The federal estimate seems very conservative. The National Survey on Drug Use and Health reported somewhat higher rates of marijuana use last year in legal and decriminalized states. But is use really going up? Or, relieved of criminal prohibition, are people more willing to be honest on a government survey? My sense is the latter. Still, for the purposes of our exercise, we will use the low trending number supplied by the federal government along with RAND's suggestion to adjust it higher by 20 percent.