FIGURE 1.
Overview of the study. Numerals (1, 2, etc.) show what population is used for analysis described in the Material and methods section.
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.