Table 1. Older Sibling Information for Each of the 20 High-Risk Infants in Our Study.

“Outside Clinical Diagnosis” was made by an outside clinical professional in the community, usually when the child was under age three. A “Clinical Best Estimate Diagnosis” was made by our clinical psychologist (N. Akshoomoff) based on information from research diagnoses (ADOS and ADI-R) and clinical judgment using DSM-IV-TR criteria. There was sometimes a difference between the original outside clinical diagnosis and our Clinical Best Estimate Diagnosis, which is consistent with previous studies demonstrating that change in diagnosis is most likely to occur between the ages of two and five (97, 98).

Subject	Gender	Age at Outside Clinical Diagnosis	Original Outside Clinical Diagnosis	Age at Clinical Best Estimate Diagnosis	Clinical Best Estimate Diagnosis
S1	M	2 yr, 10 mo	AD	4 yr, 11 mo	AD
S2	M	2 yr, 4 mo	PDD	4 yr, 8 mo	PDD
S3	M	2 yr, 1 mo	AD/DD	5 yr. 3 mo	AD
S4	M	2 yr, 8 mo	Autism	5 yr, 5 mo	AD
S5	M	2 yr, 6 mo	AD/Mild MR	7 yr, 2 mo	AD
S6	F	22 mo	Provisional PDD	4 yr	AD
S7	M	2 yr, 7 mo	PDD (HF)	3 yr, 2 mo	PDD
S8	M	16 mo	AD	5 yr, 8 mo	AD
S9	M	2 yr	Provisional AD	4 yr, 9 mo	AD
S10	M	4 yr	PDD	7 yr, 6 mo	AD
S11	M	--	None	5 yr, 2 mo	PDD
S12	M	5 yr, 6 mo	AD/MR	16 yr, 9 mo	AD
S13	M	2 yr, 11 mo	AD	3 yr, 9 mo	AD
S14	M	2 yr, 5 mo	AD	3 yr, 11 mo	PDD
S15	M	3 yr, 5 mo	Mild ASP	4 yr, 11 mo	AD
S16	M	2 yr, 9 mo	AD	5 yr	PDD
S17	M	3 yr, 4 mo	AD	7 yr, 3 mo	PDD
S18	F	3 yr, 9 mo	AD	5 yr, 5 mo	AD
S19	M	21 mo	AD	6 yr, 6 mo	PDD
S20	M	20 mo	AD	2 yr, 6 mo	AD

AD = Autistic Disorder, ASP = Asperger’s Disorder, PDD = Pervasive Developmental Disorder Not Otherwise Specified. N/A = Not available for research diagnosis, and thus no clinical best estimate could be made.