You are about to leave a SAMHSA-funded website. SAMHSA provides links to other Internet sites as a service to its users, and is not responsible for the availability or content of these external sites. SAMHSA, its employees, and contractors do not endorse, warrant, or guarantee the products, services, or information described or offered at these other Internet sites. Any reference to a commercial product, process, or service is not an endorsement or recommendation by the SAMHSA, its employees, or contractors. For documents available from this server, the U.S. Government does not warrant or assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed. The National Academies Press