Medical Studies on Circumcision
Circumcised Boys Have More Emotional and Behavioral Problems
Data collected from self-report questionnaires resulted in the following findings. Circumcised boys compared to intact boys scored higher on activity/impulsivity, aggression/defiance, peer aggression, depression/withdrawal, general anxiety, separation distress, inhibition to novelty, negative emotionality, sleep, eating, and sensory sensitivity. Circumcised boys compared to intact boys scored lower on compliance, attention, mastery, motivation, imitation/play, empathy, and prosocial peer relations.
Leone-Vespa, T. "Understanding the Relationship Between Circumcision and Emotional Development in Young Boys: Measuring Aggressiveness and Emotional Expressiveness," Alliant International University, 2011, 138 pages; 3467063.
Circumcision Decreases Penile Sensitivity
The sensitivity of the foreskin and its importance in erogenous sensitivity is widely debated and controversial. The present study shows in a large cohort of men, based on self-assessment, that the foreskin has erogenous sensitivity. It is shown that the foreskin is more sensitive than the uncircumcised glans mucosa, which means that after circumcision genital sensitivity is lost. For the glans penis, circumcised men reported decreased sexual pleasure and lower orgasm intensity. They also stated more effort was required to achieve orgasm, and a higher percentage of them experienced unusual sensations (burning, prickling, itching, or tingling and numbness of the glans penis). For the penile shaft a higher percentage of circumcised men described discomfort and pain, numbness and unusual sensations. This study confirms the importance of the foreskin for penile sensitivity, overall sexual satisfaction, and penile functioning. Before circumcision without medical indication, adult men, and parents considering circumcision of their sons, should be informed of the importance of the foreskin in male sexuality.In the present study there is strong evidence on the erogenous sensitivity of the foreskin.
Bronselaer, G. et al., "Male Circumcision Decreases Penile Sensitivity as Measured in a Large Cohort," BJU International 111 (2013): 820-827. http://www.ncbi.nlm.nih.gov/pubmed/23374102?dopt=Abstract
Father's Circumcision Status Influences Circumcision Decision
In a survey of parents attending prenatal classes, when the father of the expected baby was circumcised, 81.9% of respondents were in favor of pursuing elective circumcision. When the father of the expected child was not circumcised, 14.9% were in favor of pursuing elective circumcision. Despite new medical information and updated stances from various medical associations, newborn male circumcision rates continue to be heavily influenced by the circumcision status of the child's father.
Rediger, C. and Muller, A., "Parents' Rationale for Male Circumcision." Canadian Family Physician 59 (2013); 110-115.
Circumcision is Associated with Adult Difficulty in Identifying and Expressing Feelings
This preliminary study investigates what role early trauma might have in alexithymia (difficulty in identifying and expressing feelings) acquisition for adults by controlling for male circumcision. Three hundred self-selected men were administered the Toronto Twenty-Item Alexithymia Scale checklist and a personal history questionnaire. The circumcised men had age-adjusted alexithymia scores 19.9 percent higher than the intact men; were 1.57 times more likely to have high alexithymia scores; were 2.30 times less likely to have low alexithymia scores; had higher prevalence of two of the three alexithymia factors (difficulty identifying feelings and difficulty describing feelings); and were 4.53 times more likely to use an erectile dysfunction drug. Alexithymia in this population of adult men is statistically significant for having experienced circumcision trauma and for erectile dysfunction drug use. (See link to article on our home page.)
Bollinger, D. and Van Howe, R. , "Alexithymia and Circumcision Trauma: A Preliminary Investigation," International Journal of Men's Health (2011);184-195.
Circumcision Associated with Sexual Difficulties in Men and Women
A new national survey in Denmark, where about 5% of men are circumcised, examined associations of circumcision with a range of sexual measures in both sexes. Circumcised men were more likely to report frequent orgasm difficulties, and women with circumcised spouses more often reported incomplete sexual needs fulfillment and frequent sexual function difficulties overall, notably orgasm difficulties, and painful sexual intercourse. Thorough examination of these matters in areas where male circumcision is more common is warranted.
Frisch, M., Lindholm, M., and Grønbæk, M., "Male Circumcision and Sexual Function in Men and Women: A Survey-based, Cross-sectional Study in Denmark," International Journal of Epidemiology (2011);1–15.
