Table 1.

Methods of measuring onset

Assessment Instrument	Informant	Timing	Type
Session Summary Report	Examiner	Prospective	Dimensional
EDQ - Part 1	Parent	Prospective	Dimensional
EDQ - Part 2	Parent	Prospective	Categorical
Autism Diagnostic Interview-Revised	Parent	Retrospective	Categorical

Note: EDQ = Early Development Questionnaire

Prospective = rated at each visit

Retrospective = rated at the end of the study (36 months)

Dimensional = frequency of social behaviors

Categorical = presence or absence of skill decline or loss