Table 6. DSM–IV Generalized Anxiety Disorder Item-by-Item Tests for Effects of Age and Study Together on Thresholds.

Model	−2LnL	Δχ2	Δdf	AIC	Age effect	Study effect
Age and study on latent mean (baseline)	14,243.31			−14,568.68
Item free
Did your muscles often feel tense, sore or achy?	14,234.02	9.29*	2	−14,573.97	−.06	.22
Did you often tire easily?	14,223.82	19.49***	2	−14,584.18	−.69	−.05
Were you so nervous you had trouble concentrating?	14,222.31	21.00***	2	−14,585.69	.23	−.35
Did you often have trouble falling asleep?	14,237.39	5.92	2	−14,570.61	.05	−.18
Were you often irritable or especially impatient?	14,204.62	38.70***	2	−14,603.38	.49	.34
Did you feel restless or keyed up and on edge?	14,232.75	10.56**	2	−14,575.25	−.33	.33

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.