	0.15	−0.13	0.72	71
4	0.48	0.49	0.09	0.35	0.63	9
4.5	0.48	0.52	0.09	0.32	0.58	9
6	0.54	0.55	0.16	0.04	0.88	121
8	0.43	0.44	0.13	0.21	0.58	9
9	0.62	0.62	0.16	0.38	0.91	16
10	0.45	0.43	0.08	0.34	0.58	9
10.5	0.42	0.47	0.12	0.19	0.54	9
12	0.46	0.48	0.14	0.01	0.72	86
16.5	0.41	0.42	0.12	0.23	0.57	8
18	0.47	0.49	0.13	0.16	0.67	27
24	0.51	0.53	0.15	0.17	0.84	37

ISSN: 1745-6215