How many repeated measures in repeated measures designs? Statistical issues for comparative trials

Table 1 Empirical estimates of correlations from a variety of studies

Endpoint	When assessed	Pre*	Post**	Mix***
Profile of Mood States[10]	Immediately before and after a single treatment			0.83
Profile of Mood States[10]	Every three days during hospitalization		0.56	0.54
Cancer pain⁺	2, 24 and 48 hrs after single treatment		0.67
Daily scores of migraine headache⁺	Four weeks at baseline and at one year later	0.53	0.59	0.48
Brief Fatigue Inventory⁺	Weeks -1, 0, 5 and 6	0.76	0.94	0.65
Hot flashes⁺	Daily for one week at baseline and six weeks later	0.40	0.8	0.54
Shortness of breath⁺	Daily for seven days		0.82
Muscle soreness after running [11]	Twice daily for five days		0.58
Chronic neck pain [12]	Baseline and three weeks later			0.39
Neck range of motion [13]	Before and after a single treatment			0.88
Neck pain [13]	Before and after a single treatment			0.9
Constant Murley score of shoulder pain and dysfunction [14]	Baseline and four weeks later			0.57
Back pain by visual analog score [6]	Baseline and four weeks later			0.56
In chronic headache patients⁺:
SF36 Physical functioning	Baseline and one year later			0.75
SF36 Role limitation physical	Baseline and one year later			0.47
SF36 Role limitation emotional	Baseline and one year later			0.36
SF36 social functioning	Baseline and one year later			0.45
SF36 bodily pain	Baseline and one year later			0.52
SF36 general health	Baseline and one year later			0.74
SF36 health change	Baseline and one year later			0.24
SF36 energy fatigue	Baseline and one year later			0.66
Tumor size in mice [15]	Every three days			0.89
Prostate specific antigen [16]	Four times over 8 to 16 months		0.58

⁺ unpublished data * Mean correlation between baseline measures **Mean correlation between follow-up measures *** Mean correlation between baseline and follow-up measures

ISSN: 1471-2288