Penile plethysmography (PPG), or "phallometry", refers to measurement of bloodflow to the penis. The most commonly reported methods of conducting penile plethysmography involve the measurement of the circumference of the penis with a mercury-in-rubber or electromechanical strain gauge, or the volume of the penis with an airtight cylinder and inflatable cuff at the base of the penis. Corpus cavernosa nerve penile plethysmographs measure changes in response to inter-operative electric stimulation during surgery. The volumetric procedure was invented by Kurt Freund and is considered to be particularly sensitive at low arousal levels. The easier to use circumferential measures are more widely used, however, and more common in studies using erotic film stimuli.
For sexual offenders it is typically used to determine the level of sexual arousal as the subject is exposed to sexually suggestive content, such as pictures, movies or audio. Although there are individuals who have claimed that phallometry is not always appropriate for the evaluation of sexual preferences or treatment effects, large-scale meta-analytic review of the scientific reports demonstrated that phallometric response to stimuli depicting children is the single most accurate (with only 32% accuracy) method of identifying which sexual offenders will go on to commit new sexual crimes.
For prostatectomy nerve-sparing surgery, the surgeon applies a mild electrical stimulation near the cavernous nerves of penis to verify their locations and avoid operative trauma. Damage to these difficult to see nerves can cause erectile dysfunction outcomes. At the surgery's conclusion, the electrical stimulation penile plethysmograph result is a prognostic which helps to manage the erectile function outcomes earlier than the many months required for recovery.
There are two types of penile plethysmograph:
- Volumetric air chamber
- When this is placed over the subject's penis, as tumescence increases, the air displaced is measured.
- Circumferential transducer
- This uses a mercury-in-rubber or indium/gallium-in-rubber ring or electromechanical strain gauge and is placed around the shaft of the subject's penis to measure changes in circumference.
Significant suppliers of PPG machines include Behavioral Technology Inc. and Medical Monitoring Systems. The device is known to be used in Brazil, Britain, Canada, China, Czech Republic, Hong Kong, New Zealand, Norway, Slovak Republic, Spain, and the United States.
The surgical machine is supplied as CaverMap by Blue Torch Medical Technology, Inc.
The original volumetric was developed during the 1950s by Kurt Freund in then-Czechoslovakia. Freund later wrote, "In the early fifties homosexual interaction was still an indictable offense in Czechoslovakia. I was of course opposed to this measure, but I still thought, as did my colleagues at the psychiatric university hospital in Prague where I was working, that homosexuality was an experientially acquired neurosis" (p. 223) He then developed phallometry to replace psychoanalytic methods of assessment because "[P]sychoanalysis had turned out to be a failure, virtually unusable as an instrument for individual diagnosis or research....When phallometry began to look promising as a test of erotic sex and age preferences, we started using it mainly as a test of pedophilia, that is determining who has an erotic preference for children over adults" (p. 223-224).
In post-World-War-II Czechoslovakia, Freund was assigned by the communist government the task of identifying among military conscripts men who were falsely declaring themselves to be gay. "Freund (1957) developed the first device, which measured penile volume changes... to distinguish heterosexual and homosexual males for the Czechoslovakian army."  When he escaped Europe for Canada, Freund was able to pursue his research using phallometry for the assessment of sexual offenders. At that time, attempts to develop methods of changing homosexual men into heterosexual men were being made by many sexologists, including John Bancroft, Albert Ellis, and William Masters of the Masters and Johnson Institute. Because phallometry showed that such methods were failures, Freund was among the first sexologists to declare that such attempts were unethical.
Reliability and validity 
In 1994, the Diagnostic and Statistical Manual of Mental Disorders (Fourth Edition) of the American Psychiatric Association stated that penile plethysmography has been used in research settings to assess various paraphilias by measuring an individual's sexual arousal in response to visual and auditory stimuli. The reliability and validity of this procedure in clinical assessment have not been well established, and clinical experience suggests that subjects can simulate response by manipulating mental images."
In 1998, Hanson and Bussière published a comprehensive meta-analysis of 61 scientific reports on the prediction of sexual offenses spanning more than 40,000 individual cases. They ascertained that of all the methods attempted and reported, penile phethysmographic responses to imagery depicting children was the single most accurate predictor of future offenses. Another meta-analysis in 2005 of 73 studies repeated the finding that phallometric responses to children was a highly effective technique.
Erectile dysfunction 
The penile plethysmograph has value in screening organic versus psychogenic erectile dysfunction in urological polysomnography centres. Lack of sexual response during REM sleep may indicate that further evaluation by a urologist is required.
