Table 10. DSM–IV Generalized Anxiety Disorder Item-by-Item Tests for Effects of Age and Study Together on Factor Loadings.

Model	−2LnL	Δχ2	Δdf	AIC	Age effect	Study effect
Age and study on latent variance (baseline)	14,241.73			−14,570.27
Item free
Did your muscles often feel tense, sore or achy?	14,237.83	3.90	2	−14,570.16	.12	−.12
Did you often tire easily?	14,229.23	12.50**	2	−14,578.77	.28	.11
Were you so nervous you had trouble concentrating?	14,228.01	13.72**	2	−14,579.99	−.10	.17
Did you often have trouble falling asleep?	14,239.79	1.94	2	−14,568.21	−.06	.08
Were you often irritable or especially impatient?	14,215.61	26.12***	2	−14,592.39	−.37	−.15
Did you feel restless or keyed up and on edge?	14,235.02	6.71*	2	−14,572.98	.26	−.16

Note. N = 6,426. The most parsimonious model is shown in boldface. DSM–IV = Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition; AIC = Akaike information criterion.

^*p < .05.

^**p < .01.

^***p < .001.