"Knock-knock Whose's there? The census-taker Go go away!"

Ten years ago, huge wolf-like dogs frightened census-taker Lu Yaqin. Today, the fierce guards have been replaced by little yappy dogs, but residents' wariness, lack of cooperation, hiding and sometimes untruths make the job a minefield where census-takers must be strong, patient and resourceful.

This year the intrepid census-takers are even using GPS and satellite imagery to make sure they don't miss a single shantytown or dwelling out in the suburbs.

Lu, 55, worked as a census-taker 10 yeas ago when, it seemed, people had less to hide, fewer assets, fewer children, fewer people living in the house - but today they have much stronger sense of privacy and more secrets.

Lu has again jointed China's millions of census-takers, going door to door with a basic 18-question sheet; longer forms (taken by 10 percent chosen at random) contain around 80 questions, covering education, reason for moving and other queries.

The 10-day register starting November 1 will go through tomorrow.

Sometimes the doors are slammed, sometimes no one answers the bell, though there are lights and noise inside. She has come back, sometimes with an invitation, only to find the owners have vamoosed. Sometimes people just tell her she's a busybody and they're too busy.

To appease and reward reluctant residents who answer the longer forms, they may be given small gifts, such as a hand towel or a pair of manicure scissors.

What they don't ask: cost of the home, value of the home, how many other homes are owned, income, specific employment, and some other touchy questions. No one wants the census to lead the taxman to visit.

The 2000 census asked about the value of residence. Samples in 2005 asked about personal income.

This year they do ask the obvious: do they own a home, how many rooms, how many people in the family and how many children. If they have "extra" child or children beyond the standards "one child," they can pay a reduced penalty fee if declared during the census. They are asked how many hukous (residence permits) in the family, how long a couple has been married. One man living with his second wife was enraged and refused to answer questions about his first wife.

Census-takers want to find out how many men China has and how many women (the demographics has been skewed for years because of male preference).

They are making a special effort to find out about migrant workers (both in their new homes and old hometowns in the countryside) and who has hukou and who doesn't.

Back in 2000, Lu was a village official in Pudong's Gaodong Town where she visited nearly all 200 households; since then she has retired but she recalls vividly.

"Some villagers raised huge guard dogs in their yards," she recalled. "The animals rushed out and barked at me when I was trying to get in. I had to call for help before they bit me."

Today, Gaonan Village where Lu lived has been replaced by a cigarette factory, and Lu has moved into Pudong's Yinqiao neighborhood. Again she is offering a volunteer hand in the census, China's 6th.

Lu was surprised that this time she also had trouble getting inside the modern residential complex.

"People are getting busier and busier," she said. "It's hard to find them now." She visited some houses several times in one day, but still could not find the owners.

It's quite odd that half the apartments in a building don't show a single light turned at 8pm or 9pm, she said. Some gave her a raft of excuses. Some just said she was a busybody.

"I fully understand," Lu said. "Fast-paced living leaves many people strapped for time, and sometimes in a bad mood after work."

But even when she does sit down with families, they balk at some questions.

Ten years ago she knew all the families in her village and was often invited for a chat and a snack. No more.

"But the situation is different in the big community with a transient population now," she said. "I don't know many residents since they move in and out quickly."

Many residents don't want to talk about floor area and underestimate it. Many don't like to say how many living under one roof and how many have hukou. Many don't like being asked their occupation. Many expats don't like being asked their age.

Lu is not alone. Her frustrating experiences are shared by many other census-takers nationwide. Every census-taker covers 80-100 households.

Census information will be used by the government to develop plans for distribution of schools, kindergartens, elderly care centers and hospitals and to plan housing construction.

"Census-takers can face difficulties in getting families with unregistered children (usually over the one-child limit for many families) to share personal information, especially about the child," said Gui Shixun, professor with the Population Research Institute at the East China Normal University in Shanghai.

"Parents with children born in violation of China's one-child family planning policy (loosened in some cases, including when both parents are single-children) are required to pay a heavy fine," he explained.

Many other people don't want to open the door; these include migrants living in extremely crowded spaces that exceed the government limits of their group rent.

Meanwhile, some residents worry that the census will lead to property tax, so many underestimate total floor area and rooms.

China's last census in 2000 showed the population at 1.265 billion; it estimated 64 percent, or around 800 million, were living in the countryside.

In the 10 years since the last head count, there has been an enormous demographic shift, since 10s of millions of migrant workers have poured into urban areas looking for work. But the populations in China's giant cities thus far have only been estimates.

Shanghai, the country's most populous city, has seen a big increase in the migrant population.

Large-scale relocation has caused local residents to be separated from their household registration (which remains back in their rural hometowns) which includes benefits in getting into school, health care and other advantages.

The complicated situation made the census-takers' task tougher than in previous years.

Faced by widespread reluctance to answer questions, the government has reiterated through the media that census results will not be used to any assessment of awards or punishment.

Census reports will be confidential and will be destroyed after data processing ends. All census staff are sworn to confidentiality.

"The census paper cannot tell how many apartments a person owns," Professor Gui said.

Income is not on the questionnaire.

Despite government promises, residents still feel worried about privacy leak.

Most of the census workers are employees of local district governments, members of neighborhood committees and community residents.

"I believe census-takers will not deliberately leak the information," said resident Edward Dai.

"But it's likely that they accidentally give some information away in chatting with others."

He said that, possibly as a result of the census, he had been bothered by lots of phone calls and mails asking him to sell his apartment or buy insurance. "They knew my name, address and basic family information. I don't know where they got it from," he said.