Randomised controlled comparison of the Health Survey Short Form (SF-12) and the Graded Chronic Pain Scale (GCPS) in telephone interviews versus self-administered questionnaires. Are the results equivalent?

Table 3 Condition-based mean values (M) and standard deviation (SD) for GCPS: pain intensity (PI) and pain-related disability (PD) scales

		Telephone interview		Self-administered questionnaire
Timing of information about second survey	Survey-mode sequence	PI M (SD)	PD M (SD)	PI M (SD)	PD M (SD)	N
Delayed	Self-administered questionnaire first	55.56 (19.3)	31.20 (25.7)	55.56 (19.8)	34.53 (26.7)	205
	Telephone interview first	52.32 (19.9)	26.75 (25.4)	52.68 (19.7)	30.96 (24.7)	194
	Total	53.99 (19.7)	29.03 (25.7)	54.16 (19.8)	32.79 (25.7)	399
At outset	Self-administered questionnaire first	56.39 (17.8)	31.06 (24.9)	55.34 (20.4)	34.55 (25.7)	203
	Telephone interview first	56.00 (20.9)	30.75 (26.2)	55.68 (20.2)	32.37 (24.3)	190
	Total	56.20 (19.3)	30.91 (25.5)	55.50 (20.3)	33.51 (25.0)	393
Total	Self-administered questionnaire first	55.97 (18.6)	31.13 (25.3)	55.45 (20.1)	34.54 (26.2)	408
	Telephone interview first	54.14 (20.5)	28.71 (25.8)	54.17 (20.0)	31.65 (24.5)	384
	Total	55.08 (19.5)	29.96 (25.6)	54.83 (20.0)	33.15 (25.4)	792