The subject of Jones and Yarhouse’s Ex-Gays?, whether or not there is evidence that those with homosexual orientation can change that orientation, is not an easy topic to discuss. But, I think we’ve seen that we can talk and learn from one another. The rationale of the study is the topic of chp 3.
Here are two paragraphs from the American Psychological Association website that J-Y publish:

Can Therapy Change Sexual Orientation?
No. Even though most homosexuals live successful, happy lives, some homosexual or bisexual people may seek to change their sexual orientation through therapy, sometimes pressured by the influence of family members or religious groups to try and do so. The reality is that homosexuality is not an illness. It does not require treatment and is not changeable.
However, not all gay, lesbian, and bisexual people who seek assistance from a mental health professional want to change their sexual orientation. Gay, lesbian, and bisexual people may seek psychological help with the coming out process or for strategies to deal with prejudice, but most go into therapy for the same reasons and life issues that bring straight people to mental health professionals.
What About So-Called “Conversion Therapies”?
Some therapists who undertake so-called conversion therapy report that they have been able to change their clients’ sexual orientation from homosexual to heterosexual. Close scrutiny of these reports however show several factors that cast doubt on their claims. For example, many of the claims come from organizations with an ideological perspective which condemns homosexuality. Furthermore, their claims are poorly documented. For example, treatment outcome is not followed and reported overtime as would be the standard to test the validity of any mental health intervention.
The American Psychological Association is concerned about such therapies and their potential harm to patients. In 1997, the Association’s Council of Representatives passed a resolution reaffirming psychology’s opposition to homophobia in treatment and spelling out a client’s right to unbiased treatment and self-determination. Any person who enters into therapy to deal with issues of sexual orientation has a right to expect that such therapy would take place in a professionally neutral environment absent of any social bias.

It is the “not changeable” that concerns Jones and Yarhouse.
This chp briefly tells the genesis of their own research, beginning with changes in the APA and then how Jones himself was not able to find grants for research into the question of whether or not orientation is immutable or changeable. Eventually Exodus International contacted Jones to see if funds were found if he would do the research.
Three studies since the 80s on change: MacIntosh surveyed therapists about their perception of their clients and changing orientation with about 23% of clients changing orientation; most of the therapists did not believe a patient “can and should” change; the problem here, of course, is that this is perception by therapists. NARTH studied “success stories” and Shidlo/Schroeder studied “failure stories.” None of these studies is empircally compelling, though none should be discounted either.
Three studies about religiously mediate change: the Pattison study, the Schaeffer study, and the Spitzer study each is reviewed — the results stated and the limitations of the studies clarified. Still, there are some results that can’t be denied: some do change their orientation.
They report and interact with Haldeman’s influential study that subjects “conversion” literature as either biased or inconclusive. They then survey recent literature on “immutability” — that homosexuality is unchangeable. Jones and Yarhouse say this: “to argue for the immutability of sexual orientation is ill-founded” (98).
But, their study is based on the hypothesis of the APA that change is impossible and they seek to test that hypothesis. Further, they will test the hypothesis that changing orientation is harmful.