Improved responsiveness and reduced sample size requirements of PROMIS physical function scales with item response theory

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.

ISSN: 1478-6362