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Article

Substance Use, Aggression Perpetration, and Victimization: Temporal Co-occurrence in College Males and Females

Gayla Margolin, PhD,1 Michelle C. Ramos, PhD,1 Brian R. Baucom, PhD,1,2 Diana C. Bennett, MS,2 and Elyse L. Guran, BA1

Abstract Many studies have documented associations of substance use with aggression perpetration and aggression victimization; however, little is known about the co-occurrence of these problem behaviors within the same day in college students. The present study investigated whether substance use and aggression increase the likelihood of each other and whether attitudes justifying aggression strengthen those associations. College student participants (N = 378, 32% males) self-selected into an online study in which they reported on 2 days of alcohol/drug use and on aggression perpetration and victimization (including physical, psychological and electronic aggression, and sexual coercion) with friends and dating partners. Using regression to test for nonequivalence of predictor and outcome variables, we found bidirectional effects for males only. Males’ substance use was associated with an increased likelihood on the same day of aggression perpetration and of aggression victimization; males’ aggression perpetration and aggression

1Department of Psychology, University of Southern California, Los Angeles, CA, USA 2Department of Psychology, University of Utah, Salt Lake City, UT, USA

Corresponding Author: Gayla Margolin, University of Southern California, Psychology Department-SGM 930, 3620 S. McClintock, Los Angeles, CA 90089-1061, USA. Email: [email protected]

488683 JIV281410.1177/0886260513488683Journal of Interpersonal ViolenceMargolin et al. research-article2013

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victimization were associated with an increased likelihood of substance use on the same day. Females did not show significant contingencies between substance use and aggression in either direction. Males’ attitudes justifying male-to-female aggression were associated with their aggression perpetration and victimization and their justification of female-to-male aggression strengthened the link between substance use and aggression perpetration. With interpersonal aggression and substance use being significant problems on college campuses, many colleges offer separate preventive intervention programs aimed at these public health challenges; this study suggests possible benefits of an integrated approach that addresses connections between alcohol/drug use and aggression.

Keywords substance use, aggression, victimization, college students

Substance use and interpersonal aggression are important public health chal- lenges on college campuses. Over 40% of college students engage in risky drinking and 20% use illicit drugs in a 30-day period (Ham & Hope, 2003; Hingson, Zha, & Weitzman, 2009; Johnson, O’Malley, Bachman, & Schulenberg, 2009). In addition, approximately 30 to 40% of college students report initiating or being the target of physical aggression with someone dur- ing the previous year (Leonard, Quigley, & Collins, 2002); similar figures have also been reported for perpetrating or sustaining physical aggression specifically in dating relationships (Straus, 2008; Taft, Schumm, Orazem, Meis, & Pinto, 2010; White & Koss, 1991). Substance use and involvement in aggression—whether as the perpetrator or victim—pose risks for physical injury and adverse health and social consequences. Toward the goal of reduc- ing these risky behaviors, it is important to understand the links between aggression and substance use and, in particular, to investigate temporally proximal and reciprocal influences: To what extent are these risky behaviors linked in time such that each one potentially instigates or exacerbates the other? As contrasted with the more commonly researched question of whether substance use increases the likelihood of aggression, the present study inves- tigates bidirectional influences including whether aggression changes the likelihood of substance use. Moreover, even if evidence for proximal risks between substance use and aggression is found, it is important to identify which individuals are prone to these risks. Building on recent theories that distal, individual difference variables interact with the temporally proximal

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variables to increase risk (Bell & Naugle, 2008; Moore, Elkins, McNulty, Kivisto, & Handsel, 2011; Stuart et al., 2006), the present study investigates whether attitudes justifying aggression strengthen proximal links between substance use and aggression perpetration or victimization.

The preponderance of evidence linking substance use and aggression is based on frequencies over extended time frames, for example, a year. Such associations, however, may simply reflect general propensities for engaging in problem behaviors. In adolescents and young adults, past year dating vio- lence was associated with risky drinking (Rothman et al., 2011); likewise, problem drinking and marijuana use was associated with dating violence per- petration (Reyes, Foshee, Bauer, & Ennett, 2011) and victimization for both males and females (Buzy et al., 2004; Reingle, Staras, Jennings, Branchini, & Maldonado-Molina (2012); Silverman, Raj, Mucci, & Hathaway, 2001). A review of problem drinking and intimate partner aggression in adults (Foran & O’Leary, 2008) showed considerable variability with stronger associations for individuals in treatment for either domestic violence or substance abuse than in general population samples. A review of drug abuse and intimate part- ner aggression showed significant associations for both males and females, particularly for cocaine and marijuana use (Moore et al., 2008). A third review specific to college samples (Shorey, Stuart, & Cornelius, 2011) reported strong associations between problems with alcohol and violence perpetration for males and females as well as some evidence for alcohol use and victimization. The general associations in much of this literature do not reveal the explanatory mechanisms in the links between substance use and violence.

