  Recent studies have shown that information mined from Craigslist can be used
for informing public health policy or monitoring risk behavior. This paper
presents a text-mining method for conducting public health surveillance of
marijuana use concerns in the U.S. using online classified ads in Craigslist.
We collected more than 200 thousands of rental ads in the housing categories in
Craigslist and devised text-mining methods for efficiently and accurately
extract rental ads associated with concerns about the uses of marijuana in
different states across the U.S. We linked the extracted ads to their
geographic locations and computed summary statistics of the ads having
marijuana use concerns. Our data is then compared with the State Marijuana Laws
Map published by the U.S. government and marijuana related keywords search in
Google to verify our collected data with respect to the demographics of
marijuana use concerns. Our data not only indicates strong correlations between
Craigslist ads, Google search and the State Marijuana Laws Map in states where
marijuana uses are legal, but also reveals some hidden world of marijuana use
concerns in other states where marijuana use is illegal. Our approach can be
utilized as a marijuana surveillance tool for policy makers to develop public
health policy and regulations.
