As a follow-up to last night’s post, I pulled the following article from ResearchGate. It discusses penile plethysmography and how it helps identify deviancy in sex offenders:
Standardization of Penile Plethysmography Testing in Assessment of Problematic Sexual Interests
Lisa Murphy, MCA,* Rebekah Ranger, BA, BSocSc,*†J. Paul Fedoroff, MD,*‡ Hannah Stewart, BA, BSc (in prog),*†R. Gregg Dwyer, MD, EdD,§and William Burke, PhD§
*Sexual Behaviours Clinic, Integrated Forensic Program, The Royal, Ottawa, ON, Canada; †Forensic Research Unit, University of Ottawa Institute of Mental Health Research, Ottawa, ON, Canada; ‡Department of Psychiatry, University of Ottawa, Ottawa, ON, Canada; §Sexual Behaviors Clinic and Lab, Community and Public Safety Psychiatry Division, Department of Psychiatry and Behavioral Sciences, Medical University of South Carolina, Charleston, SC, USA
DOI: 10.1111/jsm.12979
ABSTRACT
Penile plethysmography (PPG) is an objective measure of sexual arousal for men, commonly used to assess sexual arousal to both abnormal (i.e., paraphilic) and normal stimuli. While PPG has become a standard measure in the assessment and treatment of male sex offenders and men with paraphilic interests in both Canada and the United States, there is a lack of standardization of stimulus sets and interpretation of results between sites. The current article critically reviews the current state of the art while highlighting clinical and research efforts that may be undertaken in an attempt to reduce issues arising from lack of standardization across sites. Types and themes of stimulus sets, assessment apparatuses, laboratory preparation, and testing procedures are discussed. The continued development of standardized testing protocol and procedures across multiple international sites continues to be encouraged to promote unified PPG administration and interpretation, thus further enhancing the practical utility of the measurements and decreasing inter-rater discrepancies and error. Murphy L, Ranger R, Fedoroff JP, Stewart H, Dwyer RG, and Burke W. Standardization of penile plethysmography testing in assessment of problematic sexual interests. J Sex Med **;**:**–**.
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Penile tumescence, as measured by the penile plethysmograph, is a widely recognized means of measuring male sexual arousal to given stimuli. The use of penile plethysmography (PPG) has become a standard objective measure of arousal and is considered by some researchers and clinicians to be essential in the assessment and treatment of male sex offenders and men with paraphilic interests [1–8]. In the past, PPG has also been used to assess differences in penile responses observed from effects of medication [9] and as a result of biologic factors effecting erectile responses in nocturnal penile tumescence in the process of aging [10]. This article intends to focus solely on the standardization of PPG procedures when used in contexts to assess paraphilic and problematic sexual interests and arousal. A typical PPG assessment includes the presentation of sexual and neutral nonsexual stimuli while the subject wears a gauge that records electronic measurements of fluctuations in penile blood flow. The degree of arousal is measured by increase in penile circumference after the presentation of a given stimulus. Sexual response patterns can be compared with determine sexual interest [2].
Wide variation exists concerning stimuli types, assessment protocols and means of analyzing and interpreting phallometric results in forensic laboratories across North America [7]. Concerns regarding the lack of standardization in phallometry across sites have been discussed since its creation; however, little improvement has been made [2–4,6]. There are challenges in the implementation of standardization within jurisdictions and between countries. For example, forensic assessment laboratories in Canada typically rely on a combination of audio and visual stimuli; the visual stimuli often depicting nude images of children, as nude pictures of children and adolescents are permitted for clinical purposes. However, despite the clinical utility of such materials, they are prohibited in the United States [2,7]. Even within the same country, there is significant variation in the approaches utilized between laboratories.
While initially developed by Kurt Freund in the Czechoslovakia in the 1950s, PPG is not utilized as widely and frequently on the international scale as it is in North America. In a legal evaluation of PPG in the context of the Convention of Human Rights conducted by the European Court of Human Rights, the court reported that equipment and materials for PPG was available in seven of 25 establishments providing sex offender treatment in England and Wales. Of these seven, only three agencies conducted PPG regularly [11]. Gazan [11] reports the use of PPG in Belgium, but highlights the very limited use of this measure in other European countries.
This article identifies empiric technical data from peer-reviewed journal literature and academic books to provide a technical review of the current state of the art and makes recommendations for future research.