When applied during nerve-sparing surgery, electrical stimulation penile plethysmograph is an erectile dysfunction prognostic. The patient is provided with objective information on his specific outcome which aids in planning for further erectile function therapies.
Male homosexuality 
A phallometric study indicated that men who are more homophobic show greater penile arousal to stimuli depicting gay sex than do less homophobic men.
Pedophilia and hebephilia 
Studies examining the efficiency of using penile plethysmograph to distinguish between pedophilic men from non-pedophilic men show that a majority can be correctly assigned to the proper category. In one study, 21% of the subjects were excluded for various reasons, including "the subject's erotic age-preference was uncertain and his phallometrically diagnosed sex-preference was the same as his verbal claim" and attempts to influence the outcome of the test. In a second study, sensitivity of the method to distinguish between pedophilic men from non-pedophilic men was estimated between 29% and 61% depending on subgroup.
Legal admissibility 
In general, phallometric test results are employed as part of the sentencing and rehabilitation phase of forensic systems, but not for determining whether a specific defendant is guilty of any specific offense against any specific person.
United States 
Use as trial evidence 
In the United States, a scientific technique could not be used as evidence in court unless the technique was "generally accepted" as reliable in the relevant scientific community. This was known as the Frye standard, adopted in 1923. In 1993, the doctrine was rejected by the Supreme Court of the United States in favor of a more comprehensive "reliable foundation" test in Daubert v. Merrell Dow Pharmaceuticals. In the Daubert standard, the "generally accepted" test was no longer determinative. Several other factors could now be considered, including whether the technique had been published and peer reviewed. Myers notes, "Courts that have considered penile plethysmography generally rule that the technique is not sufficiently reliable for use in court." 
In United States v. Powers the court excluded the penile plethysmograph test because it failed to qualify under Daubert's scientific validity prong for two reasons: the scientific literature does not regard the test as a valid diagnostic tool, and "a vast majority of incest offenders who do not admit their guilt, such as Powers, show a normal reaction to the test. The Government argues that such false negatives render the test unreliable." 
According to Barker and Howell, penile plethysmography (PPG) does not meet the legal threshold for the guilt phase for the following reasons:
- No standardization
- Test results are not sufficiently accurate
- Results are subject to faking and voluntary control by test subjects
- High incidence of false negatives and false positives
- Results are open to interpretation
They concluded, "Until a way can be devised to detect and/or control false negatives and false positives, the validity of the test data will be questionable." Responding to Barker and Howell, Simon and Schouten noted, "Our own analysis suggests that the standardization and faking issues, as well as other problems not addressed in the Barker and Howell paper, warrant much more guarded conclusions about the use of the plethysmograph in legal and clinical settings."  Prentky noted "the increased likelihood in forensic settings that dissimulation may compromise the validity of the assessment."  Hall and Crowther noted penile plethysmography "may be even more problematic than other [methods] in assessing susceptibility of the test to faking." 
In State of North Carolina v. Spencer, the court reviewed the literature and case law and concluded that penile plethysmography was scientifically unreliable: "Despite the sophistication of the current equipment technology, a question remains whether the information emitted is a valid and reliable means of assessing sexual preference."
More recently, a substantial amount of research data has been gathered and reviewed, and significant steps have been taken toward standardization. According to Launay (1999), "[T]he validity of the technique for research and clinical assessment is now established;" it is only the use in guilt-determination proceedings that is inappropriate. Fedoroff and Moran called it an "experimental procedure" and noted, "Virtually every expert who has written about phallometry has cautioned that it is insufficiently sensitive or specific to be used to determine the guilt or innocence of a person accused of a sex crime."
Post-conviction use 
Phallometry is widely considered appropriate for treatment and supervision of convicted sex offenders: "Courts have permitted plethysmographic testing for monitoring compliance by convicted sex offenders with the conditions of their community placement as part of crime-related treatment for sexual deviancy." Its use for the treatment and management of sexual offenders is recommended by the Association for the Treatment of Sexual Abusers. Becker notes it "should never be used exclusively in forensic decision making." The sexual assault trial of basketball player Kobe Bryant in Colorado brought this device and its use to public attention before the case was dropped in 2004, because Colorado law would have required evaluation with this device following conviction. The United States Court of Appeals for the Ninth Circuit recently addressed the procedures required before a federal supervised release program could include penile plethysmograph testing. The device is routinely used at civil commitment facilities, but "some clinicians and offenders say it is easy, particularly in a laboratory, to stifle arousal and thus cheat on a plethysmograph test." This has been reported to occur in 16% of cases.
