Sydney: Sarah Eggleton is a Sydney archetype - 40 years old, a graduate with a good job and happily single. She buys sexy lingerie, likes the idea of romance, but has decided against a permanent relationship let alone marriage and a family.

Eggleton typifies the one-quarter of Australian households that demographers call SPUDs - single person urban dwellings.

Just over half of Australia's seven million women, 51 per cent, are unmarried. A quarter of women won't have children.

Demographer Bernard Salt accounts for the singles barrage in two ways: young women delaying marriage, sometimes forever, and a new flush of baby-boomer widows. Men are packing the SPUD cohort too.

Demographer Bob Birrell says women are more discerning and so there is a greater proportion of men with poor prospects left on the shelf.

Birrell said women "prefer to have a partner who can bring substantial resources into a relationship" and that this new discernment is reflected in census data that shows that 41 per cent of men aged 30-34 and earning close to the minimum wage are in a permanent relationship.

Graham Plant of research firm Pacific Micromarketing said that a household no longer meant a couple and their kids and both business and government ought to adjust to the new realities.

"In a shifting and fragmenting consumer landscape, all enterprises need to work harder to understand their customers better," he said. "Companies should be planning products and services that their customers will want over the next decade, not what they wanted five years ago."