Circumcision is Associated with Premature Ejaculation
Premature ejaculation (PE) is common. However, it has been underreported and undertreated. The aim of the study was to determine the prevalence of PE and to investigate possible associated factors of PE. This cross-sectional study was conducted at a primary care clinic over a 3-month period in 2008. Men aged 18-70 years attending the clinic were recruited, and they completed self-administered questionnaires. A total of 207 men were recruited with a response rate of 93.2%. Their mean age was 46.0 years. The prevalence of PE was 40.6%. No significant association was found between age and PE. Multivariate analysis showed that erectile dysfunction, circumcision, and sexual intercourse =5 times in 4 weeks were predictors of PE. These associations need further confirmation.
Tang, W. and Khoo, E. "Prevalence and Correlates of Premature Ejaculation in a Primary Care Setting: A Preliminary Cross-Sectional Study," Journal of Sexual Medicine 8 (2011); 2071-2078..
Physicians' Position on Circumcision Affected by Personal Factors
Based on responses to a survey questionnaire, physicians stated that they based their circumcision position on medical evidence. However, the circumcision status of the male respondents played a huge role in whether they were in support of circumcisions or not. Another factor that had an influence was the circumcision status of the respondents' sons.
Muller, A. "To Cut or Not to Cut? Personal Factors Influence Primary Care Physicians' Position on Elective Circumcision." American Journal of Men's Health 7 (2010); 227-232.
NOTE: There have been numerous articles in American media about claims that circumcision prevents HIV transmission. No mainstream media article has reported on an opposing view, as described in the findings of the following five medical articles.
Claim of Circumcision Benefit is Overstated and Premature
Further research is required to assess the feasibility, desirability and cost-effectiveness of circumcision to reduce the acquisition of HIV. This paper endorses the need for such research and suggests that, in its absence, it is premature to promote circumcision as a reliable strategy for combating HIV. Since articles in leading medical journals as well as the popular press continue to do so, scientific researchers should think carefully about how their conclusions may be translated both to policy makers and to a more general audience. The importance of addressing ethico-legal concerns that such trials may raise is highlighted. The understandable haste to find a solution to the HIV pandemic means that the promise offered by preliminary and specific research studies may be overstated. This may mean that ethical concerns are marginalized. Such haste may also obscure the need to be attentive to local cultural sensitivities, which vary from one African region to another, in formulating policy concerning circumcision.
Fox, M. and Thomson, M., "HIV/AIDS and Circumcision : Lost in Translation," Journal of Medical Ethics 36 (2010):798-801.
Circumcision/HIV Claims are Based on Insufficient Evidence
An article endorsed by thirty-two professionals questions the results of three highly publicized African circumcision studies. The studies claim that circumcision reduces HIV transmission, and they are being used to promote circumcisions. Substantial evidence in this article refutes the claim of the studies.
Examples in the article include the following:
- Circumcision is associated with increased transmission of HIV to women.
- Conditions for the studies were unlike conditions found in real-world settings.
- Other studies show that male circumcision is not associated with reduced HIV transmission.
- The U.S. has a high rate of HIV infection and a high rate of circumcision. Other countries have low rates of circumcision and low rates of HIV infection.
- Condoms are 95 times more cost effective in preventing HIV transmission.
- Circumcision removes healthy, functioning, unique tissue, raising ethical considerations.
Green, L. et al., "Male Circumcision and HIV Prevention: Insufficient Evidence and Neglected External Validity," American Journal of Preventive Medicine 39 (2010): 479-82.
In National Survey Circumcision Had No Protective Effect
A survey of South African men showed that circumcision had no protective effect in the prevention of HIV transmission. This is a concern, and has implications for the possible adoption of mass male circumcision strategy both as a public health policy and an HIV prevention strategy.
Connolly, C. et al., South African Medical Journal 98(2008): 789-794.
Circumcision is Not Cost Effective
The findings suggest that behavior change programs are more efficient and cost effective than circumcision. Providing free condoms is estimated to be significantly less costly, more effective in comparison to circumcising, and at least 95 times more cost effective at stopping the spread of HIV in Sub-Saharan Africa. In addition, condom usage provides protection for women as well as men. This is significant in an area where almost 61% of adults living with AIDS are women.
McAllister, R. et al., "The Cost to Circumcise Africa," American Journal of Men's Health 7(2008): 307-316.