During the Catholic sex abuse cases, the reliability of the test was questioned by some officials in the Roman Catholic Archdiocese of Philadelphia. Later, these officials chose to seek therapy at an institution where the plethysmograph was not used.
Courts in Canada came to a similar conclusion as those in the United States. The Supreme Court of Canada adopted the Daubert doctrine in R. v . J.-L.J.  2 S.C.R. 600, which upheld a lower court's decision to exclude testimony by a psychiatrist who had administered several tests on the accused, including a penile plethysmograph:
A level of reliability that is quite useful in therapy because it yields some information about a course of treatment is not necessarily sufficiently reliable to be used in a court of law to identify or exclude the accused as a potential perpetrator of an offence. In fact, penile plethysmography has received a mixed reception in Quebec courts: Protection de la jeunesse – 539,  R.J.Q. 1144; R. c. Blondin,  Q.J. No. 3605 (QL) (S.C.); L. Morin and C. Boisclair in "La preuve d'abus sexuel: allégations, déclarations et l'évaluation d'expert" (1992), 23 R.D.U.S. 27. Efforts to use penile plethysmography in the United States as proof of disposition have largely been rejected: People v. John W., 185 Cal.App.3d 801 (1986); Gentry v. State, 443 S.E.2d 667 (Ga. Ct. App. 1994); United States v. Powers, 59 F.3d 1460 (4th Cir. 1995); State v. Spencer, 459 S.E.2d 812 (N.C. App. 1995); J. E. B. Myers et al., "Expert Testimony in Child Sexual Abuse Litigation" (1989), 68 Neb. L. Rev. 1, at pp. 134-35; J. G. Barker and R. J. Howell, "The Plethysmograph: A Review of Recent Literature" (1992), 20 Bull. Am. Acad. of Psychiatry & L. 13.—
As of 2010, all youth in sex offender treatment programs administered by the Youth Forensic Psychiatric Service of British Columbia were offered a voluntary penile plethysmograph test to predict whether they can properly control their deviant arousal, or whether they will require medication or other forms of treatment. According to sceptics, however, the test does not reliably predict recurrent violations.
Ethics and legality of use 
Robert Todd Carroll writes, "More objectionable than the questionable scientific validity of the device, however, are the moral and legal questions its use raises." Carroll and others cite the legality of the depictions of minors, as well as the constitutionality of requiring PPG for admission to jobs or the military, or in custody cases. In Harrington v. Almy the United States Court of Appeals for the First Circuit found that a PPG ordered to be administered by William O'Donohue as a precondition of employment was a violation of plaintiff's rights under the Fourteenth Amendment to the United States Constitution. In a 2009 report led by Robert Clift on use of the device on adolescent offenders, the authors acknowledge in their conclusions that PPG tests "are problematic ethically and should be used only after therapists have carefully weighed the benefits versus the negatives." The Minister of Children and Family Development closed the program examined in Clift's report in 2010 following complaints by civil rights groups. The principal manufacturer of the device stopped making them in the 1990s.
The EU's leading human rights agency, the Fundamental Rights Agency, has criticised the use of phallometric tests by the Czech Republic to determine whether asylum seekers presenting themselves as homosexual were in fact gay. According to the Agency, the Czech Republic was in 2010 the only EU country to employ a sexual arousal test, which the Agency said could violate the European Convention on Human Rights. In 2011 the EU commission issued a statement calling the Czech practice illegal, saying "The practice of phallometric tests constitutes a strong interference with the person's private life and human dignity. This kind of degrading treatment should not be accepted in the European Union, nor elsewhere." 
See also 
- Simon, W. T., & Schouten, P. G. (1992). The plethysmograph reconsidered: Comments on Barker and Howell. Bulletin of the American Academy of Psychiatry and the Law, 20, 13-25.
- Hanson, R. K., & Bussière, M. T. (1998). Predicting relapse: A meta-analysis of sexual offender recidivism studies. Journal of Consulting and Clinical Psychology, 66, 348–362.
- Klotz L, Heaton J, Jewett M, et al (November 2000). "A randomized phase 3 study of intraoperative cavernosa nerve stimulation with penile tumescence monitoring to improve nerve sparing during radical prostatectomy". J. Urol. 164 (5): 1573–8. doi:10.1016/S0022-5347(05)67031-0. PMID 11025707.
