A 2009 systematic review looking at individual surgical procedures found that "[t]he evidence concerning gender reassignment surgery in both MTF and FTM transsexism has several limitations in terms of: (a) lack of controlled studies, (b) evidence has not collected data prospectively, (c) high loss to follow up and (d) lack of validated assessment measures. Some satisfactory outcomes were reported, but the magnitude of benefit and harm for individual surgical procedures cannot be estimated accurately using the current available evidence."[12]
A 2010 meta-analysis of follow-up studies reported that "[v]ery low quality evidence suggests that sex reassignment that includes hormonal interventions in individuals with GID likely improves gender dysphoria, psychological functioning and comorbidities, sexual function and overall quality of life. MF transsexuals may have worse outcomes than FM individuals." Specifically, the study found that "Pooling across studies shows that after sex reassignment, 80% of individuals with GID reported significant improvement in gender dysphoria (95% CI = 68–89%; 8 studies; I2 = 82%); 78% reported significant improvement in psychological symptoms (95% CI = 56–94%; 7 studies; I2 = 86%); 80% reported significant improvement in quality of life (95% CI = 72–88%; 16 studies; I2 = 78%); and 72% reported significant improvement in sexual function (95% CI = 60–81%; 15 studies; I2 = 78%)."[13]
With regards to follow-up, Kaplan and Sadock's Comprehensive Textbook of Psychiatry states, "Clinicians are less likely to report poor outcomes in their patients, thus shifting the reporting bias to positive results. However, some successful patients who wish to blend into the community as men or women do not make themselves available for follow-up. Also, some patients who are not happy with their reassignment may be more known to clinicians as they continue clinical contact."[2]:2109
A recent Swedish study (2010) found that “almost all patients were satisfied with sex reassignment at 5 years, and 86% were assessed by clinicians at follow-up as stable or improved in global functioning”[14] A prospective study in the Netherlands that looked at the psychological and sexual functioning of 162 adult applicants of adult sex reassignment applicants before and after hormonal and surgical treatment found, "The vast majority functioned quite well psychologically, socially and sexually. Two non-homosexual male-to-female transsexuals expressed regrets." (The term "non-homosexual" in this context refers to persons who were attracted to persons of the sex that was opposite to their birth sex prior to surgery - that is, male-to-female transsexuals who were attracted to women and female-to-male transsexuals who were attracted to men.)[15]
A long-term follow-up study performed in Sweden over a long period of time (1973–2003) found that morbidity, suicidality, and mortality in post-operative transsexual persons were still significantly higher than in the general population, suggesting that sex reassignment therapy is not enough to treat gender dysphoria, highlighting the need for improved health care following sex reassignment surgery. The study, however, states that "no inferences can be drawn [from this study] as to the effectiveness of sex reassignment as a treatment for transsexualism," citing studies showing the effectiveness of sex reassignment therapy, though noting their poor quality. The authors noted that the results suggested that those who received sex reassignment surgery before 1989 had worse mortality, suicidality, and crime rates than those who received surgery on or after 1989: mortality, suicidality, and crime rates for the 1989-2003 cohort were not statistically significant compared to healthy controls (though psychiatric morbidity was); it is not clear if this is because these negative factors tended to increase a decade after surgery or because in the 1990s and later improved treatment and social attitudes may have led to better outcomes.[16]
The abstract of the American Psychiatric Association Task Force on GID's report from 2012 states, "The quality of evidence pertaining to most aspects of treatment in all subgroups was determined to be low; however, areas of broad clinical consensus were identified and were deemed sufficient to support recommendations for treatment in all subgroups."[3] The APA Task Force states, with regard to the quality of studies, "For some important aspects of transgender care, it would be impossible or unwise to engage in more robust study designs due to ethical concerns and lack of volunteer enrollment. For example, it would be extremely problematic to include a 'long-term placebo treated control group' in an RCT of hormone therapy efficacy among gender variant adults desiring to use hormonal treatments." [3]:22 The Royal College of Psychiatrists concurs with regards to SRS in trans women, stating, "There is no level 1 or 2 evidence (Oxford levels) supporting the use of feminising vaginoplasty in women but this is to be expected since a randomised controlled study for this scenario would be impossible to carry out."[7]
http://en.wikipedia.org/wiki/Sex_reassignment_therapy#References