Although there are a number of similarities between males’ and females’ patterns of substance use and aggression, there are also some gender-specific findings. Males’ substance use is linked most consistently to aggression per- petration (e.g., Cunradi, Ames, & Duke, 2011). However, several earlier stud- ies, particularly those involving domestic violence, only included males and only assessed violence perpetration, as have some studies of college samples (Lundeberg, Stith, Penn, & Ward, 2004). A recent study, in contrast, showed drug and alcohol use for men who are recipients of intimate partner violence (Hines & Douglas, 2012). Likewise, gender-specific findings for women show strong links between substance use and victimization (Nolen-Hoeksema, 2004). Nonetheless, a growing number of recent studies has revealed links between women’s substance use and their own aggression perpetration (Caetano, Ramisetty-Mikler, & Harris, 2008; Luthra & Gidycz, 2006; Moore et al., 2008; Stuart, Moore, Ramsey, & Kahler, 2003). As the intimate vio- lence literature overall moves toward more nuanced investigation of male– female similarities and differences (Straus, 2009), direct comparisons

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between males and females that include both aggression perpetration and victimization are needed to draw gender-based conclusions about substance use-aggression links.

Proximal Connections Between Substance Use and Aggression

Theoretical explanations on proximal links between substance use and aggression suggest influences in both directions though most research has investigated how substance use increases the likelihood of aggression. On the one hand, the pharmacological effects of alcohol and other substances may have a disinhibiting effect on aggression perpetration through their impact on executive functioning (Giancola, 2000; Moore et al., 2008). Alternatively, substances may be used as a coping strategy to manage the tension and dis- tress resulting from interpersonal aggression (Fossos, Kaysen, Neighbors, Lindgren, & Hove, 2011; Taft et al., 2010). In adult samples, male-to-female aggression and more severe aggression tended to occur during or shortly after substance use (Murphy, Winters, O’Farrell, Fals-Stewart, & Murphy, 2005; Testa, Quigley, & Leonard, 2003). When college students retrospectively reported on their most recent abusive incident, drinking within 3 hr of an argument predicted women’s use of verbal and physical aggression and men’s use of verbal aggression (Shook, Gerrity, Jurich, & Segrist, 2000). Moore and colleagues (2011) recently collected 2 months of daily electronic diary reports from 146 female and 38 male college students. Their data revealed increased odds, particularly for males, of physical and psychological aggression perpe- tration on days of drinking but did not examine whether aggression perpetra- tion increased the odds of drinking. Daily data from a sample of college women showed that sexual, verbal, and physical aggression were signifi- cantly higher on days of heavy drinking, and alcohol use was higher in the 24 hr following verbal aggression only (Parks, Hsieh, Bradizza & Romosz, 2008); this study is notable for examining bidirectional aggression as well as aggression with friends in addition to dating partners—but it did not differen- tiate perpetration and victimization and did not include males. In sum, despite the growing attention to proximal effects, the existing studies generally focus on unidirectional effects, namely the influence of substance use on aggres- sion, and do not address both aggression perpetration and victimization.

Attitudes About Aggression

There is growing evidence that individual difference variables relate to sub- stance use and aggressive behavior as well as to links between these risky behaviors (Caetano et al., 2008; Sullivan, Cavanaugh, Ufner, Swan, & Snow,

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2009). As contrasted with unalterable characteristics such as gender, ethnic background, and age that affect substance use and aggression, modifiable variables deserve attention as possible targets for intervention. In general, attitudes tend to play an important role in decisions about engaging in unhealthy or harmful behaviors (Figner & Weber, 2011). Relatedly, attitudes justifying relationship aggression are associated with higher male and female aggression perpetration (Cauffman, Feldman, Jensen, & Arnett, 2000; Foo & Margolin, 1995; Schumacher & Slep, 2004). Beyond pair-wise associations between attitudes and aggressive behaviors, a question yet to be examined is whether attitudes justifying aggression strengthen the link between substance use and aggression perpetration or victimization.

