Table 4.

Test Statistics for Cholesky Decomposition Model for Nicotine Dependence Symptoms with Constraints across Ages

Model	−2lnL	df	Δ−2lnL (df)	p value	AIC
1. Age unconstrained model	281.54	66			149.54
2. Fully age-constrained	780.43	72	498.98(6)	<.001	636.43
3. Constrain A across age	303.73	68	22.19(2)	<.001	167.73
4. Constrain:  A: ages 18 and 21 years	281.94	67	0.38(1)	.54	145.94
5. Constrain C across age	282.12	68	0.58(2)	.75	146.12
6. Constrain E across age	471.46	68	189.92(2)	<.001	335.46
7. Constrain:   A: ages 18 and 21 years   C: all ages	282.16	69	0.62(3)	.89	144.16

Notes. Separate variance-covariance matrices were used for males and females. The unconstrained model is unconstrained across ages but is constrained across sexes. Abbreviations: A=additive genetic effects. C=shared environmental effects. E=nonshared environmental effects. −2lnL= −2 times the log likelihood. AIC=Akaike Information Criteria. Δ−2lnL=differences in 2lnL values between the sex-constrained but age unconstrained model (model 1). Best fitting model is bolded.