For years atheists have been making a simplistic analysis that we can assume a causal inference bewteen the percentage of prisoners who are Christians and the effect of Christianity on behavior. The assumption is being a Chrsitains make you more likely to go to prison. The classic page on this is Holy smoke.org which I have discussed on Atheist Watch as pure propaganda. The page demonstrates a set of spurious data supposedly showing that there are many more times Chrsitains in prison than non Christians. I've raised questions about the validity of the data. Even an atheist site calls it a questionable source.
....This same site recoginizes the fact of the Pew study on Chaplins that there are atheists then thought prevoiusly:
Last week, the Pew Research Center’s Forum on Religion & Public Life released the results of a survey of professional prison chaplains across the United States. The results (PDF) offer some insight into the religious lives of prisoners. But keep in mind it’s not necessarily accurate — they’re asking chaplains across the country what they think the religious makeup of the prisoners is.While I laud his honestly in acknowledging that the percentage of atheists is higher than Swift's 2% (putting it up at 11%) he misses the real import of the Pew study (not to criticize an honest man). The real import is that it shows that prisons switch their faiths a lot. So there's no evidence that all of the Christians in prison at any given moment were Chrsitians when they went to prison. That means they can't argue Christianity is a moral failure. It's true that there are many nominal Chrsitains who mouth the words but don't have the experiences. It's only a correlation in the first place, there's no real way to make into a viable indictment of Christian life, but how what we know prisons are not even going in as Christians necessarily the data becomes totally useless.
Although chaplains, like all observers, undoubtedly bring their own perspectives and predilections to bear, they also occupy a valuable vantage point as correctional workers who have regular, often positive interactions with inmates and take a strong interest in the role of religion in inmates’ lives.(ibid)
....The Study is "Religion in Prisons: 50 state survey of prison chaplains," by the Pew Research  Of course the atheists have already begun the cry of "this is not accurate becuase they chaplains so they lie (see comment section of friendly atheist site), the Chaplins have access to prison stats which are not typically available to the pubic.
A majority of chaplains surveyed report that the prison where they work has a formal system in place both for documenting the religious affiliation of inmates (84%) and for documenting changes in religious affiliation (76%). However, such records typically are for in-house use only. As previously noted, official statistics on the religious affiliation of the state prison population generally are not publicly available. Thus, the Pew Forum survey provides a unique look —based on the chaplains’ own estimates — at the relative size and growth of religious groups behind bars.
The Chaplains show that switching groups religiously is quite common and that growing of both Islam and protestantism is due to largely to switching.
A majority of chaplains say that attempts by inmates to convert or proselytize other inmates are either very common (31%) or somewhat common (43%), while 26% say such attempts are not too or not at all common...Still, a majority of chaplains say that there is either “a lot” of religious switching (26%) or “some” switching among inmates (51%). About one-fifth (21%) say that switching occurs “not much” or not at all in the prisons where they work.
I'm sure the survey is not as unbiased or accurate as it could be. Yet there's just as much confusion about surveys asking prisoners directly for their affiliation. They still dont' include a place in the data for conversion history nor do they try to ascertain the person's affiliation before prison. The conclusion is corroborated by the book Religion, the Community, and Rehabilitation of Criminal offenders. "The most common reason for conversion in prison is seen as protection. So then it's not surprising that religion as a form of protection is closely connected with the deprivation of security." This is a study of original research. although they do point out that their research does not support the parole theory of insincere conversion. This applies to insincere this doesn't' mean that there isn't sincere conversion.
....As to the question about convesion for parole, while the O'Connor evidence doesn't agree two other studies show that this might be a factor. Two studies on race and religions show that religion could be a factor.
Parole board members (PBMs) decide whether to release inmates on parole. Decisions may be affected by in-group bias or stereotypes regarding religion and race. Two experiments investigated whether religious conversions/secular lifestyle changes and race affect mock PBMs' release decisions, emotions, and perceptions. Mock PBMs read a case file of an inmate who was eligible for parole and decided whether to grant parole. Study 1 manipulated whether the inmate had converted to Christianity or Islam, had a secular lifestyle change, or had no lifestyle change. Study 2 also varied race (African American or Caucasian). Race was not a significant factor, possibly because the manipulation was not strong enough to influence participants or because participants did not want to appear racist. Conversions to Islam and Christianity impacted the parole decision, and effects were mediated by believability of the conversion. Secular lifestyle changes affected release decisions and were mediated by perceptions of the inmate and beliefs about his likelihood of recidivism. Such inmates were the most likely to be released and were perceived most positively; their conversions were the most believable. Inmates who made no changes were perceived least positively, indicating that any lifestyle change is better than none. Importantly, no bias towards either religion (Islam, Christianity) was found. Furthermore, conversion type affected how scared PBMs were of the inmate, but this fear did not impact release decisions.
 Friendly Atheist URL: http://www.patheos.com/blogs/friendlyatheist/2012/03/29/what-percentage-of-prisoners-are-atheists-pew-forum-offers-an-answer/
 The Study is "Religion in Prisons: 50 state survey of prison chaplains," by the Pew Research, Form the Pew Forum on Religion and Public Life. URL:
Thomas P. O'Connor and Nathaniel J. Pallone, Religion, the Community, and Rehabilitation of Criminal offenders.Routlege, 2013, also published as Journal of Offended Rehabilitation vol. 35, numbers 3/4 2002.
Monica K Miller, Samuel C Lindsey, and Jennifer A Kaufman. Legal and Criminological Psychology: The religious conversion and race of a prisoner: Mock parole board members' decisions, perceptions, and emotions. (vol 18, issue 1) First published online 26 SEP 2012 URL: