Distinguishing Subtypes of Mutual Violence in the Context of Self-defense: Classifying Types of Partner Violent Couples using a Modified Conflict Tactics Scale

Abstract

Purpose:

The Revised Conflict Tactics Scale 2 (CTS2; Straus, Hamby, Boney-McCoy, & Sugarman, 1996) is the most widely used measure for assessing the frequency of intimate partner violence (IPV). However, it has been criticized for not capturing the context in which IPV takes place. This study examined follow-up items to each CTS2 physical assault item asking to clarify how often the act was perpetrated in self-defense.

Method:

A community sample of couples (N = 180) recruited for men’s recent violence toward women completed the project-modified Conflict Tactics Scale with Self-Defense (CTS2SD). The majority (69.5%) reported that the physical aggression in the past year was bilateral. On the follow-up items, 27% of men’s violent acts and over 22% of women’s violent acts were reportedly committed in self-defense. Men’s and women’s CTS2 physical assault perpetration scores, along with the percentage that were committed in self-defense, were entered into two-step cluster analyses.

Results:

Cluster analyses revealed three subgroups of bilateral violence: Male Self-defense, Female Self-defense, and Mutual Violence. The Mutual Violent cluster reported the most frequent physical assault, injury, men’s controlling behavior and men’s arrest for domestic violence.

Conclusions:

Findings suggest that Straus’ (2012) tripartite conceptualization of Man-only, Woman-only, and Both-violent couples is overly simplistic and fails to capture different types of bilateral aggression.

Most typologies of couples experiencing intimate partner violence (IPV) tend to find one large subset of couples reporting low levels of mutual violence (also called bilateral and situational violence) and another where there is unilateral violence where the perpetrator may have personality disorder features and power and control issues (also called intimate terrorism and characterological violence) (Babcock, Armenti & Warford, 2017; Johnson, 2008). However, few typologies examine the proximal motivations for IPV perpetration and whether these motivations differ between men and women (Langhinrichsen-Rohling, McCullars, & Misra, 2012). This study examines a modified version of the Revised Conflict Tactics Scale (CTS2; Straus, Hamby, Boney-McCoy, & Sugarman, 1996), which assesses self-defense to see if it adds to the ability to distinguish mutual violence from violence committed in self-defense in a community sample.

The CTS scales (Straus, 1979; Straus Hamby, Boney-McCoy, & Sugarman, 1996) are the most widely used measure for assessing IPV. The CTS2 has good internal consistency, construct validity, and discriminant validity (Straus et al., 1996), and validity with a variety of populations (Jones, Ji, Beck, & Beck, 2002; Lucente, Fals-Stewart, Richards, & Goscha, 2001; Newton, Connelly, & Landsverk, 2001). Epidemiological surveys using the CTS2 reveal that Americans are far more likely to be physically assaulted by a family member than by a stranger, which ledto important policy changes, including the Violence Against Women Act (Douglas, 2016). Because it measures self- and partner-perpetrated aggression, researchers can determine whether the violence in the home is unilateral or bilateral (Straus, 2012). Before he passed away in 2016, Murray Straus was focused on investigating a simple typology of heterosexual couples: Man-only, Woman-only, and Both-violent couples (Douglas, 2016). His national surveys show that typically about half of couples experiencing violence are in the Both-violent category. The other half is about equally distributed between the Man-only and Woman-only categories. For example, the sample studied for the National Comorbidity Study found 54% Both violent, 23% Man-only, and 24% Woman-only (Kessler, Molnar, Feurer, & Appelbaum, 2001).