Current Study

The present study is designed to investigate the co-occurrence of substance use, aggression perpetration, and aggression victimization in a sample of col- lege students—a target population for these problems. Our data represent 2 consecutive days in the lives of these participants so that we can compare within-day and across-day links. Expanding on previous studies that only examine unidirectional effects, the present study examines bidirectional effects. As contrasted with most previous studies where participants identi- fied specific aggressive episodes and then reported on associated substance use, our method examines arbitrary days to investigate the co-occurrence of substance use and aggression as well as the likelihood of substance use with- out aggression and, alternatively, aggression without substance use. Comparing conditional probabilities to base-rates of each behavior thus avoids the possibility of upward bias. In addition, because this study involved over 200 questions, participants were not alerted to our interest in the link between substance use and aggression. Another distinctive feature of this study is the assessment of aggression with friends as well as dating partners. This decision reflects assumptions about the salience of aggression—particu- larly psychological aggression—with friends, the sometimes ambiguous des- ignation of someone as a friend versus dating partner, the possibility of multiple dating partners, the fact that many college students do not live with their dating partners and may not see them on a daily basis, and our wish to include all college students, not just those with dating partners.

We hypothesized that there would be an increased likelihood for aggres- sion perpetration and victimization on days with substance use and, alter- natively, an increased likelihood for substance use on days with aggression perpetration and victimization. We also investigated across-day associa- tions to test whether these behaviors persist or reset from one day to the

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next. We hypothesized minimal across-day links, particularly after accounting for variance due to perpetration-victimization associations, a well-documented finding in college samples (Straus, 2008). We investi- gated whether gender moderated our regression analyses and, in the within-day and across-day analyses, we ran separate models for males and females and then tested whether individual paths differed across the sexes. Finally, we tested the hypothesis that attitudes justifying aggression would strengthen the link between substance use and aggression perpetration and victimization.

Method

Sample

Undergraduate students (257 females, 121 males) at an urban university par- ticipated in an online study for course credit during the academic year. To represent the chronological age of most college students, we limited our sam- ple to those participants between ages 18 and 22 (mean age = 20.0; SD = 1.06). In this sample, 16% of participants identified themselves as Hispanic/ Latino. For self-reported race, 15% endorsed multiple races, 3% African American, 24% Asian, 53% Caucasian, 1% Native Hawaiian/Pacific Islander, and 4% “other” or no response. Because the university Institutional Review Board approved the study as exempt, students read an information sheet and agreed to participate by checking a box. Data were collected anonymously by separating subjects’ identifiers from their data. Based on a subsample for whom we monitored day of participation, all days of the week are represented here without overrepresentation of either weekend or weekdays: 14% Sunday, 16% Monday, 20% Tuesday, 16% Wednesday, 14% Thursday, 12% Friday, and 8% Saturday.

Daily Data

In one sitting, participants completed the online daily questionnaire for 2 consecutive days. They initially were queried on all items for the current day (i.e., “Today”), which is Day 2 in the analyses and results. Participants then completed the entire questionnaire a second time asking them to remember events for the previous day (i.e., “Yesterday”) or Day 1. Instructed to consider friends and dating partners, they responded to 11 items about aggression per- petration (e.g., “said something mean or hurtful in a face-to-face conversa- tion or on the phone”; “pushed, shoved, shook, or grabbed hard”) and the same 11 items for aggression victimization (Cronbach’s α = .77-.85 for

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perpetration and victimization). Several of the items were adapted from an adult measure of intimate partner aggression, the Domestic Conflict Inventory (Margolin, John, & Foo, 1998) but all items were written to be applicable to college friendships and dating relationships; the items included psychologi- cal aggression, electronic aggression, physical aggression, and coerced inti- macy. Participants responded to two additional items assessing alcohol and substance use for each day: “I drank alcohol” and “I used an illegal drug (such as marijuana, cocaine, ecstasy) or prescription drug not prescribed for me.” Of all participants, 27% reported at least 1 day of alcohol consumption, 10% reported at least 1 day of drug use, and 6% endorsed both. Response choices for all aggression and substance use items were on a 3-point Likert- type scale: 0 = not at all, 1 = some, 2 = a lot. In all analyses, the total aggres- sion and substance use variables were treated as ordinal variables with a range of 0 to 2, with 2 representing all scores >2 when summed across sepa- rate items.

Attitudes Justifying Aggression

Attitudes justifying aggression were measured through the 25-item Attitudes about Dating questionnaire (Foo & Margolin, 1995), which assesses wide- ranging circumstances that are sometimes used to “explain” physical aggres- sion in relationships—including humiliation, for example, “makes him/her look like a fool in front of family and friends,” betrayal “learns she/he has been cheating on him/her,” and self-defense, “other person hits him/her first.” Using a 7-point scale (0 = unjustifiable; 6 = justifiable), participants responded to each item twice, once for male-to-female aggression and again for female-to-male aggression (Cronbach’s α = .94-.95).

Results

Bivariate, Proximal Associations Between Substance Use, Aggression Perpetration, and Aggression Victimization

A series of multilevel logistic regressions were used to test bivariate, within- day associations between substance use, perpetration, and victimization. Multilevel models account for statistical dependency that arises from having reports for 2 days from each individual. In the first model, aggression was regressed onto substance use, gender, and the interaction between substance use and gender. Identical models were run with substance use as the outcome and aggression perpetration or victimization as the predictor. Random effects were included on the intercept in all models.