- Howes, R. J. (1995). A survey of plethysmographic assessment in North America. Sexual Abuse: A Journal of Research and Treatment, 7, 9-24.
- Kuban M, Barbaree HE, Blanchard R (August 1999). "A comparison of volume and circumference phallometry: response magnitude and method agreement". Arch Sex Behav 28 (4): 345–59. doi:10.1023/A:1018700813140. PMID 10553495.
- Freund, K. (1991). Reflections on the development of the phallometric method of assessing sexual preference. Annals of Sex Research, 4, 221–228. doi:10.1007/BF00850054
- Wilson, R. J., & Mathon, H. F. (2006, fall). Remembering Kurt Freund (1914-1996). ATSA Forum. Beaverton, OR: Association for the Treatment of Sexual Abusers.
- W O'Donohue, E Letourneau. The psychometric properties of the penile tumescence assessment of child molesters. Journal of Psychopathology and Behavioral Assessment, 1992
- Bancroft J (December 1969). "Aversion therapy of homosexuality. A pilot study of 10 cases". Br J Psychiatry 115 (529): 1417–31. doi:10.1192/bjp.115.529.1417. PMID 5358532.
- Ellis, A. (1956). The effectiveness of psychotherapy with individuals who have severe homosexual problems. Journal of Consulting Psychology, 20, 191-195.
- Schwartz MF, Masters WH (February 1984). "The Masters and Johnson treatment program for dissatisfied homosexual men". Am J Psychiatry 141 (2): 173–81. PMID 6691475.
- DSM-IV, p. 524.
- Hanson, R. K., & Morton-Bourgon, K. E. (2005). The characteristics of persistent sexual offenders: A meta-analysis of recidivism studies. Journal of Consulting and Clinical Psychology, 73, 1154-1163.
- Marshall P, Surridge D, Delva N (February 1981). "The role of nocturnal penile tumescence in differentiating between organic and psychogenic impotence: the first stage of validation". Arch Sex Behav 10 (1): 1–10. doi:10.1007/BF01542669. PMID 7212992.
- Klotz L (January 2004). "Cavernosal nerve mapping: current data and applications". BJU Int. 93 (1): 9–13. doi:10.1111/j.1464-410X.2004.04546.x. PMID 14678359.
- Adams, H. E., Motsinger, P., McAnulty, R. D., & Moore, A. L. (1992). Voluntary control of penile tumescence among homosexual and heterosexual subjects. Archives of Sexual Behavior, 21, 17–31. doi:10.1007/BF01542714
- FREUND K (May 1963). "A LABORATORY METHOD FOR DIAGNOSING PREDOMINANCE OF HOMO- OR HETERO-EROTIC INTEREST IN MALE". Behav Res Ther 1: 85–93. doi:10.1016/0005-7967(63)90012-3. PMID 14156719.
- Freund K (August 1967). "Diagnosing homo- or heterosexuality and erotic age-preference by means of a psychophysiological test". Behav Res Ther 5 (3): 209–28. doi:10.1016/0005-7967(67)90036-8. PMID 6063529.
- Adams HE, Wright LW, Lohr BA (August 1996). "Is homophobia associated with homosexual arousal?". J Abnorm Psychol 105 (3): 440–5. doi:10.1037/0021-843X.105.3.440. PMID 8772014..
- Blanchard R, Klassen P, Dickey R, Kuban ME, Blak T (March 2001). "Sensitivity and specificity of the phallometric test for pedophilia in nonadmitting sex offenders". Psychol Assess 13 (1): 118–26. doi:10.1037/1040-3518.104.22.168. PMID 11281033.
- Freund K, Blanchard R (February 1989). "Phallometric diagnosis of pedophilia". J Consult Clin Psychol 57 (1): 100–5. doi:10.1037/0022-006X.57.1.100. PMID 2925958.
- Murphy, W. & Barbaree, H. E. (1994). Assessments of sexual offender by measures of erectile response: Psychometric properties and decision making. Brandon, VT: Safer Society Press.
- Buhrich, N., & McConaghy, N. (1977). The discrete syndromes of transvestism and transsexualism. Archives of Sexual Behavior, 6, 483–495.
- Freund, K., Seto, M. C., & Kuban, M. (1996). Two types of fetishism. Behaviour Research and Therapy, 34, 687–694.
- Seto, M. C., & Kuban, M. (1996). Criterion-related validity of a phallometric test for paraphilic rape and sadism. Behaviour Research and Therapy, 34, 175–183.
