Figure 2.
Participation flowchart, cohorts combined. (See Supplementary File 1 for cohort-specific participation flowcharts, available as Supplementary data at IJE online.)
Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.