However, since its inception, the CTS (Straus, 1979), has been criticized for failing to assess the context and purpose of violent acts (Archer, 1999; Dobash, Dobash, Wilson, & Daly, 1992; Saunders, 1986; White, Smith, Koss, & Figueredo, 2000). By comparing frequency counts, couples may be judged to have bilateral violence but one partner’s violence may be enacted only in self-defense (Saunders, 1986). While Straus concedes that some violence captured by the CTS2 reflects self-defense, he concluded that self-defense was not the predominant explanation for either women’s or men’s violence (Straus, 2012). In the International Dating Violence Survey (Gamez-Guadix, Straus, & Hershberger, 2011; Straus & Gozjolko, in press) women were asked, “If you ever slapped, grabbed, shoved, or hit your partner, or if your partner has ever slapped, grabbed, shoved, or hit you, who was the first one to do this the last time it happened?” Of the women in this study, 61% said they were the first to hit. Reviewing eight other surveys, Straus & Mickey (2012) concluded that in no studies were the majority of women acting in self-defense but in half of the studies, men were acting in self-defense more so than were women.

However, a meta-analysis on women’s motivations for their use of violence found that self-defense is typically either the first or second most common motivation for their use of IPV (Bair-Merritt et al., 2010). Of the 14 studies that ranked motivations for the use of violence (Barnett, Lee, & Thelen, 1997; Carrado, George, Loxam et al., 1996; Cascardi & Vivian, 995; Hamberger, 1997; Hamberger & Guse, 2005; Henning, Jones, & Holdford, 2005; Kernsmith, 2005; O’Leary & Slep, 2006; Olson & Lloyd, 2005; Saunders, 1986; Seamans, Rubin, & Stabb, 2007; Stuart, Moore, Hellmuth et al., 2006; Swan & Snow, 2003; Ward & Muldoon, 2007), four (Hamberger, 1997; Henning, Jones, & Holdford, 2005; Saunders, 1986; Swan & Snow, 2003) found that self-defense was women’s primary motivation (46–79%) for using IPV, with one additional study reporting self-defense as the second most common motivation (39%; Stuart et al., 2006).

Results may vary depending on how self-defense is operationalized. As Straus (2014, p 891) said, “Self-defense is a complex and often ambiguous phenomenon.” Self-defense is legally defined as violence to protect oneself from imminent bodily harm (Black, 1991), which is a mitigating factor in violence perpetration (Leisring & Grigorian, 2016). However, sometimes self-defense is operationalized to include defense from emotional abuse (Shorey et al., 2010; Wimberly, 2007), which should be considered retaliation rather than self-defense. Retaliation involves retribution for something that one’s partner has done (Flyn & Graham, 2010)—an act of revenge that carries legal consequences (Leisring & Grigorian, 2016). Retaliation is more difficult to define and has sometimes been vaguely defined as “fighting back” (Saunders, 1986). No study to date has examined self-defense directly using a structured, act-based questionnaire like the CTS2.

In Johnson’s (2008) typology of violent couples, he describes a subset of couples where the victim fights back against a partner who is both violent and controlling, that is an Intimate Terrorist. He calls this reactive type of violence Violent Resistant to avoid the legal quagmire of the term ‘self-defense.’ While the victim may be arrested for violence or even murder, he or she may be reacting with violence against an Intimate Terrorist (Johnson, 2008). Thus, we hypothesized that there would be at least two groups within Straus’ Both-violent category, one in which women were acting primarily in self-defense and another in which men were acting primarily in self-defense. Typologies are only useful insofar as they move beyond mere description and capture the differential causes, motivations, and reasons for violence (Babcock, Miller & Siard, 2003). Thus, resultant clusters were compared on other variables including injury, controlling behavior, severity of violence, and domestic violence arrests.