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Significant main effects emerged when predicting aggression from sub- stance use, odds ratio (OR) = 3.27, z = 3.13, p = .002 for perpetration; OR = 5.69, z = 4.09, p < .001 for victimization. For victimization, a significant interaction emerged between substance use and gender, OR = 0.12, z = −2.56, p = .010; decomposition of the interaction showed a significant effect for males, OR = 21.21, p < .001, but not for females, OR = 1.56, p = .15. A paral- lel pattern of significance for males but not females emerged between aggres- sion perpetration and substance use, OR = 8.62, p = .004 for males; OR = 1.24, p = .19 for females, but the interaction between substance use and gen- der did not reach statistical significance, OR = 0.29, z = −1.68, p = .09.

We found a similar pattern of results when predicting substance use from aggression variables. Significant main effects emerged when predicting sub- stance use from aggression perpetration, OR = 2.79, z = 3.16, p = .002, and from aggression victimization, OR = 4.08, z = 4.03, p < .001. There was a significant victimization by gender interaction, OR = 0.19, z = −2.44, p = .015; the association between substance use and victimization was significant for males, OR = 26.0, p < .001, but not for females, OR = 1.66, p = .17. Again, although the association between substance use and aggression perpe- tration was significant for males, OR = 8.53, p = .005, but not for females, OR = 1.52, p = .21, the interaction between perpetration and gender did not reach statistical significance, OR = 0.34, z = −1.70, p = .089.

Conditional Versus Unconditional Probabilities. To further examine the results of the multilevel logistic regressions, Table 1 presents within-day conditional probability tables to examine same day dependencies between aggression and substance use and direction of those dependencies. The probabilities are based on occurrence versus nonoccurrence data with each day entered sepa- rately. The data presented here highlight three comparisons: overall uncondi- tional probabilities, conditional probabilities, and probabilities in the absence of the eliciting condition.

Specifically, males reported aggression perpetration on 33.1% of the days overall but on 51.6% of the days in which they used substances, and on 26.7% of the days in the absence of substance use. Males similarly reported aggres- sion victimization on 32.2% of the total days, but on 58.1% of days they used substances, and 23.3% of days without substance use. Dependencies in the opposite direction show that males reported substance use on 25.6% of the days overall. Males’ substance use increased to 40.0% on the days they reported aggression perpetration (46.2% for aggression victimization) but was 18.5% on days they did not report aggression perpetration (15.9% on days without victimization). Overall, males reported substance use and aggression co-occurrence on 13.2% of days for perpetration and 14.9% of

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days for victimization. Based on both ORs and conditional probabilities, sub- stance use was associated with a greater likelihood of aggression and aggres- sion was associated with a greater likelihood of substance use. Nonetheless, it is still noteworthy that there were more days overall with aggression and no substance use than aggression with substance use (19.8% vs. 13.2% for aggression perpetration; 17.4% vs. 14.9% for aggression victimization).

For females, the nonsignificant findings in the multilevel regressions are evidenced in the similarities between conditional versus unconditional prob- abilities in Table 1. Females’ base-rate for aggression perpetration was 25.5% overall, 30.2% on days with substance use, and 24.5% on days without sub- stance use. In a parallel fashion, females’ base-rate for aggression victimiza- tion was 17.9%, 23.3% on days when they reported substance use, and 16.8% without substance use. Females’ base-rate for substance use was 16.7%, and

Table 1. Within-Day Conditional Probabilities and Base-Rates of Substance Use, and Aggression Perpetration and Victimization.

Aggression Perpetration and Substance Use

Males Females

Any Substance

Use

No Substance

Use Total

Any Substance

Use

No Substance

Use Total

Any aggression perpetration

N (%) 32 (13.2) 48 (19.8) 80 (33.1) 26 (5.1) 105 (20.4) 131 (25.5) Row % (40.0) (60.0) — (19.8) (80.2) — Column % (51.6) (26.7) — (30.2) (24.5) —

No aggression perpetration

N (%) 30 (12.4) 132 (54.5) 162 (66.9) 60 (11.7) 323 (62.8) 383 (74.5) Row % (18.5) (81.5) — (15.7) (84.3) — Column % (48.4) (73.3) — (69.8) (75.5) —

Total (%) 62 (25.6) 180 (74.4) 242 (100) 86 (16.7) 428 (83.3) 514 (100)