Circumcision/HIV Have Incomplete Evaluation
The push to institute mass circumcision in Africa, following the three randomized clinical trials (RCTs) conducted in Africa, is based on an incomplete evaluation of real-world preventive effects over the long-term – effects that may be quite different outside the research setting and circumstances, with their access to resources, sanitary standards and intensive counseling. Moreover, proposals for mass circumcision lack a thorough and objective consideration of costs in relation to hoped-for benefits. No field-test has been performed to evaluate the effectiveness, complications, personnel requirements, costs and practicality of proposed approaches in real-life conditions. These are the classic distinctions between efficacy and effectiveness trials, and between internal validity and external validity.
Campaigns to promote safe-sex behaviors have been shown to accomplish a high rate of infection reduction, without the surgical risks and complications of circumcision, and at a much lower cost. For the health community to rush to recommend a program based on incomplete evidence is both premature and ill-advised. It misleads the public by promoting false hope from uncertain conclusions and might ultimately aggravate the problem by altering people’s behavioral patterns and exposing them and their partners to new or expanded risks. Given these problems, circumcision of adults, and especially of children, by coercion or by false hope, raises human rights concerns.
Green, L. et al., "Male Circumcision is Not the HIV ‘Vaccine’ We Have Been Waiting For!" Future Medicine 2 (2008): 193-199, DOI 10.2217/17469600.2.3.193.
Circumcision Decreases Sexual Pleasure
A questionnaire was used to study the sexuality of men circumcised as adults compared to uncircumcised men, and to compare their sex lives before and after circumcision. The study included 373 sexually active men, of whom 255 were circumcised and 118 were not. Of the 255 circumcised men, 138 had been sexually active before circumcision, and all were circumcised at >20 years of age. Masturbatory pleasure decreased after circumcision in 48% of the respondents, while 8% reported increased pleasure. Masturbatory difficulty increased after circumcision in 63% of the respondents but was easier in 37%. About 6% answered that their sex lives improved, while 20% reported a worse sex life after circumcision. There was a decrease in masturbatory pleasure and sexual enjoyment after circumcision, indicating that adult circumcision adversely affects sexual function in many men, possibly because of complications of the surgery and a loss of nerve endings.
Kim, D. and Pang, M., "The Effect of Male Circumcision on Sexuality," BJU International 99 (2007): 619-22.
Circumcision Removes the Most Sensitive Parts of the Penis
A sensitivity study of the adult penis in circumcised and uncircumcised men shows that the uncircumcised penis is significantly more sensitive. The most sensitive location on the circumcised penis is the circumcision scar on the ventral surface. Five locations on the uncircumcised penis that are routinely removed at circumcision are significantly more sensitive than the most sensitive location on the circumcised penis.
In addition, the glans (head) of the circumcised penis is less sensitive to fine touch than the glans of the uncircumcised penis. The tip of the foreskin is the most sensitive region of the uncircumcised penis, and it is significantly more sensitive than the most sensitive area of the circumcised penis. Circumcision removes the most sensitive parts of the penis.
This study presents the first extensive testing of fine touch pressure thresholds of the adult penis. The monofiliment testing instruments are calibrated and have been used to test female genital sensitivity.
Sorrells, M. et al., “Fine-Touch Pressure Thresholds in the Adult Penis,” BJU International 99 (2007): 864-869.
Circumcision Policy Influenced by Psychosocial Factors
The debate about the advisability of circumcision in English-speaking countries typically has focused on potential health factors. The position statements of committees from national medical organisations are expected to be evidence-based; however, the contentiousness of the ongoing debate suggests that other factors are involved. Various potential factors related to psychology, sociology, religion, and culture may also underlie policy decisions. These factors could affect the values and attitudes of medical committee members, the process of evaluating the medical literature, and the medical literature itself. Although medical professionals highly value rationality, it can be difficult to conduct a rational and objective evaluation of an emotional and controversial topic such as circumcision. A negotiated compromise between polarized committee factions could introduce additional psychosocial factors. These possibilities are speculative, not conclusive. It is recommended that an open discussion of psychosocial factors take place and that the potential biases of committee members be recognized.
Goldman, R., “Circumcision Policy: A Psychosocial Perspective,” Paediatrics & Child Health 9 (2004): 630-633.