- Myers JEB (2005). Myers on Evidence in Child, Domestic, and Elder Abuse Cases. Aspen Publishers Online ISBN 0-7355-5668-7
- United States v. Powers, 59 F.3d 1460 (4th Cir. 1995)
- Barker and Howell, The Plethysmograph: A Review of Recent Literature, 20 Bull. Am. Acad. of Psychiatry and Law 13 (1992)
- Prentky RA, Knight RA, Lee AFS (1997) Risk factors associated with recidivism among extrafamilial child molesters. Journal of Consulting and Clinical Psychology.
- Hall GCN, Crowther JH (1991). Psychologists' involvement in cases of child maltreatment: additional limits of assessment methods. American Psychologist Jan Vol 46(1) 79-80
- North Carolina v. Spencer, 459 S.E.2d 812, 815 (N.C. Ct. App. 1995),
- Launay, G. (1999). "The phallometric assessment of sex offenders: an update". Criminal Behaviour and Mental Health 9 (3): 254–274. doi:10.1002/cbm.317.
- Fedoroff, JP; Moran, B (1997). "Myths and Misconceptions about Sex Offenders". The Canadian Journal of Human Sexuality 6: 1997.
- Sachsenmaier, S. J., & Peters, J. M. (2002). Sexual offender risk assessment methods and admissibility as expert witness evidence. In J. M. Peters (Ed.), Assessment and management of sex offenders: What prosecutors need to know. Washington, DC: United States Department of Justice, Child Exploitation and Obscenity Section
- Association for the Treatment of Sexual Abusers. (2004). ATSA Practice Standards and Guidelines for the evaluation, treatment and management of adult male sexual abusers. Beaverton, OR: Author.
- Becker JD, Murphy WD (1998). What we know and do not know about assessing and treating sex offenders. Psychology, Public Policy, and Law. Volume:4 Issue:1/2 Dated:March/June 1998 Pages:116 to 137
- Mark Shaw for USATODAY- Bryant's off-court issues may aid prosecution
- United States v. Weber, 2006 U.S. App. LEXIS 15111 (9th Cir. 2006).
- Goodnough A, Davey M (March 6, 2007). For Sex Offenders, a Dispute Over Therapy's Benefits. New York Times
- Blanchard, R., Klassen, P., Dickey, R., Kuban, M. E., & Blak, T. (2001). Sensitivity and specificity of the phallometric test for pedophilia in nonadmitting sex offenders. Psychological Assessment, 13, 118-126.
- Court of Common Pleas, First Judicial District of PA, County Investigating Grand Jury, 9-17-2003
- R. v . J.-L.J.,  2 S.C.R. 600
- Adrian MacNair: B.C. government rethinks penis-arousal tests (National Post, July 29, 2010)
- Carroll, Robert Todd (2003). Penile plethysmograph (PPG). The skeptic's dictionary: a collection of strange beliefs, amusing deceptions, and dangerous delusions, pp. 278-281. John Wiley and Sons, ISBN 978-0-471-27242-7
- Harrington v. Almy, 977 F.2d 37 (1st Cir.1992)
- Ford, Royal (June 19, 1993). Maine officer who refused sex response test wins suit. Boston Globe
- Clift, JRW; Rajlic, G; Gretton, H (2009). "Discriminative and Predictive Validity of the Penile Plethysmograph in Adolescent Sex Offenders". Sexual Abuse 21 (3): 335–362. doi:10.1177/1079063209338491. PMID 19587382.
- Bula, Frances (July 27, 2010). B.C. rights group complains about testing of young sex offenders. The Globe and Mail
- Staff report (August 8, 2010). B.C. used penile teen sex test for decades. CBC News
- Wintonyk, Darcy (July 29, 2010). B.C. permanently halts sexual arousal testing. CTV News
- Hyde, Alan (1997). The legal penis. Bodies of Law, pp. 173 ff. Princeton University Press, ISBN 978-0-691-01228-5
- Czech gay asylum 'phallometric test' criticised by EU (BBC, December 8, 2010)
- Czech sexuality tests not legal, EU commission says (EUobserver, 17.05.2011)
- Legal Definition of Penile Plethysmograph
- Online version of penile plethysmography entry in Skeptic's Dictionary via Robert Todd Carroll
- British Psychological Society's Guidelines for PPG
- Phallometry in Research and Clinical Diagnosis by Dr. Ray Blanchard