6 months to a year between the Vanguard sites data collection and the collection of data by all the sites would be beneficial. The increase in time should be implemented not only for the first phase of enrollment through age 24 months, but also for the introduction of each new set of operations and instruments for subsequent 3-year periods throughout the life of the study. In addition, we encourage the NCS to build in experimentation with instruments and study procedures into the Vanguard operations when the extant literature is not sufficiently clear about the preferred approaches.

Recommendation 2-4: We strongly urge the NCS to delay enrollment at new sites to make effective use of initial findings from participant enrollment and data collection in the Vanguard Center sites to improve study procedures, as appropriate, and to refine key concepts, hypotheses, and measures of outcomes and exposures. Throughout the life of the study, the NCS should use the Vanguard Centers to pilot test and experiment with data collection methods and instrumentation.

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