Assessment Stimulus
The types of PPG stimuli sets used to assess sexual arousal tend to be visual, auditory, or both. They are often presented in the form of still slides, videos, and audio recordings that are projected onto a large screen or wall for viewing. In the United States, it is illegal to possess photographs of nude persons under the age of 18, even for clinical, legal, or research purposes [2,7,12,13]. This is because the use of a photograph depicting a nude child defined as illegal in any case where the stimuli are intended to be used to elicit a sexual arousal response, falling under the legal definition of lascivious exhibition of the genital region [12,13]. As a result, all the stimuli sets in the United States are strictly audio or a combination of audio with nonnude and/or nude images of adults and nonnude images of children and teenagers under age 18.
In Canada, nude images with models of all ages are permitted for clinical assessment and are used routinely for research purposes. This exception arises from the “public good” statutory defense defined in s.163.1(6) of the Criminal Code of Canada, 1985. The defense described in this section circumvents criminal conviction in cases where the otherwise illegal pornographic material depicting children serves a “legitimate purpose related to the administration of justice or to science, medicine . . .” and “does not pose a risk of undue harm to persons under the age of 18 years” [14]. The audio depictions in both the United States and Canada have historically used adult male voices speaking in a monotone voice to describe both legal and illegal sexual scenarios [2]. However, even when different labs use the same types of materials, the content of the stimuli may differ between labs.
There is evidence that videotapes and auditory stimuli of preferred sexual scenarios are more effective than still slides in eliciting both subjective reports of sexual arousal based on self-report and measured changes in penile tumescence in men with paraphilic and nonparaphilic interests [2,8]. Some researchers have wondered if videotape stimuli may be too effective in evoking sexual stimulation, which may consequentially reduce discrimination between different categories of stimuli [15]. The authors of this article believe that this concern is unfounded as long as equivalent quality videos depicting other sexual scenario are presented. In these cases, data across different sexual scenarios can then be compared. In a sense, the person being tested becomes his own control.
While videotape scenarios provide an excellent test for sexual arousal, there are obvious ethical concerns about presenting videotapes of criminal sexual scenarios [16]. A paradoxical problem of videotape scenarios is that they may present too much information, given their explicit nature. Some men with paraphilic disorders tend to be highly specific in what they find arousing. Therefore, an audiotape in which the appearance of the person is left to the imagination of the individual being tested may be more effective at eliciting arousal than videotapes.
According to Lalumière and Harris [1], sexual preference for age and gender is most effectively discriminated using visual stimuli, while sexual arousal because of coercion is most effectively measured by presenting auditory stimuli [17]. Gaither and Plaud’s study found that sexual arousal was greater when audio stimuli accompanied video depictions of sexual behavior [18]. Looman and Marshall’s study comparing rapists to child molesters found that audiotapes describing sexual violence against children discriminated between rapists and child molesters [19]. This also held true for visual stimuli consisting of pictures of naked adult, pubescent, and prepubescent models. Responses were also found to vary based on the quality of the stimuli. For still slides, this included clarity and brightness, while for audio this included loudness and pitch [20,21].
Chaplin et al. found that greater differentiation between groups was achieved when victim trauma was included in the stimuli [22]. Specifically, they used audio voices that were age and gender congruent with the associated scenario and spoken from the victim’s perspective. For female children, an adult female’s voice was modified electronically to sound like a child, and age-congruent language was used. The Chaplin study has not been replicated to date.
Although not proven, it is reasonable to assume that the more realistic stimuli depictions are the more effective they will be in eliciting sexual responses similar to what can be elicited in real-life situations. Anecdotal reports from offenders raised the question of whether the use of child voices in PPG stimuli would increase the diagnostic discrimination of the stimuli. The authors of this article are currently conducting a study on the discriminant validity of first person monotone narrative stimuli and “real child voice” (RCV) stimuli in a group of men diagnosed with pedophilia and healthy controls.
