Table 2

Physical function instruments, metric scores, and sample size requirements

Standardized response mean

Cohen's effect size

Guyatt's effect size

Minimum detectable difference

Sample size requirement n (95% CL1)


Legacy PF-10

0.10

0.06

0.49

2.43

427 (345, 514)

Legacy HAQ

0.14

0.06

0.52

1.40

143 (113, 176)

Item-Improved PF-10

0.09

0.05

0.59

2.16

336 (245, 436)

Item-Improved HAQ

0.13

0.05

0.73

1.14

95 (76, 117)

PROMIS PF 10

0.13

0.05

0.52

1.47

157 (127, 189)

PROMIS PF 20

0.13

0.05

0.63

1.24

113 (90, 141)


1 Confidence Limits

HAQ, health assessment questionnaire; Item-Improved, Changes to items intended to improve their performance by altering parameters such as time frame and response options while retaining the same item stem; PF, physical function; PROMIS, Patient-Reported Outcomes Measurement Information System.

Fries et al. Arthritis Research & Therapy 2011 13:R147   doi:10.1186/ar3461

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