Method

Participants

A racially diverse community sample of partner violent couples (N = 180 couples; 360 individuals) was recruited via local newspaper advertisements in a large southwestern United States city. Participants were recruited as part of two larger projects investigating emotional reactivity and IPV among violent men (Babcock, Graham, Canady & Ross, 2011; Babcock, Roseman, Green, & Ross, 2008). The advertisements called for “couples experiencing conflict.” The couples were required to be married or living together as if married for at least six months prior to participation, at least 18 years of age, in a heterosexual relationship, and able to read and write English fluently. Interested couples were contacted by phone by trained undergraduate research assistants in order to be admitted into the study. To meet preliminary telephone screening, female partners had to report 1) at least two incidents of male-to-female physical aggression in the past year or 2) report no male-to-female violence ever and score less than 4 out of 7 on the Dyadic Adjustment Scale (Spanier, 1976) item #31: “On a scale from 1 to 7 where 1 is “very unhappy,” 4 is “happy,” and 7 is “perfectly happy,” where would you rate your present relationship?” Men’s relationship satisfaction and women’s violence was free to vary. The majority (80.5%) of these couples recruited reported some physical aggression in the past year; only those couples were analyzed here. Average age for male participants was 32.0 years (SD = 10.2) and average age for female participants was 29.9 years (SD = 9.4). Participants reported an average annual family income of $20,344 (SD = 34,079). The racial breakdown of the sample was as follows: 54.2% African American, 26.7% Caucasian, 14.5% Hispanic, 0.8% Asian, 0.8% Native American, and 3.1% ‘Other’ racial identity.

Procedure

Data was collected over two separate three-hour assessment periods as part of a larger experiment. During the first session, male participants came into the laboratory to fill out paper and pencil questionnaires. During the second session, both male and female participants filled out paper and pencil questionnaires separately and were later reunited for a series of structured relationship interviews and conflict discussion tasks. At the conclusion of participation, male and female participants were debriefed and received payment separately. Couples were paid $90 to $100 for their participation in both assessments ($10 extra if they appeared on time for their first scheduled appointment).

Safety Measures and Exclusion Criteria

This project was fully reviewed and approved by the University Social Sciences IRB panel. Female participants were informed of the nature of the experiment via telephone, before coming in to the lab, and were asked not to participate if they anticipated increased violence from their partner. Couples were excluded if they felt unsafe speaking their mind in front of their partner in the lab. The participants were debriefed separately to assess danger potential and develop a safety plan, if needed. Both male and female participants were given an adjective checklist to assess their emotional states. Participants endorsing any negative emotions other than “feeling somewhat negative” were interviewed on their likelihood of becoming violent in the near future. All participants were given referrals for community resources including, but not limited to, counseling services, domestic violence shelters, and drug and alcohol treatment. Finally, follow up phone interviews were conducted one week after participation with female participants to ensure that participation did not result in a violent incident. No participant reported violence due to participation in the study.

Measures

Intimate Partner Violence and Self Defense.

The Conflict Tactics-2SD.

The CTS2 (Straus et al., 1996) is a 78-item questionnaire that measures instances of both male-to-female and female-to-male physical, psychological, and sexual coercion and injury in the preceding year. The physical assault subscale is made of 12 items, including seven severely violent items (used a knife or gun, punched or hit, choked, slammed into a wall, but up, burned or scaled, kicked) In the current study, we modified the CTS2 by adding self-defense context items after each physically aggressive item. Specifically, after participants circled the frequency of each physical aggression item on the standard eight- point scale of the CTS2 (once, twice, 2–5 times, 6–10 times, 11–20 times, more than 20 times, not in the past year but before, and it has never happened), they denoted how frequently that act occurred in self-defense. Each partner reported on their own self-defense asking, “How many of those times was it in defending yourself against your partner’s violence?” on a six-point scale (once, twice, 2–5 times, 6–10 times, 11–20 times, more than 20 times, and it has never happened). The option for “not in the past year but before” was omitted from the self-defense items, as it is not a frequency. Participants also quantified their partners’ frequency of acts of self-defense after each physical aggression items, denoting. “How many of those times was it to defend against your violence?” on the six-point scale. In the current study, Cronbach’s α for the physical assault subscale was .74 for women and .96 for men The internal consistency was somewhat lower for the severe violence subscale, α = .54 for women’s and .68 for men’s perpetration. Cronbach’s α for the project-designed self-defense scale was .61 for women and .94 for men.

