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.