Aggression Victimization and Substance Use

Males Females

Any Substance

Use

No Substance

Use Total

Any Substance

Use

No Substance

Use Total

Any aggression victimization

N (%) 36 (14.9) 42 (17.4) 78 (32.2) 20 (4.7) 72 (14.0) 92 (17.9) Row % (46.2) (53.8) — (21.7) (78.3) — Column % (58.1) (23.3) — (23.3) (16.8) —

No aggression victimization

N (%) 26 (10.7) 138 (57.0) 164 (67.8) 66 (12.8) 356 (69.3) 422 (82.1) Row % (15.9) (84.1) — (15.6) (84.4) — Column % (41.9) (76.7) — (76.7) (83.2) —

Total (%) 62 (25.6) 180 (74.4) 242 (100) 86 (16.7) 428 (83.3) 514 (100)

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only 19.8% contingent on aggression perpetration, and 21.7% contingent on aggression victimization. Overall, females’ substance use and aggression per- petration co-occurred on 5.1% of days; substance use and aggression victim- ization co-occurred on 4.7% of days. Females did not show contingencies between substance use and perpetration, or between substance use and vic- timization and reported aggression on more days without than with substance use, 20.4% versus 5.1% for perpetration and 14.0% versus 4.7% for victimization.

Within- and Across-Day Associations Between Substance Use and Aggression

Table 2 displays Spearman rank order correlations for associations involving only the ordinal variables of victimization, perpetration, and substance use (both within and across days), and Pearson correlations for associations involving the continuous variable of attitudes justifying aggression. Aggression perpetration and aggression victimization were significantly cor- related both within and across days for males (all rss > .5) and for females (all rss > .2). Males and females also showed continuity across days for each of the daily variables, for example, Day 1 substance use was correlated with Day 2 substance use, rs = .61 for males and rs = .26 for females. Within-day bivariate associations between substance use and aggression were found for males on both Day 1 and Day 2 (rss range from .25 to .37), but not for females on either day. These gender differences were significant; males, compared to females, showed significantly stronger associations between substance use and victimization (Day 1, z = 2.77, p = .006; Day 2, z = 2.61, p = .009) and between substance use and perpetration (Day 2, z = 3.05, p = .002).

Figure 1 depicts structural equation models (SEM) and standardized parameter estimates to simultaneously examine across-day and within-day associations among victimization, perpetration, and substance use. Consistent with multilevel models and correlation analyses, Day 2 substance use, victim- ization, and perpetration were treated as ordinal variables in all SEM models. The SEM initially was separately estimated for men and women using weighted least square parameter estimates and all like paths were then con- strained in a step-wise fashion to test for gender differences in the strength of each association using multiple group analyses in Mplus, Version 5.21 (Muthén & Muthén, 1998-2007). To allow for estimation of model fit statistics and in light of the similarity for within-day patterns, we only consider Day 2 within-day associations. The final constrained model fit well, χ2 (9) = 9.94, p = .36, CFI = 1.0, RMSEA = .02, and all significant associations were in the

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Table 2. Within-Day and Across-Day Correlations of Daily Variables and Attitudes Condoning Aggression.

Males

1 2 3 4 5 6 7

1. Substance use-Day 1 — 2. Perpetration-Day 1 .25** — 3. Victimization-Day 1 .37**a .76** — 4. Substance use-Day 2 .61** .35** .35** — 5. Perpetration-Day 2 .17 .64** .59** .30**b — 6. Victimization-Day 2 .16 .55** .63** .31**c .73** — 7. Attitudes condoning

male aggression .08 .30** .29** .21* .31** .30** —

8. Attitudes condoning female aggression

.05 .08 .11 .11 .11 .15 .43**

Females

1 2 3 4 5 6 7

1. Substance use-Day 1 — 2. Perpetration-Day 1 .05 — 3. Victimization-Day 1 .08a .46** — 4. Substance use-Day 2 .26** .04 .09 — 5. Perpetration-Day 2 .05 .37*** .34** −.03b — 6. Victimization-Day 2 .01 .23** .42** .03c .51** — 7. Attitudes condoning

male aggression −.05 .02 .08 −.05 .02 .12 —

8. Attitudes condoning female aggression

−.03 .03 .01 .01 .02 .12 .39**

Note: Matching superscripts signify significant differences between males and females. Bolded cells represent within-day correlations.

expected directions. Consistent with correlation results, within-day associa- tions emerged between perpetration and victimization for men and women, and for substance use and both victimization and perpetration for men only (χ2 difference tests revealed that all three within-day associations were signifi- cantly different for men and women at p < .01). Across-day associations revealed consistency over time for all three variables and also showed that males’ and females’ Day 1 victimization related to Day 2 perpetration. In addi- tion, males’ Day 1 perpetration related to Day 2 victimization. None of these associations were significantly different for males and females. Links between substance use and aggression were not found for any across day associations.

