Psychometric evaluation, using Rasch analysis, of the WHOQOL-BREF in heroin-dependent people undergoing methadone maintenance treatment: further item validation

Table 7 Differential item functioning (DIF) items detected across different groups

Group 1	Group 2	Item #	Item description	DIF contrast^a	SE	t-value	p
Junior high and below	Senior high and above	E9	Eating	0.50	0.23	2.23	0.03
Female	Male	S2	Sexual activity	-0.86	0.42	2.05	0.048
HIV-positive	HIV-negative	Ps3	Think	0.63	0.24	2.64	0.01
HIV-positive	HIV-negative	Ps6	Negative feelings	-0.62	0.24	2.62	0.01
HIV-positive	HIV-negative	S1	Personal relationship	-0.71	0.30	2.37	0.02
HIV-positive	HIV-negative	S2	Sexual activity	0.64	0.29	2.18	0.03
HIV-positive	HIV-negative	E7	Health services	-0.57	0.26	2.20	0.03

^aDIF contrasts were calculated as: logit of Group 1 - logit of Group 2; a positive value indicates that a patient in Group 1 has a higher item score than a patient who has the same QoL level in Group 2, and a negative value indicates that a patient in Group 1 has a lower item score than a patient who has the same QoL level in Group 2.
HIV: Human immunodeficiency virus.
Reversely coded items are in italics.

ISSN: 1477-7525