Balanced Inventory of Socially Desirable Responding (BIDR).

The BIDR (Paulhus, 1998) is a 40-item measure assessing two factors of social desirability: self-deceptive enhancement (SDE) and impression management (IM). Scores on each scale range from 0–20. The BIDR was administered to men only alongside the CTS-2SD to determine whether subjects were reporting self-defense accurately or claiming self-defense as a way to minimize their violence. In the current dataset, Cronbach’s α was .70 for SDE and .83 for IM.

Controlling behavior.

The Emotional Abuse inventory (EA; Murphy & Hoover, 1999 was administered to female partners only. Women reported on their own and their partners’ behavior in the past year. This 28-item measure yields four subscales using a frequency count scale similar to that of the CTS2. Participants were asked to report how often they and their partner engaged in each behavior in the past 6 months on a 7-point frequency scale (never, once, twice, 3–5 times, 6–10 times, 11–20 times, and more than 20 times). Restrictive Engulfment involves tracking, monitoring, limiting the partner’s activities and social activities. Hostile Withdrawal involves avoidance or stonewalling of the partner during conflict. Denigration involves humiliating or degrading partner with verbal put-downs. Finally, Dominance/Intimidation involves threats, property violence, and intense verbal aggression. Controlling behavior was operationalized as the sum of Restrictive Engulfment and Dominance/Intimidation. Alphas in the current dataset of this Controlling Behavior scale were .86 for women’s behavior and .91 for men’s behavior.

Criminal history.

Men and women self-reported if they had ever been arrested for domestic violence, and if so, how many times. These reports were not corroborated with a criminal records check.

Data analytic plan.

Two-step cluster analysis in SPSS version 24.0 was chosen to empirically cluster couples into group. Two-step combines the benefits of K-means with hierarchical cluster analysis by first finding the optimal number of clusters empirically and then fitting cases into the groups based on likelihood distance (Norušis, 2009). While two-step cluster analysis allows for continuous and categorical data, it performs best when the data are continuous (Bacher, 2004), as they are here. Each partners’ frequency of victimization in the past year along with their self-reported percentage of perpetration of violence committed in self-defense was z-transformed and entered into the cluster analyses as the predictor variables. Relative importance and mean of each predictor variable was compared across cluster. Next, clusters were compared on variables of interest using a MANOVA.

Results

Of the 180 couples reporting some IPV in the past year, men’s violence averaged at approximately 15 acts per years, ranging from 0 – 177 acts, as reported by their female partners. Women’s perpetration of violence averaged around 19 acts, ranging from 0 – 146 acts in the past year, as reported by their male partners (see Table 1). Three (1.9%) of the women and 22 (13.9%) of the men reported that they had been arrested for domestic violence. To examine what proportion of violent acts perpetrated were enacted in self-defense, we calculated a percentage by dividing the number of acts enacted in self-defense by the total number of violent acts. Examining the severity of the violence, women reported that 24% of her self-defense was severely violent (e.g., kicked, beat up, choked, used a weapon) whereas men reported that 28% of his self-defense was comprised of such severely violent acts. While the mean percentages of violent acts reported in self-defense appear to be reasonable, averaging between 69% and 81% of the time for men and 38% to 39% for women, the problem arises in the range of percentages. It was not uncommon, for men especially, to report more acts of violence committed in self-defense than did acts of violence. About a fifth of violent men (22.8%) reported that their violence was in self-defense more than 100% of the time. For women, 10% reported that their own violence was committed in self-defense more than 100% of the time. This may be due to them including acts prior to the past year, misunderstanding the question, or to justify their own physically aggressive acts. To explore this, we correlated percentage of violence in self-defense to arrest history and desirable responding. Men’s report of his own and his partner’s self-defense percentage was negatively related to self-deceptive enhancement (r = −.14, p = .034) and impression management (r = −.18, p = .009) but positively related to the number of arrests for domestic violence that he reported (r = .33, p < .001).