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Attitudes Justifying Aggression as a Distal Individual Difference

Overall, female aggression perpetration was rated as more acceptable than male aggression perpetration, F(1,373) = 481.7, p < .001, with no differences for male versus female respondents nor for the interaction between sex of perpetrator and respondent. The mean scores for attitudes justifying males’ aggression were 14.24 (SD = 20.74) for male participants and 12.00 (SD =17.45) for females. For attitudes justifying females’ aggression, means scores were 49.97 (SD = 28.02) for male respondents and 45.34 (SD = 30.36) for females. As seen at the top of Table 2, males’ attitudes condoning male aggression correlated with their own aggression perpetration and victimization on both days (rs range from .29 to .31) and also correlated with Day 2 substance use. Males’ attitudes condoning female aggression did not correlate with any aggression or substance use variables. Females’ attitudes justifying either male or female aggression did not correlate with aggression nor substance use daily variables. Both males and females showed modest correlations between the parallel but separate scales measuring attitudes condoning male and female aggression.

Figure 1. Path model of Day 1 (D1) and Day 2 (D2) substance use, aggression perpetration, and aggression victimization. Note: Matching superscripts signify significant differences between males and females. *p < .05. **p < .01. ***p <.001.

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We then investigated whether attitudes justifying aggression moderated the link between substance use and aggression. We ran multilevel regressions, conducted separately for attitudes condoning male aggression and attitudes condoning female aggression, to predict aggression perpetration and victim- ization with random intercepts included in all models. For males, a significant interaction indicated that attitudes justifying female aggression moderated the association between substance use and males’ violence perpetration, B = .01, p = .048 one-tailed, 95% CI [0.0001, 0.015]. Figure 2 plots mean scores of males’ violence perpetration for groups reporting “no,” “some,” or “high,” substance use for the bottom, middle, and top terciles on attitudes justifying females’ aggression. High aggression perpetration was found for males who reported both substance use and high justification of female aggression. No other interactions for males or females were significant.

Discussion

Despite considerable recognition that both substance use and aggression are serious problems on college campuses, relatively little is known about the extent to which these problems increase the likelihood of each other on the same day. In addressing that gap, the present article shows significant

Figure 2. Mean scores for males’ aggression perpetration as a function of males’ substance use and males’ justification female aggression.

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bidirectional influences in undergraduate males but not females. According to base-rates, males and females, respectively, reported substance use on 25.6% and 16.7% of days, aggression perpetration on 33.1% and 25.5% of days, and aggression victimization on 32.2% and 17.9% of days. On the days that males reported substance use, they also reported a greater than 50% like- lihood of aggression—51.6% for aggression perpetration and 58.1% for aggression victimization. Still, it is noteworthy that the majority of males’ aggression perpetration and victimization occurred in the absence of sub- stance use. For males only, influences also emerged in the opposite direction with aggression perpetration and victimization increasing the likelihood of substance use to 40.0% and 46.2%, respectively. Females, in contrast, did not show within-day links between substance use and aggression. Moreover, sub- stance use and aggression were not linked across the two days of data collec- tion, indicating that proximal influences appear to dissipate over night. Nonetheless, those males and females who engaged in these risky behaviors on the first day were also likely to engage in the same behavior—substance use, aggression perpetration or aggression victimization—on the second day. In addition, males’ endorsement of attitudes justifying male-to-female aggression related to higher aggression perpetration and victimization. Males’ justification of female-to-male aggression also strengthened the link between males’ substance use and aggression perpetration.

The investigation of within-day conditional probabilities provides a unique perspective on temporal dependencies between substance use and aggression. Previous literature provides evidence for time-linked episodes between drinking and intimate partner aggression in college samples (Moore et al., 2011; Parks et al., 2008; Shook et al., 2000) and among those in treat- ment for substance use problems or domestic violence (e.g., Klostermann & Fals-Stewart, 2006). Most of this literature shows that there is heavy drinking prior to episodes of aggression. In a particularly well-designed study, Moore and colleagues collected electronic data through handheld computers each day for 2 months—a method that provided the benefit of daily data over a long duration—and demonstrated increased odds of psychological and physi- cal aggression for drinking versus nondrinking days. Beyond increased odds, it is furthermore important to examine conditional versus unconditional rates of aggression to fully appreciate the risk of initiating and receiving aggres- sion not only among college students who are using substances but also among those who are not using substances.