The RCV stimulus set was conceived and then co-created by one of this article’s authors (W.B.) and then its use refined by two co-authors of this article (W.B. & G.D.), who at the time were both faculty at the Sexual Behaviors Evaluation, Research and Treatment Clinic and Laboratory at the University of South Carolina School of Medicine. The stimulus set includes male and female voices of all age ranges and incorporates adult–child interactions. Adult and child actors were hired to read nonsexual scripts in a recording studio. The parents of the child actors were fully informed, signed written consent forms and were present in the recording studio with their child while the audio-recording was being made. The scenarios were then digitally spliced and made into sexual scenarios, complete with professionally produced sound effects. The parents were not permitted to hear the final product. Digital photos of clothed models were used to pair with the age-congruent auditory stories and are presented before and after the RCV audio is played. The RCV stimulus set varies in ages from infants to adulthood, and includes mutually consenting, physically coercive or nonsexually violent scenarios.
More recently the use of virtually created mobile avatars has been explored as a stimuli option for PPG [23–26]. This approach helps to circumvent ethical concerns raised regarding the use of nude images of real children to assess deviant sexual interests [16]. The use of virtual test stimuli and PPG has been studied in order to better identify sexual orientation and age preference in men diagnosed with pedophilia [18,19]. Renaud and colleagues used a combination of viewing time and PPG. Results indicated that men diagnosed with pedophilia were significantly more likely to have a greater sexual response to nude child avatars than the controls. Participants also differed significantly on their viewing time of erogenous zones of the child avatar [24]. Currently, research is underway by the authors of this article that looks at the discriminate validity of mobile avatars and nude slides in a group of men diagnosed with pedophilia and healthy controls assessed with PPG.
Assessment Devices
Two categories of devices have traditionally been available for PPG, each with their own strengths and weaknesses. Volumetric assessment is conducted by fitting and sealing a tube device over the length of the penis to measure the displacement of air as an erection occurs, thereby measuring changes in both length and diameter [2,27,28]. This technique allows a shorter duration of stimulus exposure (approximately 30 seconds in duration), thus reducing time for the male to potentially distort his responses. This technique is acclaimed for obtaining highly accurate measurements, given its ability to detect small changes in erectile development [29–31]. Despite these strengths, drawbacks include a need for extensive technician training, the fitting of the apparatus needing to be done by the technician, and technical difficulties of administration [31–35]. Therefore, the use of circumferential assessment techniques is much more commonly utilized.
Circumferential assessments measure dynamic changes in penile diameter because of blood flow, by placing circumferential gauges halfway up the shaft of the penis [35]. Barlow gauges are flexible metal gauges, curved into an open circle, which expand as arousal increases. Barlow gauges are reliable and durable apparatuses [3,8,36]. These gauges may be most ideal for labs that do not frequently perform phallometric testing, as with proper care they can be stored and reused for longer periods than other circumferential assessment apparatuses [3]. Unfortunately, Barlow gauges have been observed to displace upon detumescence and subsequently may roll off of the flaccid penis. They also tend to be quite expensive to replace if damaged. These shortcomings have resulted in the use of an alternative gauge [3,37].
An alternate way to measure changes in penile circumference uses a circular strain gauge; thin rubber tubes filled with either mercury or indium-gallium to measure changes in electric resistance [33,37]. Although less durable than Barlow gauges, with a life of only a few months, strain gauges are less expensive. Research has shown that both types of circumferential gauges produce approximately equivalent results [3,37,38]. There is also a one-time use disposable version, thus eliminating the need for sterilization among subjects, which is also less expense if accidently (or purposely) damaged by a subject. Other studies have noted that metal band transducers may yield slightly less linear results compared with indium-gallium transducers [39]. One consideration to note when measuring penile circumference is that the circumference may decrease while the length of the penis increases during the initial stages of arousal [15,18,39,40]. Thus, the penis must be allowed time to increase both in length and in circumference before accurate measurement of maximal change in penile circumference may be obtained. Subsequently, longer administration time is required (approximately 2–4 minutes) as compared with the Barlow gauges [9].
Testing Protocol
In order to have proper standardization, it is important to have detailed instructions about the protocol. Prior to test commencement, the subject should be given instructions about the test procedures, particularly emphasizing that the subject is free to respond naturally to the presented stimuli and to avoid attempting to alter their responses [3,5].
A statement of informed consent should be signed and the subjects should be informed that they can revoke their consent and stop the test at any time. During the test, the subject sits in a secluded room by themselves in a recliner chair. Prior to beginning the assessment, the penile gauge is calibrated in accordance with the technical requirements of the test apparatus. The subject is given instructions on how to place an elastic band sensor around their penis to measure changes in penile circumference to stimuli. They are also asked to rate their level of sexual arousal to each scenario on a 5- or 10-point scale. A computer in the next room, where the assessment administrator sits, records change in penile circumference in response to the individual’s sexual arousal to the stimulus set and their self-ratings of the stimuli. In the labs of the authors of this article, testing is always followed by a debriefing session in which the results of the testing are reviewed.
