The first rule of being a decoy homeless person: Don’t talk about being a decoy homeless person. Also, don’t read books the homeless wouldn’t read, and don’t haggle with real homeless people over their prime hangout spots.

Those were among the instructions officials gave almost 200 people getting paid about $75 each to pretend to be homeless for a few hours yesterday morning. The decoys were acting as statistical checks-and-balances in the fifth annual citywide census of how many homeless people live on the streets and in the subways.

For every decoy the city misses, researchers make a statistical assumption that they’ve missed a proportional number of actual homeless people.

Using the decoy method, statisticians last year found more than 3,800 people were homeless on the city’s streets. The figure doesn’t include individuals in shelters, which is a much higher number. So it was a social-services game of cat-and-mouse early yesterday morning, with almost 3,000 volunteers hunting down some 200 decoys secretly scattered across the city.

“They’re supposed to look and act as homeless as possible so that it’s really hard to differentiate,” a spokeswoman for the city Department of Homeless Services, Linda Bazerjian, said.

To help the decoys look as homeless as possible, Columbia University’s School of Social Work supplied the props, including dirty, folded up cardboard boxes the decoys picked from and carried to their assigned spots.

Divided in small teams, the census takers were instructed to ask everyone they suspected was homeless whether they had a place to sleep. Decoys discovered by surveyors were instructed to disclose their true identity by flashing a florescent sticker, and they then could go home.

Before they could disclose anything, they had to get their assignments at Columbia. The decoys arrived hours before deployment to get their assignments and transform into homeless chic. Most couldn’t wear their everyday attire. Some were still wearing the cloth of privilege, such as Abercrombie & Fitch lambs wool sweaters and North Face fleeces. Decoy Joseph Butler, who lives in the South Bronx, was assigned to the 1, 2, and 3 subway lines at 42nd Street, where he lived when he was homeless for three years in the 1990s.

“I know every subway station — every nook and cranny,” Mr. Butler said.

A professor at the Columbia University School of Social Work, Julien Teitler, said many of the decoys gain an appreciation for what it’s like to be homeless.

If some of the decoys were subjecting themselves to the winter cold for the goodness of their hearts, others were there purely for the cash.

One of them was a costume designer and theater student named Elizabeth Cassarino, who said unabashedly that she didn’t care about the homeless. She planned to use the $75 to buy food and cigarettes.

“I know what goes into being a character. So for this role, playing a homeless person, you have to have the right costume — baggie clothes, layers — you have look sad, you have to play like you’re homeless. You can’t have a smile on your face. You have to do emotional recall, think of a time when you were hungry,” Ms. Cassarino said before deployment. “These are all the things they taught me in school, and now I’m actually getting a chance to perform. You know, my audience is going to be the people waiting for a train at Broadway and Lafayette.”

Every decoy got a partner, and the 42-year-old Ms. Cassarino described hers, Columbia undergraduate Erik Saari, as a David Hasselhoff look-alike.

Mr. Saari, who is in his 20s, said he wasn’t a decoy for altruism. “75 bucks — and that’s pretty much it,” he said.

Most of the other dozen students interviewed before deployment said they’d volunteered to be decoys to do their small part to make a difference.

As midnight neared, homeless decoys trickled out of the Columbia social work building to deploy. A half-dozen young women in bum chic, with gratis MetroCards and prop cardboard boxes, boarded a South-Ferry-bound 1 train.

Somewhere between the 116th and 59th street stops, a non-decoy beggar named José Reyes stumbled into the subway car. He told passengers he was starving for food. He begged for change. The $75-a-night fake homeless people couldn’t spare a dime.