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.
The percentage of urine samples negative for opiates (top graphs), cocaine (middle graphs), and both opiates and cocaine (bottom graphs) during the monthly (left panel) and thrice-weekly (right panel) assessments. The data points represent individual participants and the horizontal lines indicate condition means. The study was conducted in Baltimore, MD from December 2008 to December 2012.