Laboratory Rooms
Phallometric laboratories commonly consist of two rooms; one of the rooms is used for the testing and the other is used for the technician to administer and monitor the recordings. Equipment should be connected through a wall-mounted interface to permit wires to be connected through rooms. Along with a recliner chair, the testing room should also have an operator call button so the subject and administrator can communicate if needed. In addition, each testing room should have a screen or wall for presenting visual (slide and video) stimuli, and either headphones or speakers for presentation of audio stimuli [8]. The room should be of a comfortable temperature with appropriate lighting and dimming options. The technician’s room should contain a sink and a penile device sterilization station, computer to record measurements from the penile transducer, and an intercom to communicate with the subject [8]. If only disposable strain gauges are used, then the sterilization station is not required and at some sites such a station is in a separate space than the electronic components of the control room to avoid potential electric hazards if insufficient space for adequate separation.
Some laboratory procedures also include a video camera to monitor the upper body including the face, chest and arms in order to record and monitor attention to visual stimulus and body movements. The groin area of the subject remains covered by a drape and is not exposed during the assessment. In contrast, some labs use only auditory methods for communication between the technician and subjects [5,8].
Analysis and Interpretation of Results
Changes in penile circumference (blood flow) can be presented as changes in (raw scores) volume or voltage. Raw scores are transformed into either percentage of full erection or standardized changes in circumference (millimeters of change) using z-scores. Such transformations reduce variability and permit within and between subject comparisons. Differences in penis size and sexual responsivity are also areas of concern which may be addressed by these transformations [3].
Given the potential for error, there has been a shift toward the use of z-scores based on circumference change. The change in millimeters (mm) is calculated by subtracting the circumference of the penis at flaccid (baseline level) from the circumference of the penis at the highest level of arousal obtained during the presentation of the stimuli (peak level). This method of analysis produces a single scale of measurement that can be used to compare individual responses to all of the presented scenarios. It also permits comparison between different subjects. One criticism of using z-scores based on mm of change is that it does not account for magnitude of the erection [3]. This can be addressed by using a ROC curve, to provide information about the magnitude of the erection during the time of the stimulus presentation. One concern noted by Barbaree and Mewhort is that z-score transformations distort information inherent in the raw data and may also increase random error [41].
There is clinical and academic debate regarding what constitutes significant changes in penile circumference to indicate sexual arousal. Many labs use a cut-off response for significant arousal levels, while others interpret all changes in penile circumference as indicative of sexual arousal. For those that utilize a cut-off score of arousal, minimum requirements range from 1 to 6 mm of penile circumferential change [6]. Many labs use around 2.5–3.0 mm of change from baseline as research has indicated that this level represents approximately 10% of a full erection. Using 3 mm changes as the cut-off score provides improved levels of test retest reliability [6,40,42].
One concern the authors have noted in clinical practice is when subjects respond past significant levels to a neutral nonsexual stimulus. When this response pattern occurs, it brings into question the subject’s ability to differentiate between sexual and neutral nonsexual stimuli. Subsequently, when this occurs it has caused the authors to question the reliability of the subject’s other responses, including any response to sexual stimuli. One potential way to address this issue may be to calculate response after subtracting the degree of response to neutral nonsexual stimuli from the responses to all other sexual stimuli. By accounting for the baseline degree of response to neutral stimuli, the calculated arousal levels to sexual stimuli may be more accurately represented.
One way to compare a subject’s erectile response to different stimuli is to calculate indices of arousal. These indices are based on either ratio or difference scores. In published research articles, difference scores tend to be the primary approach, which consist of subtraction of the maximal response to target stimuli (i.e., pedophilic scenario) from the maximal response to comparison stimuli (e.g., nonpedophilic scenario). In contrast, some labs present the responses as a ratio index [43]. Ratio indices are calculated by dividing the highest level of response to the target stimulus (i.e., pedophilic scenario) by the highest response to comparison stimulus (i.e., nonpedophilic scenario) [3]. This ratio is referred to as the pedophile index (PI). If the PI is greater than 1.0, it indicates a stronger sexual interest in children than adults. If the PI is less than 1.0, it indicates a stronger sexual interest in adults than children. Some labs, such as the labs of the authors, also calculate a Pedophile Assault Index (PAI). The PI and the PAI are calculated similarly; however the PAI includes measurements of more physically coercive stimuli and is based on comparison pedophile stimuli only. Indices can be calculated to reflect any type of targeted sexual interest reported by the subject (such as rape, exhibitionism, voyeurism, etc.) and across any of the age and gender groups.
