symmetry "femme battant son mari"; albrecht dürer the theory that women perpetrate intimate partner violence at roughly similar rates as men has been termed "gender symmetry". the earliest empirical evidence of gender symmetry was presented in the 1975 u.s. national family violence survey carried out by murray a. straus and richard j. gelles on a nationally representative sample of 2,146 "intact families". the survey found 11.6% of women and 12% of men had experienced some kind of intimate partner violence in the last twelve months, also 4.6% of men and 3.8% of women had experienced "severe" intimate partner violence. these unexpected results led suzanne k. steinmetz to coin the controversial term "battered husband syndrome" in 1977. ever since the publication of straus and gelles' findings, other researchers in domestic violence have discussed whether gender symmetry really exists, and how to differentiate between victim and batterer. since 1975, numerous other empirical studies have found evidence of gender symmetry in intimate partner violence. for example, in the united states, the national comorbidity study of 1990-1992 found 18.4% of men and 17.4% of women had experienced minor intimate partner violence, and 5.5% of men and 6.5% of women had experienced severe intimate partner violence. in england and wales, the 1995 "home office research study 191" found that in the twelve months prior to the survey, 4.2% of both men and woman between the ages of 16 and 59 had been assaulted by an intimate. the canadian general social survey of 2000 found that from 1994 to 1999, 4% of men and 4% of women had experienced intimate partner violence in a relationship in which they were still involved, 22% of men and 28% of women had experienced intimate partner violence in a relationship which had now ended, and 7% of men and 8% of women had experienced intimate partner violence across all relationships, past and present. the 2005 canadian general social survey, looking at the years 1999–2004 found similar data; 4% of men and 3% of women had experienced intimate partner violence in a relationship in which they were still involved, 16% of men and 21% of women had experienced intimate partner violence in a relationship which had now ended, and 6% of men and 7% of women had experienced intimate partner violence across all relationships, past and present. an especially controversial aspect of the gender symmetry debate is the notion of bidirectional or reciprocal intimate partner violence (i.e. when both parties commit violent acts against one another). findings regarding bidirectional violence are particularly controversial because, if accepted, they can serve to undermine one of the most commonly cited reasons for female perpetrated ipv; self-defense against a controlling male partner. despite this, many studies have found evidence of high levels of bidirectionality in cases where women have reported intimate partner violence. for example, social activist erin pizzey, who established the first women's shelter in the u.k. in 1971, found that 62 of the first 100 women admitted to the centre were "violence-prone," and just as violent as the men they were leaving. the 1975 national family violence survey found that 27.7% of intimate partner violence cases were perpetrated by men alone, 22.7% by women alone and 49.5% were bidirectional. in order to counteract claims that the reporting data was skewed, female-only surveys were conducted, asking females to self-report, resulting in almost identical data. the 1985 national family violence survey found 25.9% of ipv cases perpetrated by men alone, 25.5% by women alone, and 48.6% were bidirectional. a study conducted in 2007 by daniel j. whitaker, tadesse haileyesus, monica swahn, and linda s. saltzman, of 11,370 heterosexual u.s. adults aged 18 to 28 found that 24% of all relationships had some violence. of those relationships, 49.7% of them had reciprocal violence. in relationships without reciprocal violence, women committed 70% of all violence. however, men were more likely to inflict injury than women. in 1997, philip w. cook conducted a study of 55,000 members of the united states armed forces, finding bidirectionality in 60-64% of intimate partner violence cases, as reported by both men and women. the 2001 national longitudinal study of adolescent health found that 49.7% of intimate partner violence cases were reciprocal and 50.3% were non-reciprocal. when data provided by men only was analyzed, 46.9% of cases were reported as reciprocal and 53.1% as non-reciprocal. when data provided by women only was analyzed, 51.3% of cases were reported as reciprocal and 49.7% as non-reciprocal. the overall data showed 70.7% of non-reciprocal intimate partner violence cases were perpetrated by women only (74.9% when reported by men; 67.7% when reported by women) and 29.3% were perpetrated by men only (25.1% when reported by men; 32.3% when reported by women). the 2006 thirty-two nation international dating violence study "revealed an overwhelming body of evidence that bidirectional violence is the predominant pattern of perpetration; and this ... indicates that the etiology of ipv is mostly parallel for men and women". the survey found for "any physical violence", a rate of 31.2%, of which 68.6% was bidirectional, 9.9% was perpetrated by men only, and 21.4% by women only. for severe assault, a rate of 10.8% was found, of which 54.8% was bidirectional, 15.7% perpetrated by men only, and 29.4% by women only. in 2000, john archer conducted a meta-analysis of eighty-two ipv studies. he found that "women were slightly more likely than men to use one or more acts of physical aggression and to use such acts more frequently. men were more likely to inflict an injury, and overall, 62% of those injured by a partner were women." by contrast, the u.s. department of justice finds that women make up 84% of spouse abuse victims and 86% of victims of abuse by a boyfriend or girlfriend. as both fiebert and archer point out, although the numerical tally of physical acts in these studies has found similar rates of intimate partner violence amongst men and women, and high rates of bidirectionality, there is general agreement amongst researchers that male violence is a more serious phenomenon, primarily, but not exclusively, because male violence tends to inflict more psychological and physical damage than female violence. male violence produces injury