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Seventy cents. That's how much you are worth to NZ Post when it sells your details to direct marketing companies.

The details, which include phone number, address and email, are gleaned from the Lifestyle Survey, which has landed in 800,000 letterboxes around the country in the past month. One lucky participant will win a $15,000 cash prize.

NZ Post, which is a state-owned enterprise, made $1.1 million from renting the lifestyle database and others last year.

Other databases are created from information gleaned from change of address forms, PO Box details and vehicle registrations - if you tick the box at the bottom of the form, you are part of it.

The lifestyle database was considered by industry experts to be the most reliable and comprehensive source of consumer information in New Zealand.

From the responses to 56 questions, NZ Post can draw a detailed picture of a person's interests, lifestyle, monthly spending, donations, utilities and, importantly, how satisfied they are with the providers.

Clients tell NZ Post who they want to target - women aged 18 to 29 who are planning to get married in the next 12 months and who have children younger than 12 years old, for example. NZ Post has the details for 1119 women fitting this specific criteria up for sale.

Among the clients who have bought NZ Post survey data are New World supermarket, AA Life Insurance, Auckland Regional Transport Authority, Dunedin City Council, Dunlop tyres, Cafe L'affare, Family Planning, Geeks on Wheels, banks like ASB and BNZ and charities like St John Ambulance and the Heart Foundation.

NZ Post's commercial services manager Lindsay Welsh said allowing companies to "buy a relevant audience" meant everyone was better off.

"It's about talking to the people who want to hear your message," he said.

Companies wanting to buy the lists were screened according to a "strict criteria" - which ensured information did not end up in the hands of offshore Viagra merchants or lottery scams, said communication manager John Tulloch.

Marketing Association public affairs manager Keith Norris said a limitation of the survey results was people tended to look at themselves through "rose-coloured spectacles".

NZ Post is not the only port of call for a company seeking comprehensive consumer information. An extensive range of data is also available for businesses at Statistics New Zealand - but it does not sell private information identifying individuals' names and addresses.

Statistics NZ has an online Business Toolbox on its website that allows anyone to locate areas containing a particular type of person - such as high-income families with children, or young apartment-dwellers with disposable income. Government statistician Vina Cullum said the department could respond to customised requests, and charged on a "cost-recovery basis".

AUT University marketing and advertising lecturer Dave Bibby said businesses could use such data to effectively capture a specific audience.

"If I wanted to find Mormon females earning $100,000 a year it would show me the streets to door-knock," he said.

Bibby, one of the country's leading experts on targeted marketing, said there was nothing insidious about the Lifestyle Survey - NZ Post was transparent about its purpose.