The present study also investigated effects in the opposite direction—sub- stance use on days when aggression is reported. Our data show that males’ substance use is higher on days when they report aggression perpetration or aggression victimization. Theoretically, this tests a different explanation for

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the link between aggression and substance use, namely that someone might turn to alcohol or other drugs to cope with negative emotions associated with interpersonal aggression (Hines & Douglas, 2012). Although there is some evidence that drinking-to-cope motives (Ham & Hope, 2003) mediate the association between distal victimization and drinking behaviors among col- lege students (e.g., Fossos et al., 2011; Goldstein, Flett, & Wekerle, 2010), little is known about whether coping motives contribute to concurrent daily aggression and substance use. Our results suggest the importance of future research on attitudes endorsing substance use as a possible coping strategy, and investigating whether such attitudes mediate or moderate proximal links between aggression and substance use.

Although the within-day associations show important temporal links, many questions about the sequencing of the substance use and aggression remain unanswered. Substance use and aggression are complex, multifacto- rial behaviors that, in many circumstances, evolve over time. Alcohol intoxication generally increases over several hours; aggressive behaviors typically are embedded in an ongoing argument (Bell & Naugle, 2008); and the two behaviors can mutually intensify and escalate one another. Moreover, other variables, such as stressful events, can precipitate both the substance use and aggression. Thus, within-day associations such as those described here and elsewhere provide support for proximal models but do not directly address causal explanations. Future longitudinal studies that include more detailed assessments of the timing of substance use and aggressive behaviors will allow for better understanding of the dynamic nature of these behaviors over time.

Beyond the sequencing of events, additional details about contextual fac- tors would further inform our understanding of links between aggression and substance use. Shorey and colleagues (2011) note that we may not be able to generalize from adult samples to college samples. We want to emphasize that there also are problems generalizing from college samples to other young adult or later adult samples. Understanding the proximal links between sub- stance use and aggression requires knowledge of these risky behaviors in the context of how college students interact with one another. For example, are college parties a likely context for co-occurrence of substance use and aggres- sion? Alternatively, do students engage in online aggression and threatening text messaging when alone and intoxicated? What is the range of behaviors included in definitions of aggression among college students, particularly with rapid changes in the technology through which college students communicate?

A related consideration with college students is the role of friends versus dating partners. Most previous research on links between aggression and

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substance use has focused exclusively on aggression between dating partners. We, similar to Parks et al. (2008), also examined aggression between friends. This decision reflected previous findings that traditional forms of physical and psychological aggression were comparable between friends and dating partners, and that humiliating forms of electronic aggression actually were more common between friends than dating partners (Bennett, Guran, Ramos, & Margolin, 2011). An important question for a future investigation, how- ever, is whether the same processes underlie proximal links between sub- stance use and aggression with friends and dating partners.

Our data reveal several similarities in males’ and females’ reports of behaviors, and also some important differences. Although not our primary questions here, the consistencies were that: (a) for both males and females, the highest associations were between aggression perpetration and aggres- sion victimization, which is an often-noted finding in college samples (Luthra & Gidycz, 2006; Straus, 2008) although typically referring strictly to dating aggression; and (b) both males and females show associations in the same risk behavior from Day 1 to Day 2. These data support the recent discourse about gender symmetry in rates of intimate partner aggression (Straus, 2009) and dating aggression (Cercone, Beach, & Arias, 2005; Straus & Ramirez, 2007). However, our data also suggest that gender symmetry may not hold with respect to factors contributing to aggression. In our study, only males show links between substance use and aggression. These results support Moore et al. (2011) who reported greater odds for psychological aggression on drinking days for men than for women (7.03 vs. 1.60). Our data for females differ from the Parks et al. (2008) findings of higher violence for female col- lege students on days of substance use and higher substance use following aggression. That previous study, however, selected extreme groups of females for violence history and for heavy drinking whereas the present study did not consider prior history as a condition of selection. In the literature beyond proximal effects, sexual victimization plays an important role in the sub- stance use-aggression links for females (e.g., Walsh et al., 2012). Although our aggression construct included one item about “unwanted sexual contact,” more extensive assessment of sexual aggression and victimization might have strengthened the substance use-aggression associations for females. More generally, in light of the number of studies with only male or female participants, additional direct comparisons between females and males such as those presented here are clearly warranted.

Beyond sex, a number of individual difference variables are emerging as influences in the link between aggression and substance use, including family factors, ethnicity, and personality variables (Caetano et al., 2008; Moore et al., 2011; Reyes et al., 2011; Sullivan et al., 2009). We examined attitudes

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condoning aggression because of their connection to aggressive behaviors (Cauffman et al., 2000; Foo & Margolin, 1995; Schumacher & Slep, 2004) and because of their potential to be modified. We assumed that connections between aggression and substance use would be more pronounced in indi- viduals who hold beliefs that aggression is justified under certain conditions, such as being publicly humiliated. Alternatively, we assumed that those who do not justify aggression would not become aggressive, even under the influ- ence of substances. Males’ justification of male-to-female aggression (a) was associated, in bivariate analyses, with their own aggression perpetration and victimization but (b) did not moderate an already strong connection between male substance use and male aggression perpetration. Somewhat unexpect- edly, however, males who justified female-to-male aggression were more likely to aggress on days when they used substances—perhaps reflecting a nuanced process leading to aggression. It is possible that males who condone aggression in female partners do not extricate themselves from negatively escalating interactions and actually fuel those interactions with their own aggression, particularly when using substances. These data are best viewed as a first pass at the role of attitudes in understanding links between substance use and aggression. The attitudinal measure used here specifically measured justification of dating aggression and thus did not completely match our aggression data that included friends as well as dating partners.

