According to the National Association of Realtors, married couples were buyers in 61 percent of all housing purchases last year.  Single women represented the second largest share of the market, purchasing 21 percent of homes and condos in 2005, up from 18 percent in 1997. 

Single men accounted for 9 percent of residential real estate transactions.  Unmarried couples were involved in 7 percent of housing purchases. Joint purchases by other unmarried people accounted for the other 2 percent.

Who are these single women?  Why are they buying real estate in such large numbers?  And how do they differ from single men and married couples?

The answers to these questions are found in a new report -- "Buying for Themselves: An Analysis of Unmarried Female Homebuyers" -- released two months ago by the Joint Center for Housing Studies at Harvard University.

The Harvard report characterizes unmarried female buyers as "a diverse and highly segmented group comprised of single mothers, young singles, middle-aged divorcees and seniors" who purchased more than $550 billion in real estate between 2000 and 2003.

"Unmarried female buyers are older than married and unmarried male buyers, have higher shares of minority buyers, have lower incomes and, consequently, much greater incidence of housing affordability problems," the report says.

But despite affordability problems experienced by single women, their share of the market has dramatically risen while the share of married couples has dropped sharply.  The report gives several reasons for this trend:

* A 20 percent increase in the number of unmarried women in the past decade, partly due to the fact that women are delaying marriage in favor of education and careers.

* Fewer adult women than men chose to live with their parents, opting to form their own households instead.

* The economic upside of owning -- which has been emphasized heavily by the media -- enhances the view of a growing number of women that marriage is no longer a pre-requisite to buying a home.

* Divorced women have accumulated equity in homes they owned with spouses and can use that wealth to buy their own homes as their set up their own households.

Previously married women accounted for nearly two-thirds of unmarried female buyers while more than half of unmarried male buyers have never been married.  This partially explains the younger average age of male buyers (37) relative to unmarried female buyers (42).

Another major difference between single male and female buyers is their living arrangements.

Among buyers profiled in the Harvard report, about 45% of single women lived alone, compared to 55 percent of single men.  Only 15 percent of the men are single parents, in contrast to 30 percent of the women.

Unmarried female buyers have considerably lower incomes than single men who buy homes.  "Their $37,000 median income is fully $11,000 less than for unmarried men," the report states.

Although unmarried adults of all types have had a combined market share of nearly 40 percent of home purchases for the past several years, real estate developers and marketers are only now beginning to notice the value of the "single dollar."

According to the Harvard report, one developer in Southern California has targeted single women by offering amenities they prefer, "including smaller units, gated access, fitness facilities, social interactions with neighbors, and other organizational and convenience features."

KB Home, a home builder in Cary, North Carolina, is targeting single men as potential buyers of its new condominiums.  The condos were designed with the single male in mind: stone floors, stainless steel appliances and glass-walled showers instead of tubs in the master bathrooms. 

While single people are still more likely to be renters than owners, that reality is changing.  One of the reasons singles are shifting from renting to owning is the tax breaks associated with home ownership: the ability to write of tax and interest payments.

So all you single renters, listen up.  Buy now and lower your tax bill come April 2007.