Researchers in the US claim to have identified a correlation between the success of the 'Christian right' and the rise in the number of people who describe themselves as atheists or religiously unaffiliated.

The study by Paul A Djupe, Jacob R Neiheisel, and Kimberly H Conger entitled Are the Politics of the Christian Right Linked to State Rates of the Nonreligious? The Importance of Salient Controversy is published in Political Research Quarterly.

It refers to a longstanding argument that 'the Christian Right is the most visible manifestation of religion in the United States, and the extreme positions taken by the movement on abortion and especially gay rights made all religion inhospitable for liberals and moderates'. It says: 'Our findings suggest that Christian Right influence in state politics seems to negatively affect religion, such that religious attachments fade in the face of visible Christian Right policy victories.'

The rise of the 'nones', the study says, began in 1994, when the religious right began to become more politically significant. It uses information gathered from the Cooperative Congressional Election Study to produce a state-by-state graph of the rise in irreligion and charted this against 'registered lobbying groups associated with the Christian Right, the number of gay rights lobbies, the number of lobbying groups affiliated with the religious left', adding a marker for whether the state had ever enacted a ban on gay marriage.

The study says: 'First, when the Christian Right is seen as influential in a state (visibility) that has a same-sex marriage ban in place (salient conflict), the number of religious nones will rise. Second, when there is a joint presence of Christian Right and gay rights groups registered to lobby (another available measure of salient conflict), the number of religious nones will rise.' Furthermore, 'the religious tradition most closely identified with the Christian Right – evangelical Protestants – may have reduced growth rates in states where Christian Right activity was salient and controversial.'

In its conclusion, the study notes the risk of speaking out on controversial issues, saying: 'Doing so except when public opinion is essentially united will entail lost membership, declining rates of organizational engagement, and reduced support from outside the group by some. At times, this is the necessary price of principle, but the schedule of rates should be well understood.'

It also notes the 'irony' that while speaking out on right-wing causes is damaging to the evangelical cause, left-wing protests against segregation during the civil rights era led to many leaving churches then as well: 'And just as involvement in the controversies of the day ushered in a period of organizational decline in which parishioners deserted mainline Protestantism in droves, it appears as though the Christian Right is following a strikingly similar path.'