For generations, pro-marijuana Californians have hid their dope preference from their parents, their teachers and their co-workers.

And now, perhaps, from their pollsters.

The campaign team behind Proposition 19, which is working to legalize, tax and regulate marijuana for Californians over 21, has noticed an odd trend among public and internal polls on the measure: People are less likely to tell a live person that they support legalizing pot than an automated pollster.

It's reminiscent of 1982, when state voters told pollsters they wouldn't have any problem supporting Tom Bradley as the state's first African American governor. But when they entered the voting booth, enough of them voted instead for George Deukmejian that Bradley lost as a result of what has been dubbed the "Bradley Effect."

National pollster Nate Silver calls the Prop. 19 version of this "The Broadus Effect" - after weed-loving Calvin Broadus, a.k.a. rapper-actor Snoop Dogg. The "Broadus Effect" adds another layer of intrigue to an already mysterious demographic: supporters of legalized marijuana.

Nobody can say how many are out there - and how many will vote.

It can be challenging to survey voters on socially controversial issues such as same-sex marriage and drugs, where people may be reluctant to share their views without "feeling as though they're being judged," said Scott Keeter, director of survey research at the Pew Research Center.

"Men - especially younger men - are less likely to be supportive when they're talking to a live pollster," said Ruth Bernstein, the Oakland pollster for Prop. 19. "The polling we're seeing is telling us that there is something going on here, but we're not quite sure what it is yet."

Bernstein was so curious that on Oct. 13-14, the campaign ran side-by-side polls - one using live questioners, the other using automated voices. When a live person asked, 41 percent of the respondents favored legalizing pot, but when asked by an automated questioner, 56 percent said they supported legalization, according to the internal poll.

Among men, 42 percent told a live interviewer they backed legalization - but 61 percent backed legalizing dope to an automated questioner.

Support for Prop. 19 has slipped recently in public-opinion polls, with a Public Policy Institute of California survey last week showing 44 percent of likely voters supporting it to 49 percent opposed. The month before, the survey found 52 percent support.

Public Policy Institute of California CEO Mark Baldassare was skeptical of a "Broadus Effect."

"There's a difference in telling someone you support changing a law - and what you are doing yourself. There's no social stigma involved in changing a law."