Circumcision is Not Good Health Policy
A cost-utility analysis, based on published data from multiple observational studies, comparing boys circumcised at birth and those not circumcised was undertaken using the Quality of Well-being Scale, a Markov analysis, the standard reference case, and a societal perspective. Neonatal circumcision increased incremental costs by $828.42 per patient and resulted in an incremental 15.30 well-years lost per 1000 males. If neonatal circumcision was cost-free, pain-free, and had no immediate complications, it was still more costly than not circumcising. Using sensitivity analysis, it was impossible to arrange a scenario that made neonatal circumcision cost-effective. Neonatal circumcision is not good health policy, and support for it as a medical procedure cannot be justified financially or medically.
Van Howe, R., “A Cost-Utility Analysis of Neonatal Circumcision,” Medical Decision Making 24 (2004):584-601.
Pain, Trauma, Sexual, and Psychological Effects of Circumcision Investigated
Infant male circumcision continues despite growing questions about its medical justification. As usually performed without analgesia or anaesthetic, circumcision is observably painful. It is likely that genital cutting has physical, sexual and psychological consequences, too. Some studies link involuntary male circumcision with a range of negative emotions and even post-traumatic stress disorder (PTSD). Some circumcised men have described their current feelings in the language of violation, torture, mutilation and sexual assault. In view of the acute as well as long-term risks from circumcision and the legal liabilities that might arise, it is timely for health professionals and scientists to re-examine the evidence on this issue and participate in the debate about the advisability of this surgical procedure on unconsenting minors.
Boyle G., Goldman, R., Svoboda, J.S., and Fernandez, E., "Male Circumcision: Pain, Trauma and Psychosexual Sequelae," Journal of Health Psychology (2002): 329-343.
Circumcision Results in Significant Loss of Erogenous Tissue
A report published in the British Journal of Urology assessed the type and amount of tissue missing from the adult circumcised penis by examining adult foreskins obtained at autopsy. Investigators found that circumcision removes about one-half of the erogenous tissue on the penile shaft. The foreskin, according to the study, protects the head of the penis and is comprised of unique zones with several kinds of specialized nerves that are important to optimum sexual sensitivity.
Taylor, J. et al., "The Prepuce: Specialized Mucosa of the Penis and Its Loss to Circumcision," BJU 77 (1996): 291–295.
Circumcision Affects Sexual Behavior
A study published in the Journal of the American Medical Association found that circumcision provided no significant prophylactic benefit and that circumcised men were more likely to engage in various sexual practices. Specifically, circumcised men were significantly more likely to masturbate and to participate in heterosexual oral sex than uncircumcised men.
Laumann, E. et al., "Circumcision in the U.S.: Prevalence, Prophylactic Effects, and Sexual Practice," JAMA 277 (1997): 1052–1057.
Researchers Demonstrate Traumatic Effects of Circumcision
A team of Canadian researchers produced new evidence that circumcision has long-lasting traumatic effects. An article published in the international medical journal The Lancet reported the effect of infant circumcision on pain response during subsequent routine vaccination. The researchers tested 87 infants at 4 months or 6 months of age. The boys who had been circumcised were more sensitive to pain than the uncircumcised boys. Differences between groups were significant regarding facial action, crying time, and assessments of pain.
The authors believe that "neonatal circumcision may induce long-lasting changes in infant pain behavior because of alterations in the infant’s central neural processing of painful stimuli." They also write that "the long-term consequences of surgery done without anaesthesia are likely to include post-traumatic stress as well as pain. It is therefore possible that the greater vaccination response in the infants circumcised without anaesthesia may represent an infant analogue of a post-traumatic stress disorder triggered by a traumatic and painful event and re-experienced under similar circumstances of pain during vaccination."
Taddio, A. et al., "Effect of Neonatal Circumcision on Pain Response during Subsequent Routine Vaccination," The Lancet 349 (1997): 599–603.
Circumcision Study Halted Due to Trauma
Researchers found circumcision so traumatic that they ended the study early rather than subject any more infants to the operation without anesthesia. Those infants circumcised without anesthesia experienced not only severe pain, but also an increased risk of choking and difficulty breathing. The findings were published in the Journal of the American Medical Association. Up to 96% of infants in some areas of the United States receive no anesthesia during circumcision. No anesthetic currently in use for circumcisions is effective during the most painful parts of the procedure.
