While Kim Hay, the woman given as an example, is a self-identified single woman, it is offensive and ignorant to take a statistical sample and determine that all women who are not legally married are "single." This devalues committed-but-not-legally-married relationships, both of same-sex couples and other-sex couples.
The American Psychological Association's Style Guide (by which authors submitting papers to most of the major psychology and sociology journals must abide) gives the following guideline:
Omitting discussion of marital status unless legal marital relationships are the object of the writing. Marital status per se is not a good indicator of cohabitation (marital couples may be separated; unmarried couples may live together), sexual activity, or sexual orientation (a person who is married may be in a gay or lesbian relationship with a partner). Further, describing people as married or "single" renders lesbians, gay men, and bisexual persons as well as heterosexual people in cohabiting relationships invisible.
It isn't clear from the article whether the statistics as presented by the National Association of Realtors specified whether their numbers referred to self-identified single females or to females who are not legally married. It is clear that Christina Wallace (and/or whomever chose the statistics) seems to view these terms interchangibly. It seems logical that the "number of unmarried females owning homes" would be derived from mortgage and property ownership data. Obviously, these figures only take legal status into account; there is no way of determining whether these unmarried women owning homes are single or partnered. The assumption that all of these unmarried women are single is of course not at all realistic.
I am not legally married and am the sole legal owner of a home -- I don't like that I may have in fact been counted in the "single women owning a home" statistic, since, well, I'm not single.
Even if the National Association of Realtors did in fact organize actual data collection in which Realtors reported on the numbers of sales they made to single and married women, this data collection is still not sound, because it excludes the category of women who are in non-married committed partnerships. It also relies on the judgment of the Realtor to determine which clients s/he is going to count as "single" or "married." I doubt that the Realtor is going around asking clients their marital status; I do know that when I bought my house, I took care of most of the mortgage processing myself, so he didn't ever see a credit report or anything that would indicate my legal marital status. Therefore it would have been up to him to decide whether he thought I was "married" or "single" if given only those two choices in a survey.
Actually, now that I mention my Realtor, it's too bad he wasn't the Realtor interviewed, since he would have given equal treatment to the partnered couples and single people he's worked with instead of furthering the "people are single unless in a hetero marriage" slant of the story.
If the author wishes to discuss the trend of actual single women buying homes -- which I do find sociologically interesting -- she might want to stick to interviewing self-identified single women or taking a poll in which homebuyers can self-identify in terms of their relationship status. The legal marital status of people buying homes really isn't interesting; I doubt anyone is going around asking to see their neighbors' marriage certificates. The actual status of people buying homes is interesting, and is what really makes up a neighborhood. Kim Hay's personal story of her decision to buy a house is much more interesting than misleading statistics anyway, and isn't offensive like the overgeneralizing and invisibilizing is.