From page 247-248

TECHNICAL NOTE ON SAME-SEX UNMARRIED PARTNER DATA FROM THE 1990 AND 2000 CENSUSES

...In 1990, the edit and allocation procedures did not allow same-sex “spouse” combinations to occur, thus resulting in the allocation of one of these two items in order to achieve editing consistency among the responses.

...Processing steps were changed for Census 2000 for households that contained same-sex “spouses.” If the person with the “spouse” category was the same sex as the householder and if neither person had their sex previously allocated, a relationship response of “spouse” was allocated as an “unmarried partner” response.

...Two principal factors affected our decision to take this approach for Census 2000.

1.      Marriage Act (H.R. 3396) passed by the 104th Congress. This act instructs all federal agencies only to recognize opposite-sex marriages for the purposes of enacting any agency programs. In order for Census Bureau data to be consistent with this act and the data requirements of other federal agencies, same-sex spouse responses were invalidated. The legislation defines marriage and spouse as follows:

 “In determining the meaning of any Act of Congress, or of any ruling, regulation or interpretation of the various administrative bureaus and agencies of the United States, the word ’marriage’ means only a legal union between one man and one woman as husband and wife, and the word ’spouse’ refers only to a person of the opposite sex who is a husband or wife.” In order for the Census Bureau to be consistent with this act and the data requirements of other federal agencies, same-sex “spouse” responses were invalidated.

2.      The second factor took into consideration that couples in long term same-sex relationships may consider themselves as “married partners” and thus respond as such on the census form.  In addition, at the time of writing the editing program for Census 2000, there were several challenges in the courts concerning the legality of same-sex marriages. Clearly, we could not ignore the fact that same-sex spouse responses were going to be recorded during Census 2000. In light of these social and legal aspects and the lack of a key variable in the statistical allocation routine (marital status) the assignment of same-sex “married” couples to the same-sex “unmarried partner” category was the procedure chosen for the editing process. We were adverse to a randomized allocation of these responses after people had clearly marked a close relationship preference on the census form.

As a result of these changes in the processing routine, estimates of same-sex unmarried partners are not comparable between the 1990 and 2000 census.