Lander, J. et al., "Comparison of Ring Block, Dorsal Penile Nerve Block, and Topical Anesthesia for Neonatal Circumcision," JAMA 278 (1997): 2157–2162.
Circumcised Penis Requires More Care in Young Boys
The circumcised penis requires more care than the natural penis during the first three years of life, according to a report in the British Journal of Urology. The clinical findings of an American pediatrician showed that circumcised boys were significantly more likely to have skin adhesions, trapped debris, irritated urinary opening, and inflammation of the glans (head of the penis) than were boys with a foreskin. Furthermore, because there are large variations of appearance in circumcised boys, circumcision for cosmetic reasons should be discouraged.
Van Howe, R., "Variability in Penile Appearance and Penile Findings: A Prospective Study," BJU 80 (1997): 776–782.
Poll of Circumcised Men Reveals Harm
A poll of circumcised men published in the British Journal of Urology describes adverse outcomes on men’s health and well-being. Findings showed wide-ranging physical, sexual, and psychological consequences. Some respondents reported prominent scarring and excessive skin loss. Sexual consequences included progressive loss of sensitivity and sexual dysfunction. Emotional distress followed the realization that they were missing a functioning part of their penis. Low-self esteem, resentment, avoidance of intimacy, and depression were also noted.
Hammond, T., "A Preliminary Poll of Men Circumcised in Infancy or Childhood," BJU 83 (1999): suppl. 1: 85–92
Psychological Effects of Circumcision Studied
An article titled "The Psychological Impact of Circumcision" reports that circumcision results in behavioral changes in infants and long-term unrecognized psychological effects on men. The piece reviews the medical literature on infants’ responses to circumcision and concludes, "there is strong evidence that circumcision is overwhelmingly painful and traumatic." The article notes that infants exhibit behavioral changes after circumcision, and some men have strong feelings of anger, shame, distrust, and grief about having been circumcised. In addition, circumcision has been shown to disrupt the mother-infant bond, and some mothers report significant distress after allowing their son to be circumcised. Psychological factors perpetuate circumcision. According to the author, "defending circumcision requires minimizing or dismissing the harm and producing overstated medical claims about protection from future harm. The ongoing denial requires the acceptance of false beliefs and misunderstanding of facts. These psychological factors affect professionals, members of religious groups, and parents involved in the practice."
Expressions from circumcised men are generally lacking because most circumcised men do not understand what circumcision is, emotional repression keeps feelings from awareness, or men may be aware of these feelings but afraid of disclosure.
Goldman, R., "The Psychological Impact of Circumcision," BJU 83 (1999): suppl. 1: 93–102
Serious Consequences of Circumcision Trauma in Adult Men Clinically Observed
Using four case examples that are typical among his clients, a practicing psychiatrist presents clinical findings regarding the serious and sometimes disabling long-term somatic, emotional, and psychological consequences of infant circumcision in adult men. These consequences resemble complex post-traumatic stress disorder and emerge during psychotherapy focused on the resolution of perinatal and developmental trauma. Adult symptoms associated with circumcision trauma include shyness, anger, fear, powerlessness, distrust, low self-esteem, relationship difficulties, and sexual shame. Long-term psychotherapy dealing with early trauma resolution appears to be effective in healing these consequences.
Rhinehart, J., "Neonatal Circumcision Reconsidered," Transactional Analysis Journal 29 (1999): 215-221
Anatomy and Function of the Foreskin Documented
A new article describes the foreskin (prepuce) as an integral, normal part of the genitals of mammals. It is specialized, protective, erogenous tissue. A description of the complex nerve structure of the penis explains why anesthetics provide incomplete pain relief during circumcision. Cutting off the foreskin removes many fine-touch receptors from the penis and results in thickening and desensitization of the glans outer layer. The complex anatomy and function of the foreskin dictate that circumcision should be avoided or deferred until the person can make an informed decision as an adult.
Cold, C. and Taylor, J., "The Prepuce," BJU 83 (1999): suppl. 1: 34–44.
Male Circumcision Affects Female Sexual Enjoyment
A survey of women who have had sexual experience with circumcised and anatomically complete partners showed that the anatomically complete penis was preferred over the circumcised penis. Without the foreskin to provide a movable sleeve of skin, intercourse with a circumcised penis resulted in female discomfort from increased friction, abrasion, and loss of natural secretions. Respondents overwhelmingly concurred that the mechanics of coitus were different for the two groups of men. Unaltered men tended to thrust more gently with shorter strokes.
