Table 4.

Wald test results for item difficulty by gender and age.

	Gender		Age
	z-Statistic	p-Value	z-Statistic	p-Value
Gastrointestinal tract
gurgle	−0.51	0.613	2.58 *	0.010 *
stool color	−1.17	0.242	0.29	0.769
stool form	−0.23	0.817	−0.70	0.485
stress	−0.53	0.598	−1.10	0.273
statement	0.40	0.691	−0.91	0.366
Abdominal Pain
perception	0.03	0.976	0.02	0.988
doctor	0.25	0.802	0.62	0.539
types	1.66	0.097	−1.54	0.124
obstipation	0.61	0.543	0.39	0.702
food poisoning	−0.63	0.527	−2.16 *	0.031 *
Functional Abdominal Pain
answer	0.36	0.718	0.23	0.818
influence	0.12	0.914	−1.08	0.279
limitation	−1.23	0.219	1.22	0.224
soccer	−0.08	0.938	2.24 *	0.025 *
medication	−0.06	0.949	−0.76	0.449
Handling FAP
help	0.77	0.440	2.18 *	0.030 *
nutrition	0.42	0.678	1.44	0.149
warmth	1.80	0.071	−1.40	0.161
sleep	0.88	0.381	0.78	0.434
distraction	−2.19 *	0.028 *	−0.56	0.576

Negative values indicate that the item is easier for girls compared to boys or for older compared to younger patients. * Statistically significant difference in item difficulty between the two groups, and thus a divergence from the model (p < 0.05).