Appendix A1.

Test statistics of the Differential Item Functioning analysis: Step 1

					Gamblers in the general population		Slot machine gamblers
Criterion	Hypothesis Test		G21	d.f.	a	b	a	b	μ	δ
1 Preoccupation	All	equal	19.9	2	0.74	−0.75	1.73	0.49	1.02	0.87
	a	equal	4	1	1.43	−0.52	1.43	0.4	1.01	0.92
	b	equal	15.9	1	1.01	0	1.01	0	0.96	0.97
2 Tolerance	All	equal	6.7	2	1.72	0.45	0.93	1.2	0.97	0.97
	a	equal	2.8	1	1.06	0.64	1.06	1.18	0.98	0.96
	b	equal	3.9	1	0.93	1.1	0.93	1.1	0.96	0.97
3 Cessation attempts	All	equal	0.1	2	1.43	0.5	1.43	0.44	0.96	0.97
4 Withdrawal	All	equal	1.4	2	3.22	1.43	1.95	1.65	0.96	0.98
5 Gambling to escape	All	equal	4.7	2	0.97	1.52	0.65	1.17	0.95	0.99
	a	equal	0.9	1	0.71	1.93	0.71	1.15	0.95	0.98
	b	equal	3.9	1	0.81	1.24	0.81	1.24	0.96	0.97
6 Chasing	All	equal	3.6	2	0.66	−0.37	1.3	0.11	0.98	0.93
7 Concealment	All	equal	3.4	2	1.7	0.81	1.12	0.61	0.94	1.01
8 Jeopardized matters	All	equal	5.3	2	2.42	1.46	1.69	1.17	0.94	0.99
	a	equal	1	1	1.8	1.63	1.8	1.17	0.94	0.97
	b	equal	4.3	1	1.92	1.23	1.92	1.23	0.96	0.97
9 Bail out	All	equal	4.1	2	3.73	1.77	1.33	2.33	0.96	0.99
	a	equal	3.9	1	1.53	2.36	1.53	2.22	0.96	0.97
	b	equal	0.2	1	1.55	2.22	1.55	2.22	0.96	0.97

¹Values exceeding 3.84 (the α = 0.05 critical value of the χ² distribution, when df = 1) are considered as significant difference (Thissen, 2001).