Table 1.

Overall CTS2 Subscale Mean Frequencies, Ranges and Self-defense Percentages as Reported on the Modified CTS2 (N = 180)

	Frequency of violent acts in past year Mean (SD)	Raw Percentage in Self-defense	Corrected Percentage of IPV in Self-defense	Frequency Range (# acts in past year)
Male physical assault perpetration
Male Report	15.02 (26.17)	69.37%	22.21%	0–177
Female Report	15.44 (21.09)	81.32%	33.58%	0–100
Female physical assault perpetration
Male Report	18.71 (28.06)	39.31%	26.70%	0–146
Female Report	14.30 (20.75)	38.53%	22.21%	0–127
Male psychological abuse perpetration
Male Report	34.91 (31.00)			0–175
Female Report	42.51 (33.77)			0–166
Female psychological abuse perpetration
Male Report	44.32 (31.00)			0–156
Female Report	41.56 (32.66)			0–144
Male injury
Male Report	2.36 (6.62)			0–51
Female Report	2.08 (4.78)			0–34
Female injury
Male Report	2.3 (5.31)			0–34
Female Report	3.52 (7.22)			0–50

To make sense of these data in all future analyses, scores greater than 100% were recalculated to a simple 100%. Corrected this way, men reported that their violence was committed in self-defense 27% of the time and women reported that their own violence was committed in self-defense 22% of the time, which is more in line with previous research (Bair-Merritt et al., 2010).) Correlations between men’s and women’s assault frequency and self-defense percentage were examined (See Table 2). Whereas men’s and women’s assault frequency was highly correlated, men’s and women’s self-defense were uncorrelated. Self-defense percentage was also correlated with frequency partners’ report of assault. Two-step clustering method was used in SPSS version 24, empirically choosing the number of clusters. Cluster analyses were conducted first on the whole sample. The CTS2 physical abuse and self-defense subscales as reported by both men and women were z-transformed and entered into cluster analysis. The two-group cluster solution was a poor fit, yielding 93.8% falling into Cluster 1 with no significant differences between the clusters due to lack of power.

Table 2.

Correlations among the CTS2SD Variables Entered into Cluster Analysis

	Female Self-defense percentage	Male Self-defense percentage	Male Physical Assault Frequency	Female Physical Assault Frequency
Female Self-defense percentage	--	.079	.338***	.141*
Male Self-defense percentage		--	.173*	.222**
Male Physical Assault Frequency	.		--	.345***

Notes:

^*p < .05.

^**p < .01.

^***p < .001.

