Researchers are gaining insight into the marijuana economy - by collecting data from users themselves.

A team that includes a University of Arizona Ph.D. candidate used online price data supplied by marijuana users to create and analyze a map showing the retail price of marijuana throughout the country.

The resulting data give researchers a rare glimpse into an underground economy that is large enough to have social, economic and public policy implications but has been largely "unstudyable," said Monica Stephens, a Ph.D. candidate in the UA School of Geography and Development who is part of the research team.

People make assumptions about underground economies with little information on how they actually work, Stephens said.

In the case of marijuana, the effects of enforcement and medical marijuana policies in different states can be difficult to track.

Other studies on retail marijuana tend to be small and local, Stephens said, while most data supplied by the government are vague and national.

But an increase in online user-generated content, or data provided by website visitors, may help researchers track trends in areas that otherwise have little data, Stephens said.

"I think the future is massive," she said.

Information the researchers gathered became a paper, "Data Shadows of an Underground Economy: Volunteered Geographic Information and the Economic Geographies of Marijuana," that aims to draw state-level conclusions about the map by comparing price to other factors such as the perceived strictness of law enforcement and social acceptance of marijuana use, as well as medical marijuana programs in the state.

The team also used the number of eradicated marijuana plants in a state to gauge production.

The researchers found that the medical marijuana program in a state had the largest influence on the price but perceived strictness of law enforcement had little effect. While much of the national data on marijuana are obtained when law enforcement intersects with this underground economy, user-generated content provides information on the day-to-day operations, Stephens said.

The work is being done by a team of geographers from Floating Sheep, an organization studying the "geo-coded," or location-specific, information people post online.

The researchers used the website Price of Weed to gather prices users said they paid for high-quality marijuana in cities throughout the country.

Floating Sheep, which was founded by an associate professor at the University of Kentucky but is unfunded, previously plotted bars across the nation and compared the number of bookstores and churches in an area. As it did with Price of Weed, the organization uses information supplied by users online.

"User-generated content is a quite accurate source of information," said Stephens, who has been researching at the University of Kentucky since January. "It's more reviewed, more accurate. Those maps are more accurate than what the government has."

That would only be true if the data entered on the site were accurate - and that might not be the case, said Anthony Coulson, former Drug Enforcement Administration assistant special agent in charge of the Tucson District Office.

The average retail price for marijuana in Arizona ranges from $300 to $500 a pound, Coulson said, but the team's research found it to be $353.90 an ounce for high-quality marijuana.

The irregularities in price could be a sign of people spamming the site, he said.

Websites such as Price of Weed may provide insight to researchers, but they pose concerns to law enforcement, said Ramona Sanchez, a DEA spokeswoman in Phoenix.

The DEA often contacts people hosting these websites to have them taken down, Sanchez said. The DEA has also launched investigations into several drug-related websites, she said.

"They claim responses are anonymous," Sanchez said. "But when it comes to the Internet, there's no such thing as anonymity."

While she said the DEA is familiar with Price of Weed, she would not comment on it specifically.

The increase in user-generated content may point to its future in helping researchers delve into topics from drug use to terrorism, Stephens said.

"It's a growing and bubbling field," she said. "There's a lot going on."

Conclusions

Marijuana is cheaper in areas of production, such as Humboldt County, Calif.

Proximity to production areas is also a key factor. The researchers used Humboldt County, Calif., as the main production site in the U.S. Price increased the farther a state was from Humboldt County.

For Tucson, proximity to Mexico is a factor. However, marijuana from Mexico tends to be classified as lower quality.

States that have legalized marijuana have lower retail prices than states that haven't, possibly because some of the demand is supplied legally.

Marijuana tends to be cheaper in states with higher rates of obesity.

Marijuana is more expensive in places that have more bars per capita.

By the Numbers

22,365

the number of price reports Price of Weed received from September 2010 to March 2011.

2,397

the number of U.S. cities represented in price report submissions.

$377.02

the average retail price for an ounce of high-quality marijuana in the U.S., as calculated by the researchers.

$353.90

the average retail price for an ounce of high-quality marijuana in Arizona, based on 170 records.

16

The number of states that have legalized medical marijuana.

Sources: Data Shadows of an Underground Economy: Volunteered Geographic Information and the Economic Geographies of Marijuana and Monica Stephens