O’Hara, K. and O’Hara, J., "The Effect of Male Circumcision on the Sexual Enjoyment of the Female Partner," BJU 83 (1999): suppl. 1: 79–84
Surveys Reveal Adverse Sexual and Psychological Effects of Circumcision
A survey of the 35 female and 42 gay sexual partners of circumcised and genitally intact men, and a separate survey of 53 circumcised and genitally intact men, and a separate survey of 30 genitally intact men themselves indicated that circumcised men experienced significantly reduced sexual sensation along with associated long-lasting negative emotional consequences.
Boyle, G. and Bensley, G., "Adverse Sexual and Psychological Effects of Male Infant Circumcision,". Psychological Reports 88 (2001): 1105-1106.
Foreskin Reduces the Force Required for Penetration and Increases Comfort
Masters and Johnson observed that the foreskin unrolled with intercourse. However, they overlooked a prior observation that intromission (i.e., penetration) was thereby made easier. To evaluate this observation an artificial introitus was mounted on scales. Repeated measurements showed a 10-fold reduction of force on entry with an initially unretracted foreskin as compared to entry with a retracted foreskin. For the foreskin to reduce the force required it must cover most of the glans when the penis is erect.
Taves, D., "The Intromission Function of the Foreskin," Med Hypotheses 59 (2002): 180.
Survey of Men Circumcised as Adults Shows Mixed Results
Men circumcised as adults were surveyed to assess erectile function, penile sensitivity, sexual activity and overall satisfaction. Over 80% of these men were circumcised to treat a medical problem. The response rate was 44% among potential responders. Mean age of responders was 42 years at circumcision and 46 years at survey. Adult circumcision appears to result in worsened erectile function, decreased penile sensitivity, no change in sexual activity, and improved satisfaction. Of the men 50% reported benefits and 38% reported harm. Overall, 62% of men were satisfied with having been circumcised. Note: Results may be affected by the fact that there was no sample of normal, healthy, genitally intact men for comparison.
Fink, K., Carson, C., DeVellis, R., "Adult Circumcision Outcomes Study: Effect on Erectile Function, Penile Sensitivity, Sexual Activity and Satisfaction," J Urol 167 (2002): 2113-2116.
Survey Finds Circumcision Contributes to Vaginal Dryness
The impact of male circumcision on vaginal dryness during coitus was investigated. We conducted a survey of 35 female sexual partners aged 18 to 69 years who had experienced sexual intercourse with both circumcised and genitally intact men. Women reported they were significantly more likely to have experienced vaginal dryness during intercourse with circumcised than with genitally intact men.
Bensley, G. and Boyle, G., "Effects of Male Circumcision on Female Arousal and Orgasm," N Z Med J 116 (2003): 595-596.
Early Adverse Experiences May Lead to Abnormal Brain Development and Behavior
Self-destructive behavior in current society promotes a search for psychobiological factors underlying this epidemic. The brain of the newborn infant is particularly vulnerability to early adverse experiences, leading to abnormal development and behavior. Although several investigations have correlated newborn complications with abnormal adult behavior, our understanding of the underlying mechanisms remains rudimentary. Models of early experience, such as repetitive pain, sepsis, or maternal separation in rodents and other species have noted multiple alterations in the adult brain, correlated with specific behavioral types depending on the timing and nature of the adverse experience. The mechanisms mediating such changes in the newborn brain have remained largely unexplored. Maternal separation, sensory isolation (understimulation), and exposure to extreme or repetitive pain (overstimulation) may cause altered brain development. (Circumcision is described as an intervention with long-term neurobehavioral effects.) These changes promote two distinct behavioral types characterized by increased anxiety, altered pain sensitivity, stress disorders, hyperactivity/attention deficit disorder, leading to impaired social skills and patterns of self-destructive behavior. The clinical importance of these mechanisms lies in the prevention of early adverse experiences and effective treatment of newborn pain and stress.
Anand, K. and Scalzo, F., "Can Adverse Neonatal Experiences Alter Brain Development and Subsequent Behavior? Biol Neonate 77 (2000): 69-82
Note: CRC disapproves of animal studies that involve inflicting pain.