Next, two-step cluster analyses were conducted to explore subgroups within Straus’ Both-violent subtype specifically. Based on partner reports of physical assault in the past year, 33 (15.5%) were Female-only Violent, 32 (15%) were Male-only Violent, and 84 (40.8%) were Both-violent, that is both partners scored greater than zero on the physical assault scale. Only couples meeting this criteria for Both-violent were entered into two-step cluster analysis (n = 84). The physical abuse frequency and self-defense variables were entered for this group only using two-step Cluster method in SPSS. Cluster solutions yielded a three-group solution within this group The silhouette of cohesion was good (.61) and the means of the predictor/input variables were distinct, with men’s self-defense score carrying the most importance in the separation of the clusters (see Table 3). A MANOVA age, education and income revealed were no significant demographic differences by cluster. Cluster 1 (25.3%) appears to reflect a truly mutually violent cluster of couples, with high rates of both violence and self-defense reported by both partners. Cluster 2 (34.5%) reflects couples where the man appears to be victimized more often than the woman, reporting high rates of her violence and his own self-defense. Women’s reports confirm this pattern. Cluster 3 (40.2%) represented mutually violent couples where the man appeared to be the primary aggressor and a large percentage of women’s violence was enacted in self-defense (See Figure 1). A MANOVA of the differences between the resultant three clusters reveals that the Mutually Violent cluster reports the most frequent violence, injury, and significantly more male arrests for domestic violence as compared to the self-defense clusters (see Table 3). Simple contrasts compare the means Female Self-defense and Male Self-defense clusters to the Mutually Violent Cluster. Both partners in Cluster 1 report high rates of both violence and self-defense. This appears to be the most dangerous group, with high rates of injury and arrest. Men only in Cluster 2 reported that the majority of their violence in self-defense, with 88% of the CTS2 acts purportedly conducted in self-defense. Women only in Cluster 3 reported that their violence was motivated by self-defense 41% of the time. Approximately 25% of the men and 3% of the women reported having been arrested for domestic violence in the past. Both partners were more likely to be injured in the Mutually Violent cluster compared to couples in the other two clusters. Men, but not women, in the Mutually Violent cluster were more controlling than men in the other two clusters. Men, but not women, in the Mutually Violent cluster were more likely to have been arrested. Finally, there were differences by cluster on the use of severe violence enacted in self-defense. Specifically, men’s self-defense in the Male Self-defense group (Cluster 2) included a greater proportion of severely violent acts as compared to men in the other two clusters.

Table 3:

Predictor and Importance and Centroid Means and SDs by Cluster

		Cluster 1 Mutual Violence	Cluster 2 Male Self-Defense	Cluster 3 Female Self-Defense
	Predictor Importance	Mean (SD)	Mean (SD)	Mean (SD)
Female Self-Defense	.24	.69 (1.12)	−.64 (.46)	.11(.95)
Male Self-Defense	1.0	.21 (.90)	.98 (.41)	−.97 (.22)
Men’s Physical Assault	.35	1.11 (1.23)	−.45 (.53)	−.31 (.53)
Women’s Physical Assault	.43	1.01 (1.45)	−.19 (.49)	−.47 (.32)

Note: All input/predictor variables were standardized. Self-defense was self-reported by men and women. Physical assault frequency was based on partner report on CTS2 physical assault scale.

Figure 1:

Percentage of Sample with Male-only, Female-only and Mutual Violence and Subtypes Note: 69.5% of the sample reported mutual/bilateral violence. The percentages reported within the Mutual Violence pie chart are within that 69.5%.

Discussion

Perhaps the most controversial finding of survey research regarding IPV is the finding that women are as equally violent as men. While feminist scholars have argued that these frequency counts are inflated by women’s self-defense (Baker, 1991), few researchers have tried to parse out the frequency of self-defense from the overall frequency of violent acts. Examining self-defense as it maps on to each item on the CTS2 may be one way to help capture and clarify the context of IPV. Survey research that relies exclusively on frequency counts of men’s and women’s physically aggressive acts and labeling a large group as mutual or bilateral violence misses the context of both partners’ abuse as potentially in defense against their partner’s violence.

Subtypes within the mutually violent group of couples emerged, not distinguishable on CTS2 scores alone. A large subset of bilaterally violent couples emerged where the woman was violent in self-defense 41% of the time. Even in a community sample recruited for men’s violence towards women, there emerged a sizable cluster of couples in which the woman was the primary aggressor or the man was violent 88% of the time in order to defend himself. The majority of the time, these men in the Male Self-defense cluster resorted to using severely violent acts in order to defend himself. Other studies have found that women are more prone to use severe violence, including weapons, due to differences in upper body strength (Dutton, 2006). Given the differences in upper body strength between the sexes, it is dubious why a man would need to resort to severe violence against a woman in self-defense. Although men’s impression management was negatively correlated to his self-defense frequency, men may be using claims of self-defense to minimize or justify their use of severe IPV.