at roughly six times the rate of female violence. women are also more likely to be killed by their male partners than the reverse (according to the us department of justice, 84% of spousal murder victims are female), and women in general are more likely to be killed by their spouses than all other types of assailants combined. in relation to this, murray a. straus has written "although women may assault their partners at approximately the same rate as men, because of the greater physical, financial, and emotional injury suffered by women, they are the predominant victims. consequently, the first priority in services for victims and in prevention and control must continue to be directed toward assaults by husbands." from 2010 to 2012, scholars of domestic violence from the u.s., canada and the u.k. assembled the partner abuse state of knowledge, a research database covering 1700 peer-reviewed studies, the largest of its kind. among its findings: more women (23%) than men (19.3%) have been assaulted at least once in their lifetime. rates of female-perpetrated violence are higher than male-perpetrated (28.3% vs. 21.6%). male dating students are abused more than female dating students. male and female ipv are perpetrated from similar motives. studies comparing men and women in the power/control motive have mixed results overall. a 2013 review examined studies from five continents and the correlation between a country's level of gender inequality and rates of domestic violence. the authors found that when partner abuse is defined broadly to include emotional abuse, any kind of hitting, and who hits first, partner abuse is relatively even. they also stated if one examines who is physically harmed and how seriously, expresses more fear, and experiences subsequent psychological problems, domestic violence is significantly gendered toward women as victims. conflict tactics scale in a 2002 review of the research presenting evidence of gender symmetry, michael kimmel noted that more than 90% of "systematic, persistent, and injurious" violence is perpetrated by men. he was especially critical of the fact that the majority of the empirical studies reviewed by fiebert and archer used the conflict tactics scale (cts) as the sole measure of domestic violence, and that many of the studies used samples composed entirely of single people under the age of thirty, as opposed to older married couples. although the cts is the most widely used domestic violence measurement instrument in the world, it is also one of the most criticized instruments, due to its exclusion of context variables, inability to measure systemic abuse and motivational factors in understanding acts of violence. for example, the national institute of justice cautions that the cts may not be appropriate for intimate partner violence research at all "because it does not measure control, coercion, or the motives for conflict tactics". kimmel argues that the cts is particularly vulnerable to reporting bias because it depends on asking people to accurately remember and honestly report incidents which have occurred up to a year previously. even straus admitted that the data indicates men tend to underestimate their use of violence, and women tend to overestimate their use of violence. "he attempts to control for this by examining only reports from women. yet this does not correct the bias, because women also tend to underestimate men’s use of violence. furthermore, men and women alike tend to overestimate women’s use of violence. violence by men is expected, so it is not reported; violence by women is not expected, so it is notable and reported." thus men will overestimate their victimization and underestimate their perpetration, while women will underestimate their victimization and overestimate their perpetration. barbara j. morse and malcolm j. george have presented data suggesting that male underestimation of their partner's violence is more common in cts based studies than overestimation. linda kelly has noted that even when dividing the data provided by cts based studies into that given by men and that given by women (such as in the 2001 national longitudinal study of adolescent health), the rate of female perpetrated intimate partner violence remains at roughly the same level. the dunedin longitudinal study interviewed both partners in an attempt to test for intentional bias by the participants but found a high degree of correlation between the two partners. indeed, contrary to expectations, agreement between partners did not vary with the perpetrator’s gender or with the type of abusive behavior. r. emerson dobash and russell p. dobash have also criticized the cts, arguing that it is improper to equate male intimate partner violence with female intimate partner violence. they question the methodology behind the cts, the data which stems from it and the theoretical framework used by investigators who champion it, arguing that male aggression is much more severe than female aggression and the two should not be measured by the same tool on the same scale. such an approach would make it impossible to compare male and female aggression because there would be no common measurement. another critic, kersti yllö, who holds straus and those who use the cts accountable for damaging the gains of the battered women's movement, by releasing their findings into the "marketplace of ideas". she argues that, as sociologists committed to ending domestic violence, they should have foreseen the controversy such statistics would cause and the damage it could potentially do to battered women. similarly, nancy worcester refers to studies which find evidence of gender symmetry and high levels of bidirectionality as part of the "anti-feminist backlash", arguing that studies which use the cts demonstrate the "limitations and dangers of a gender-neutral approach to anti-violence work". straus argues that it is more harmful to women to attempt to tackle the problem of domestic abuse without proper strategy based on facts: "the research shows that this so-called harmless violence by women because a meta-analysis by stith and colleagues (2004) found that a woman's perpetration of violence was the strongest predictor of her being a victim of partner violence." straus responded to criticism of the cts by arguing that it is driven by radical-feminists who are uncomfortable with any evidence that women can be as violent as men because it