From Pew Research:
Same-sex marriage is now legal in Washington, D.C., and 17 states... Now the federal government’s task is to produce an accurate count of same-sex married couples.
Acknowledging a “very serious problem” of flawed same-sex marriage data, the U.S. Census Bureau is testing new marriage and relationship questions on its surveys in hopes of producing more accurate numbers in the next few years. According to a presentation earlier this month, the bureau found problems with the data “much worse” than the agency expected.
There is intense interest in the numbers and characteristics of same-sex married couples, as a growing number of states have legalized same-sex marriage and the federal government—reacting to a Supreme Court ruling last year—has expanded the rights of those couples. The numbers are important to know as a measure of how society is changing, to gauge the well-being of same-sex married-couple families and to help government agencies assess the need for various types of programs. For example, marital status can affect eligibility for some programs such as welfare and food stamps.