Table 4.

Study to Explore Early Development design-based research strengths

Feature	Advantage
Multisite	Multiple U.S. sites located in diverse communities improves generalizability of SEED findings to the broad U.S. population compared with studies performed in single areas.
Multisource ascertainment	Identification of potential ASD and DD participants from multiple facilities at each site improves representativeness of the full range of children with autism in each study area by diminishing biases that could arise from limiting study families to those who are seen only at single facilities.
Ascertainment of diagnosed and undiagnosed ASD children	Actively recruiting children who did not have a previous autism diagnosis but met SEED’s rigorous autism case definition improves representativeness of ASD group in SEED’s target preschool age range because not all affected children might have received an autism diagnosis from community providers by the time of SEED enrollment.
Two comparison groups	The DD (children affected with developmental problems other than autism) and POP (children drawn from the study population of births, most of whom have typical development) comparison groups are designed to control for potential recall bias among ASD parents and to more accurately distinguish features of autism from both typical development and other developmental problems.
Uniform study protocol across sites	Uniform eligibility criteria and data collection protocols, including final participant classification procedures, and robust quality control measures: Ensure high intrasite and intersite data collection and developmental assessment reliability. Enhance quality and precision of the multisite pooled data. Enhance size of the multisite pooled analytic sample.
Large sample size	The final sample size will be among the largest of autism epidemiologic studies planned to date, resulting in: Robust study power based on the total pooled analytic sample. Good power for analyses based on key ASD subgroups and common (≥5 % prevalence) risk factors.
Data collection redundancy	Some data are being collected under different modalities (e.g., self-report and medical record abstraction). This will: Better ensure certain classes of risk factor information are not missed. Permit assessment of data retrieval and quality across different data collection modalities.
Enrollment of participants who speak only Spanish	Two sites are actively recruiting families who speak only Spanish to accommodate the large Hispanic population in their study areas. This will greatly inform the future development of appropriate autism study methods and improvement of autism instruments for Spanish-only speakers.
Use of both existing and novel CADDRE-derived instruments	Assess feasibility and performance in large, population-based research setting of both existing standardized instruments (performance of many instruments has not been assessed outside smaller clinical research applications), and CADDRE-derived novel instruments and approaches for special data types (e.g., stool, diet, and dysmorphology assessment)