I was recently looking at Money‘s 2012 list of the 2012 Best Places To Live and noticed something strange: they report family income and not household income. For example, look at the figures for Naperville, Illinois, #53 on the list (how Naperville has fallen so far on this list after being very near the top less than 10 years ago is another topic for another day): the median family income is $123,511.

Why does this matter? The median family income is generally higher than the median household income because the first only counts households with relatives living together while the second can include single-person households (as well as households with roommates and non-relatives.) This is not a small issue: tied for the most common household type in the United States today is the single-person household.

According to 2011 census data, people who live alone–nearly 33 million Americans–make up 28% of all U.S. households, which means they are now tied with childless couples as the most prominent residential type, more common than the nuclear family, the multigenerational family and the roommate or group home. These aren’t just transitional living situations: over a five-year period, people who live alone are more likely to remain in their current state than anyone else except married couples with children.

Perhaps Money‘s readers are primarily in family households but this still skews the data for the best place to live. Perhaps the feature should really be called the “Best Places for Families to Live”?