Conclusion
The purpose of PPG has changed from when it was first used in military recruiting stations to identify draft dodgers who were falsely claiming to be homosexual [44]. It is now used primarily in the pre-sentence phase of criminal trials and as a means to monitor change in sexual response profiles [45].The methods needed to accurately measure change in penile circumference changes are now well-established. While volumetric testing may be more effective in detecting initial changes in penile tumescence, circumferential and volumetric measures are essentially the same after 2.5 mm of change and approximately 10% of a full erection, respectively [30,42]. Since the lower levels of penile tumescence, which are detectable by volumetric testing, are also the ones with the most questionable validity, along with the fact that there is now only one lab that still uses volumetric testing [30], it is expected that circumferential testing will continue to be the standard testing apparatus.
Methods of analyzing the data from PPG testing will continue to be debated. However, it is the view of the authors that the debate should be on what analysis best suits the task at hand, rather than which analysis is “best” per se. In most cases, comparisons of indices based on ratios will lead to the same conclusions as comparisons based on differences. An open question is how to interpret test results in which a man responds significantly to pedophilic stimuli but much more to nonpedophilic stimuli resulting in a “nonsignificant pedophile index”. This scenario questions whether his response profile is less pedophilic than another man responding less to the same pedophilic stimuli, but whose overall pedophile index is higher due to a lower response to nonpedophilic stimuli. In terms of risk assessment, the first man’s higher response to pedophilic stimuli compared with the second man’s is likely more concerning. However, in terms of treatment aimed at enhancing nonpedophilic sexual interests, the second man’s response profile suggests a greater challenge given that his sexual interest in nonpedophilic stimuli is less than the first man’s nonpedophilic interest.
Another question of research interest includes the use of “provocation” tests, such as testing the subject while he is intoxicated [46–50]. This may be employed in the case of a man who committed an assault while intoxicated as an attempt to replicate his mental state and physiologic status at the time of the offense [46]. While the effects of alcohol intoxication on erectile capacity and responses is complex and not fully understood, research has been conducted in attempts to understand differences in sexual responses in sober and intoxicated subjects. When instructed, sober subjects have found to be capable of maximizing their sexual response to a significantly higher magnitude than alcohol intoxication-descending intoxicated subjects [47]. This same study also found that intoxicated subjects instructed to suppress their erectile responses produced higher magnitude of responses than intoxicated subjects instructed to maximize their erectile responses [47]. When interpreted in context with other literature investigating the effects of alcohol intoxication on men’s sexual arousal responses, George and col-leagues [47] suggest that alcohol has attenuating effects which manifest with peak arousal at a lower threshold for descending blood alcohol levels and at a higher threshold for ascending blood alcohol levels.
This research highlights the need for continued investigation on the role of alcohol intoxication and sexual arousal, as intoxicated men may be subject to different capacities when attempting to control their sexual arousal. More research and practical evaluations are required in order to increase standardized administration of PPG in conditions where the subject is tested while inebriated in attempt to replicate their physiologic state at the time of a problematic sexual encounter. Furthermore, alcohol intoxication may indirectly affect risky sexual behaviooffenser and in-the-moment motivational states, such as perceived arousal to sexual intentions, perceived intoxication, and the degree of irrational decision-making in these contexts [51].
Suppression tests in which the subject is asked to try to intentionally inhibit sexual arousal in response to sexual stimuli are another area that has not been sufficiently explored [48]. More studies concerning use of PPG in the assessment of special populations such as juveniles and men with intellectual disabilities are also needed. It is through the replication of such research that testing standardization will be achieved for these scenarios, thus improving the reliability and validity of PPG assessment.