A simple addition to the CTS2 reveals that a large proportion of physically aggressive acts—especially those perpetrated by men--were enacted in self-defense. While Straus (2011, p. 283) acknowledged that, “Some bi-directional violence is the result of attacks by men, to which women respond in self-defense,” he suggested that the percentage is low, being less than 15%. However, when participants were asked about self-defense item by item, the percentage of acts committed in self-defense appears to be quite high. Our findings that over 27% of men’s violent acts and over 22% of women’s violent acts were committed in self-defense. In general, women were more likely than men to report that her partner’s violence was enacted in self-defense. This finding that the rates of self-defense are higher for men than for women is consistent with another study on undergraduate and graduate students (Harned, 2001). However, in one emergent subgroup of mutually violent couples, the majority of men’s violence was purportedly enacted in self-defense. Most studies of violence motivations assess self-defense using a single item (Babcock et al., 2003; Harned, 2001). When asked on an item by items basis, reports of self-defense appear to be much higher than with a single item question of motivation for the use of violence. To assume these three clusters are all mutual combatants or simply “both violent” (Straus, 2014) implies equal culpability and intent.

The Mutually Violent cluster of couples appears to be the most at risk for injury and arrest. While both partners in this cluster report violence in self-defense approximately half of the time, this type of couple is distinct for the sheer frequency of violence committed by both partners and by men’s controlling behavior. Some of both partners’ violence appears to be offensive in nature. This cluster appears to best map on to Johnson’s (2008) Intimate Terrorist subgroup. While fighting back is thought to be a risk factor for escalating partner violence and increased risk for injury for women (Archer, 2000; Saunders, 1986), self-defense in the absence of offensive violence and controlling behavior could serve as a protective, de-escalation strategy. Bilateral offensive violence and men’s controlling behavior appears to be the biggest risk factor for escalating abuse.

Limitations

The current community sample was recruited for recent male-to-female intimate partner conflict, as the primary aim of the study was to examine patterns of emotional reactivity among violent men. Nonetheless, we recruited a significant number of couples (15%) in which only the woman was violent. Findings may not generalize to shelter samples or broad national surveys. Representative surveys find a larger proportion of female-only violent couples and the cluster solutions may not be replicable. This was a cross-sectional study and these resultant clusters may not be stable over time. Couples may change in the degree to which they use offensive and defensive violence over the course of their relationship. While most of the measures were given in parallel, some measures were administered only to the women (EA) or to the men (BIDR). In addition, the number of cases entered into cluster analysis after sorting out couples with male-only and female-only violence was relatively small.

In studies of motivations for violence, self-defense and retaliation are common motivations, but there are difficulties in delineating the two concepts (Bair-Merritt et al., 2010). Although this modification to the CTS2 appears to be clearly stated, “How many of those times was it in defending yourself against your partner’s violence?” no explicit definition of “defending yourself” was provided. Participants may have been acting in a retaliation for their partner’s past violence rather than in immediate self-defense. That is, they could have been acting with delayed violence that is reacting to their partners’ past violence. Another wording option might be, “How many of those times were you acting to protect yourself from immediate physical harm?” so that it maps on to the legal definition of self-defense (Leisring, 2013; P. Leisring, personal communication, November 27, 2017). It remains unclear why some participants reported that their violence was in self-defense more than 100% of the time, that over-reporting did not appear to be caused by impression management. The wording of the self-defense follow-up question may have been unclear or confusing.

While our modification added some context to the CTS2 items, there are other contextual factors that are not captured with the addition of self-defense items. Whether the partners are controlling or in living in fear are features of the characterological versus situational violence dichotomy are other variables that may provide useful data in sorting types of couples. While asking about self-defense motivations to each act of physical aggression on the CTS2SD may trigger more accurate recall, it may be unnecessarily exhaustive. It may be sufficient to simply ask one question about what percentage of the physically aggressive acts were committed in self-defense. Future studies could compare both methods of assessing self-defense, as it has profound implications to the interpretation of surveys of intimate partner violence. Future studies may also examine the change in mutuality of violence and self-defense behavior over time in longitudinal studies.

