Table 3. Genetic model-fitting results for cervical smear.

	Model	−2LL	df	vs	χ2	Δdf	P	AIC	a2	c2	e2
1	Full ACE	2302.350	2688					−3073.650	0.37	2.6−10	0.63
2	E model	2315.051	2690	1	12.701	2	0.002	−3064.949	—	—	1.00
3	CE model	2304.188	2689	1	1.838	1	0.175	−3073.812	—	0.23	0.77
4	AE model	2302.350	2689	1	0	1	1.000	−3075.650	0.37	—	0.63

Abbreviations: −2LL, −2 log likelihood; χ², by substracting the −2LL of two different (nested) models yields a statistic that is asymptotically distributed as χ²distribution; AIC, Akaike's Information Criterion: a lower value of AIC indicates a more parsimonious model; df, degrees of freedom; Δdf, difference in degrees of freedom between two models; P, P-value; vs, tested versus model.

Cervical smear results were categorized in no abnormalities, mild abnormalities and severe abnormalities. Thresholds (=prevalences) were allowed to vary with age group (<40 or ≥40 years) and year of diagnosis (<1996 or ≥1996). a², additive genetic influences; c², common environmental influences; e², unique environmental factors.