New research has finally found a link between the length of a relationship and the decline in a woman's desire for sex.
According to LiveScience, the findings were based on a survey of 170 undergraduates who'd been in relationships that had lasted from one month to nine years. The subjects reported on their levels of "relationship satisfaction, sexual satisfaction and sexual desire," and scored desire using a model called the Female Sexual Function Index (ranges from 1.2 to 6.0).
Participants reported that they were generally satisfied with their sex lives and their relationships. However, the study did show that while male desire held steady over the course of a relationship, that female level of desire would steadily drop based on how long they'd been in the relationship:
Specifically, for each additional month women in this study were in a relationship with their partner, their sexual desire decreased by 0.02 on the Female Sexual Function Index.
Despite being a small study, these results could help researchers understand why women who seek sex therapy complain of low desire more than any other problem.