Clinical implications

Currently, no distinction is made as to what the motive was for intimate partner violence in considering battering interventions. Men acting in self-defense would be arrested and sent to the same battering intervention program as would an intimate terrorist. Women, too, could be arrested for violence committed in self-defense and few communities offer interventions tailored to the needs of women arrested for IPV. The mutually violent subgroup reported the most violence, injuries, controlling behavior and arrests for domestic violence. While some of their violence is reportedly committed in self-defense, both partners appear to be engaging in offensive violence. They may lack the de-escalation strategies to prevent harmful fights. This subgroup is the most dangerous and most in need of intervention, perhaps with mandated interventions for both partners. In the future, interventions may be tailored to different types of couples where one or both partners has been arrested, taking into account self-defense and control motives for IPV perpetration.

Straus’ (2012; October 2013) “simple and powerful” tripartite conceptualization of Man-only, Woman-only, and Both-violent couples is perhaps too simple. It fails to capture different subtypes within the Both-violent group. To assume that all couples who are both violent are mutual combatants implies equal culpability and intent. What would be labeled Both-violent based on frequency counts alone fails to capture the subtype within this group that Johnson (2008) calls Violent Resistance, in which one partner is predominantly fighting back to protect him or herself. Examining whether the proximal motivations for violence perpetration differs between different types of couples may highlight potential treatment targets by which to reduce IPV (Langhinrichsen-Rohling et al., 2012). To consider Both-violent couples as a monolithic group ignores a sizable subset that are frequently violent in self-defense. While the field needs a user-friendly tool to triage couples into alternative therapies, adding self-defense contextual items to the CTS2 is one step in that direction.

Table 4.

Three Clusters Within the Mutually Violent group: Differences on Violence, Control and Arrest History by Cluster

	Cluster 1Mutual Violence (n = 21; 25%)	Cluster 2 Male Self-Defense (n = 29; 34.5%)	Cluster 3 Female Self-Defense (n = 34; 40.2%)	F (2,81)
Men’s Physical Assault
Women’s report	50.37a (30.46)	13.68b (13.13)	16.23b (12.71)	27.82***
Men’s self-report	50.19a (47.39)	16.07b (16.49)	12.82b (17.46)	13.22***
Women’s Physical Assault
Women’s self-report	32.38a (22.60)	22.75b (28.70)	13.33b (14.04)	4.88*
Men’s report	63.33a (47.00)	21.49b (16.24)	12.27b (10.70)	26.61***
Self-defense percentage
Women’s self-report	0.66a (.41)	0.13b (.18)	0.41a (.36)	16.34***
Men’s self-report	0.53a (.38)	0.88a (.18)	0.05b (.43)	108.08***
Injury
Women’s self-report	15.40a (13.78)	1.89b (3.51)	2.97b (3.60)	21.58***
Men’s self-report	8.05a (12.48)	3.64b (4.05)	0.63b (1.73)	7.02**
Controlling behaviort
Men’s	209.33a (159.92)	71.63b (93.77)	132.65b (144.35)	6.57**
Women’s	108.133 (129.75)	104.90 (99.33)	104.71 (115.29)	2.84
DV arrests
Women’s self-report	.67a (1.43)	.30a (.61)	.07a (.25)	0.03
Men’s self-report	.05a (0.22)	.047a (.19)	.03ba (.18)	3.20*
Severely violent self-defense1
Women’s self-report	.23a (.21)	.33a (.35)	.17a (.18)	1.59
Men’s self-report	.28a (.30)	.57b (.78)	.07a (.18)	3.53*

Notes:

^twomen’s report only;

^*p < .05;

^**p < .01;

^***p < .001

¹Proportion of self-defense comprised of severely violent acts Means of clusters with different superscripts are significantly different, p < .05.