An official website of the United States government 
This brief describes strategies for tracking members of a study sample throughout enrollment and data collection.
An official website of the United States government Here’s how you know
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.
