I can't give you references, although I have read research, some time ago. You can easily perform a search, but I bet they will request that you pay for the articles. If you look them up in a college library, one journal would be the Journal of Counseling, Journal of Counseling and Psychotherapy, and the Journal of Clinical and Counseling Psychology. Look here:
http://books.google.com/books/about/The_great_psychotherapy_debate.html?id=glGPRwSlgrsC
Usually such studies try to compare the effectiveness (number of people who are relieved of symptoms or how much they are relieved of symptoms over a period of time; often these people are followed some time later to see if it lasts) of different therapeutic techniques. Since only two (and now three) methods use a measurable way of gauging effectiveness, namely Cognitive Behavior Therapy (CBT), Behavior therapy, and Action Commitent Therapy (ACT, an outgrowth of CBT), these therapies are usually found to be more effective. Psychodynamic therapies, psychoanalysis, and Existential Therapy usually do not and cannot measure changes in symtoms. They are usually non-directive approaches and allow the patient to present his/her own solutions. That is why they usually take so long. Traditional CBT, ACT, and behavior therapy usually are very programmed and use a set number of sessions.
Another thing to consider is the following. An analogy to such statistical studies are studies that show the effectiveness of medication. According to most studies I have seen, Prozac is the most effective treatment for depression. Some people might wonder, why use anything else? Well, Prozac does not work for everyone, because people are not statistics. The same is true of therapy. Some people rebel against what they see as the regimentation of CBT.
I have seen a number of patients for one or two sessions because they said that they wanted to discuss their past; they told me that they had been in treatment for six years and needed to explore their past more. When I suggested that they might want to learn strategies to overcome their problems rather than rehashing their past, which has not helpsed them, they agreed, but never came back. I am willing to listen to the root of the problem, but then you have to resolve that issue, I believe. Just revealing it does not resolve it, as the old-style psychanalysis believed, at least that is my opinion. Some people need help to resolve it.
I hope that answered your question.