Table 2.

Composition of the Subgroups Based on Classification and Regression Tree (CART) Analysis at 18 Months

ADOS-G items predictive of ASD			Leaf	Leaf Label	ASD (n, %)	ATYP (n, %)	TH (n, %)	Total Leaf Size	Relative Risk for ASD (95 % Confidence Interval)
B1: Appropriate eye contact	D4: No RSB	A3: Normal intonation	A	TD	15 (12%) [7%]	36 (26%) [16%]	169 (55%) [77%]	220 [100%]	0.32 0.19 – 0.53
		A3: Somewhat odd intonation	B	ATYP	3 (2%) [27%]	6 (4%) [55%]	2 (1%) [18%]	11 [100%]	1.26 0.48 – 3.36
	D4: Some RSB	B8: Good or limited giving	C	TD	20 (16%) [15%]	43 (31%) [32%]	71 (23%) [53%]	134 [100%]	0.69 0.45 – 1.07
		B8: No giving	D	ASD	7 (6%) [70%]	2 (1%) [20%]	1 (0%) [10%]	10 [100%]	3.24 2.10 – 5.01
B1: Poor eye contact	B8: Good giving	C2: Spontaneous pretend play	E	TD	2 (2%) [4%]	15 (11%) [33%]	29 (10%) [63%]	46 [100%]	0.20 0.05 – 0.79
		C2: No spontaneous pretend play	F	ASD	12 (10%) [39%]	7 (5%) [23%]	12 (4%) [39%]	31 [100%]	1.79 1.12 – 2.87
	B8: Limited Giving	A8: Variety of gestures	G	TD	13 (11%) [33%]	12 (9%) [30%]	15 (5%) [38%]	40 [100%]	1.51 0.94 – 2.42
		A8: Limited use of gestures	H	ASD	50 (41%) [69%]	17 (12%) [23%]	6 (2%) [8%]	73 [100%]	3.17 2.54 – 3.96
			Total Outcome Group		122 (100%)	138 (100%)	305 (100%)	565	1.00 0.96 – 1.04

Note: n = 565; 20% of original sample removed for the validation set. Column marginals (proportion of all children of a particular outcome at 36 months, as given by the column header, found in each leaf) are given in parentheses (), while row marginals (proportion of children within that leaf with an ultimate diagnosis given by the column header) are given in square brackets []. Relative risk estimates for autism spectrum disorder (ASD) are based on prevalence of ASD amongst all high-risk (HR) siblings in this sample (risk compared to the general population is 14.7 times greater). ADOS = Autism Diagnostic Observation Schedule; ATYP = atypical development; RSB = repetitive and stereotyped behaviors; TD = typical development.