by David Kim

The Supreme Court of South Carolina unanimously held that results of the penile plethysmography test (“PPG”) are inadmissible in judicial proceedings “unless and until the science underlying the PPG becomes more fully developed and uniform,” reasoning that the pervasive lack of standardization in administering and scoring the test prevents any finding of reliability under Rule 702 of the South Carolina Rules of Evidence (“SCRE”) and State v. Council, 515 S.E.2d 508 (S.C. 1999). The Court further ruled that the PPG results admitted at Andy Hyman’s sexually violent predator (“SVP”) commitment trial were independently inadmissible under Rule 403 and that their admission was prejudicial, entitling Hyman to a new commitment proceeding.

Background

The PPG attempts to objectively quantify male sexual arousal. After a man sexually stimulates himself and places a mercury strain gauge around his penis, an observer spends several hours recording changes in penile circumference as erotic and non-erotic visual and auditory stimuli are presented. The test is intensely controversial within the scientific community. No universal standards govern its administration or the interpretation of its results, false positives and false negatives occur at a rate of approximately 20 percent, and the test cannot account for numerous variables affecting erectile responses, including the recency of an offender’s last orgasm, intoxication, fatigue, cardiovascular health, medications, age, intelligence, seasonal testosterone fluctuations, and the gender of the administering clinician.

In 1997, Hyman pleaded guilty to second degree criminal sexual conduct with a minor (“CSCM”) and lewd act on a minor, and he completed supervised release in 2003. He pleaded guilty to third degree CSCM in 2016 and received a 10-year prison sentence. Before his release, the State initiated civil commitment proceedings under the SVP Act, and the South Carolina Office of Mental Health (“OMH”) performed the statutorily required pre-commitment evaluation through its chief psychologist, Dr. Marie Gehle. See S.C. Code Ann. § 44-48-80(D). Although she diagnosed Hyman with pedophilic disorder, Gehle concluded he was not an SVP because he did not pose the heightened risk of reoffending the Act requires. Consistent with OMH practice, she performed no PPG. Dissatisfied, the State obtained a second opinion from Dr. Emily Gottfried, director of the Sexual Behavior Clinic and Lab at the Medical University of South Carolina (“MUSC”). Gottfried administered a PPG pursuant to her standard practice, reached the same diagnosis, and concluded Hyman did qualify as an SVP.

Hyman moved in limine to exclude the PPG results, arguing the test lacked standardization and peer-reviewed validation and that the jury would seize upon the results to the exclusion of all other evidence. Following proffered testimony from both experts, the trial court denied the motion. At trial, Gottfried described the PPG to the jury as “an objective physiological measure of male sexual arousal,” “the gold standard of looking at males[’] sexual arousal,” and a “strong predictor or risk factor for future sexual offending,” even though both experts agreed Hyman’s actuarial scores placed him “squarely within the average rate of recidivism” for sex offenders. During closing argument, the State told the jury the PPG results alone justified commitment. The jury deliberated 22 minutes before finding Hyman an SVP. The court of appeals reversed, holding the trial court abused its discretion in finding the PPG reliable, and the Supreme Court granted the State’s petition for a writ of certiorari.

Analysis

The Court reviewed the evidentiary ruling under a deferential standard, explaining that reversal requires a manifest abuse of discretion accompanied by probable prejudice. State v. Commander, 721 S.E.2d 413 (S.C. 2011). An abuse of discretion exists when the trial court’s conclusions lack evidentiary support or rest on an error of law. State v. Pagan, 631 S.E.2d 262 (S.C. 2006).

Under Rule 702, a trial judge admitting scientific evidence must find that the evidence will assist the trier of fact, that the expert is qualified, and that the underlying science is reliable. The Court stated that Council instructs courts to assess reliability by examining “(1) the publications and peer review of the technique; (2) prior application of the method to the type of evidence involved in the case; (3) the quality control procedures used to ensure reliability; and (4) the consistency of the method with recognized scientific laws and procedures.” Even reliable evidence remains subject to exclusion under Rule 403 if its probative value is substantially outweighed by the danger of unfair prejudice.

Three of the four Council factors will never favor reliability so long as the PPG exists in its current form, the Court explained. On publications and peer review, the scientific community is polarized, and even the PPG’s proponents concede the test is not standardized. The DSM-5, which the State invoked repeatedly, acknowledges that “the sensitivity and specificity of diagnosis may vary from one [laboratory] to another.” Published studies offer limited help because authors typically fail to disclose which stimulus sets generated their data, making replication and cross-study comparison nearly impossible. Prior use of the PPG fared no better. OMH, the designated court-appointed evaluator in every SVP proceeding in the state, refuses to employ the test because of its reliability and validity concerns, meaning every commitment case already includes one expert who assesses reoffense risk without it.

MUSC’s quality control procedures, the third factor, drew measured praise. Gottfried described controlled room conditions, repeated gauge calibration, and countermeasures against feigned or suppressed arousal. However, nothing in the record showed those practices are standard across other laboratories, and no research proves the countermeasures work. The Court deemed the factor neutral at best. See State v. Chavis, 771 S.E.2d 336 (S.C. 2015) (procedural consistency alone does not establish reliability).

The fourth factor exposed what the Court called the PPG’s “complete absence of reliability.” Laboratories may vary the test in at least 17 respects, including stimulus type and data sampling rate. The Court singled out two variables. Each laboratory sets its own “cut score” marking when increased penile circumference signifies arousal; although the literature identifies 2.5 millimeters as the threshold, MUSC arbitrarily doubled it to 5 millimeters without any supporting study. Each laboratory also selects its own stimulus sets, and MUSC runs two complete sets back-to-back, a protracted format the scientific community has never studied and one that undermines confidence in either set standing alone, according to the Court. Because an examinee could plausibly receive different results at different laboratories based purely on unregulated protocol choices, the Court concluded that the PPG was wholly inconsistent with recognized scientific practices and held its results inadmissible under Rule 702 and Council. [Editor’s Note: The holding follows the overwhelming majority rule, catalogued in an appendix to the opinion, and the Court distinguished the three contrary jurisdictions. Washington admits PPG results by statute, while Illinois and Florida apply the Frye general acceptance standard, which South Carolina never adopted.]

The Court held the results inadmissible under Rule 403 as well. By converting a private physiological reaction into numerical data, the PPG cloaks “an inherently subjective experience” in an aura of scientific objectivity that ordinary testimony lacks, the Court stated. That veneer makes the results difficult for a factfinder to discount and diminishes the jury’s role in weighing competing experts’ credibility. Given the test’s dubious reliability, the Court concluded the results naturally tend to confuse and mislead the jury such that any probative value of the PPG is “substantially outweighed by the danger of unfair prejudice.”

The Court noted that reversal requires error plus prejudice, In re Care & Treatment of Gonzalez, 763 S.E.2d 210 (S.C. 2014), and an error is harmless only when it could not reasonably have affected the result. State v. Byers, 710 S.E.2d 55 (S.C. 2011). Responding to Gottfried’s “gold standard” characterizations, the Court declared, “It is none of those things.” The State relied on the PPG at every stage, resisting a directed verdict and urging commitment in closing almost exclusively on its results, while both experts placed Hyman at only average recidivism risk. A 22-minute deliberation confirmed the prejudice, the Court observed.

Conclusion

Accordingly, the Court affirmed the court of appeals’ judgment reversing the commitment order and remanded for a new SVP commitment trial. See: In re Care & Treatment of Hyman, 2026 S.C. LEXIS 78 (2026).  

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