The creation of a standardized stimulus set and a standardized protocol for assessment, analysis and interpretation of the data is of the utmost importance. Legal assessments of sex offenders, especially pertaining to courtroom testimony necessitate the development of a standardized protocol and stimuli set with reliable and proven accuracy. Nonstandardization across sites may result in competing outcomes in legal cases if the forensic psychiatry expert retained for the prosecution has the individual assessed at one lab and the expert retained for the defense has the individual assessed in another lab. In such instances, different assessment protocols and stimuli may result in conflicting findings, threatening significant forensic implications.
The authors of this article have been attempting to rectify this problem through the standardization of multisite procedures [7], interpretation and test protocol and stimuli involved in PPG assessments. The procedures, laboratories and stimuli described above provide empiric description and instruction for the creation of laboratories, use of stimuli, and interpretation of results to inform standardized, practical applications of PPG based on well-established literature and research. These practices should be regarded as an informative guideline to begin to address issues of standardization across assessment labs using PPG internationally, while continuing to promote research and standardization of the stimuli material itself used in these agencies.
Unfortunately, given legal stipulations limiting stimuli options for PPG, many locations in the United States have resorted to using other methods of assessment. Subsequently, less assessment labs in the United States rely on the use of PPG as compared with Canadian labs. There is no evidence that stimuli involving naked children are more effective than other stimuli in other modalities. The Sexual Behaviours Clinic at The Royal Ottawa Mental Health Centre (now officially known as The Royal) in Ottawa, Canada is currently collecting data regarding the efficacy of legal videotapes of children. The rationale is that legal videotapes of sexual interactions between adult actors should be arousing to subjects that do not have pedophilia. In contrast, a video of children playing at a swimming pool may be sexually exciting to men with pedophilia, but not to men without pedophilia.
Another interesting line of research involves PPG testing of subjects while under the influence of phosphodiesterase-5 (PDE-5) inhibitors, such as sildenafil and tadalafil. PDE-5 inhibitors enhance penile tumescence and delay detumescence; however, no evidence exists contending that they change sexual interest. It remains unclear whether PDE-5 assists establishing true sexual interest on PPG exams [49,50].
The future of PPG, as it currently stands, may be limited. It is a technique that measures sexual arousal at the end point of solitary sexual arousal (penile tumescence). As indicated earlier, the relationship between a man’s degree of sexual arousal and his degree of penile tumescence is far from perfect. Men are known to be highly sexually aroused but not have penile erections. Similarly, men are also known to have penile tumescence in response to rapid eye movement sleep, anxiety, depression, tactile stimulation, and other situations that make PPG testing and interpretation dependent on expert interpretation. It is expected that tests of physiologic changes in response to objective sexual arousal will eventually supplant PPG. For example, the authors of this article are currently conducting research comparing the utility of PPG and functional magnetic resonance imaging as a measure of sexual arousal in a group of men diagnosed with pedophilia as compared with healthy controls. Additionally, research comparing combined use of PPG and eye tracking is emerging as a potential assessment option [24–26]. In the meantime, PPG remains one the most well validated assessment instruments available for measurement of male sexual interests in the lab. While PPG remains the “gold standard” of assessment of sexual arousal, the implementation of multisite standardization is of critical importance.
Corresponding Author: J. Paul Fedoroff, MD, Division of Forensic Psychiatry, University of Ottawa, 1145
Carling Avenue, Ottawa, ON, Canada K1Z 7K4. Tel: 613-722-6521; Fax: 613-798-2992; E-mail: paul.fedoroff@theroyal.caConflict of Interest: Drs. Burke, Dwyer, and Federoff bill for PPG assessments in their respective labs.
Statement of Authorship
Category 1
(a) Conception and Design
Lisa Murphy, Rebekah Ranger, J. Paul Fedoroff, Hannah Stewart, R. Gregg Dwyer, and William Burke(b) Acquisition of Data
n/a
(c) Analysis and Interpretation of Data
n/aCategory 2
(a) Drafting the Manuscript
Lisa Murphy, Rebekah Ranger, J. Paul Fedoroff, Hannah Stewart, R. Gregg Dwyer, and William Burke(b) Revising It for Intellectual Content
Lisa Murphy, Rebekah Ranger, J. Paul Fedoroff, Hannah Stewart, R. Gregg Dwyer, and William BurkeCategory 3
(a) Final Approval of the Completed Manuscript
Lisa Murphy, Rebekah Ranger, J. Paul Fedoroff, Hannah Stewart, R. Gregg Dwyer, and William BurkeReferences
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