Psychometric characteristics of the Spanish version of instruments to measure neck pain disability

Table 6 Effect size of NDI, NPQ and COM for patients having worsened, not changed or improved between days 1 and 16, according to external criteria for pain and disability.

Scale	Patients' status according to external criterion for disability	N*	Mean	SD	Effect Size**
NDI	Worsened	29	-4.34	17.98	-0.24
	Unchanged	80	2.46	16.07	0.15
	Improved	111	12.20	18.52	0.66
NPQ	Worsened	29	-2.58	18.13	-0.14
	Unchanged	80	1.02	16.18	0.06
	Improved	111	11.69	17.51	0.67
COM	Worsened	26	0.04	0.89	0.05
	Unchanged	79	0.13	0.70	0.19
	Improved	106	0.63	0.69	0.92
Scale	Patients' status according to external criterion for pain	N*	Mean	SD	Effect Size**
NDI	Worsened	35	-4.05	16.21	-0.25
	Unchanged	82	4.02	17.54	0.13
	Improved	103	12.01	17.96	0.67
NPQ	Worsened	35	-5.17	19.36	-0.27
	Unchanged	82	3.21	17.02	0.19
	Improved	103	11.86	16.57	0.72
COM	Worsened	32	-0.02	0.75	-0.02
	Unchanged	78	0.25	0.66	0.38
	Improved	101	0.60	0.75	0.79

*: Total number of patients participating in the study was 221. Missing patients in these tables are due to missing values in either the questionnaire (NDI, NPQ or COM) or the external criterion for pain or disability
** Absolute values for effect size should be interpreted as follows: values < 0.20 correspond to no change, 0.20–0.49 to a small change, 0.50 to 0.79 to a moderate change and ≥ 0.80 to a great change.^21–23

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