There are several limitations to note. First, because we collected data on only 2 days and because the data were partially retrospective in that the respondent reported on both days at the same time, we were unable to exam- ine certain constructs in more depth. Ideally, with more days of data and with a larger sample size, particularly more males, we could compare models for friends and dating partners to better understand relationship dynamics in the aggression-substance use link. Second, we also combined alcohol and drug use, again due to a limited number of days in which use of either of these substances was reported. That, too, is worthy of future investigation given different psychopharmacologic properties of various substances and recent findings that specific substance disorders are differentially associated with relationship violence (Smith, Homish, Kenneth, & Cornelius, 2011). In addi- tion, we did not assess the substance use quantity. Increasing attention is being directed to links between college binge-drinking and aggression, although data are mixed on whether heavy drinking increases or decreases aggressive behaviors in college males (Moore et al., 2011; Shook et al., 2000). In general, collecting more days of data from more subjects would allow investigation of both between subject and within subject variability and capture more nuanced associations between quantity and type of substance use and severity of aggression. Third, although we intentionally chose to

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investigate these questions within a college sample due to the serious con- cerns about the intersection of these problems on college campuses, we can- not assume that these data generalize beyond a college sample. Moreover, there are further questions to be examined in college samples, for example, do links between alcohol and aggression vary across the college years or predict behaviors following college? Fourth, because these results derive from self-report data, it is possible that aggression is underreported; collect- ing data directly from friends or romantic partners might reveal additional instances of participants’ aggression. Finally, our data also do not investigate another dimension in the substance use-aggression link, that is, whether sub- stance use by friends or romantic partners underlies the participants’ aggres- sion victimization or their aggression perpetration.

Despite these limitations, major strengths of the study are the investiga- tion of bidirectional influences between substance use and aggression and the use of daily data, which allow for temporal explanations. Daily data also require much shorter recall and are considered to be more reflective of daily life experiences than retrospective questionnaires that sum over a month or year (Bolger, Davis, & Rafaeli, 2003). The assessment of within and across day links, the inclusion of both perpetration and victimization, and direct comparisons between males and females further contribute to what is known about the co-occurrence of substance use and aggression in college students.

Summary

Our results document significant bidirectional within-day influences between males’ substance use and their aggression perpetration and aggression vic- timization, and also show that attitudes justifying aggression can strengthen the link between substance use and males’ aggression perpetration. Not to overstate such connections, these data also illustrate that considerable aggres- sion involving both males and females occurs in the absence of substance use. Nonetheless, further accounting of associations between substance use and aggression in college students is recommended given the high rates and serious consequences of these problems on college campuses. Moreover, as college campuses continue to launch new initiatives to address the harms associated with substance use, particularly alcohol intoxication (Paschall, Antin, Ringwalt, & Saltz, 2011), attention to aggression perpetration and vic- timization is warranted. Likewise, interventions focused on dating violence should address the link with substance use (Roudsari, Leahy, & Walters, 2009; Shorey et al., 2011). Interventions that take a more integrated approach and that aim to weaken the link between substance use and aggression can benefit both males and females—from the perspective of being self-aware of

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bidirectional influences in one’s own behavior as well as being cognizant of the potential harms associated with the actions of friends and romantic partners.

Acknowledgment

We appreciate the contributions of Kelly Young-Wolff and members of the USC Family Studies Project.

Declaration of Conflicting Interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research was supported by the National Institutes of Health, Eunice Kennedy Shriver National Institute of Child Health and Human Development [Grant R01 HD046807 awarded to Margolin, Grant NRSA F32 HD060410 awarded to Baucom] and by the University of Southern California (USC) Dana and David Dornsife College of Letters, Arts, and Sciences Research Award to Margolin and Ramos.

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Author Biographies

Gayla Margolin is professor of Psychology and Pediatrics at the University of Southern California. She investigates the intergenerational continuity of aggression from adolescents’ experiences in their family of origin to their friendships and dating relationships during young adulthood. Her recent publications identify individual and family factors that contribute to adolescents’ behavioral and health risks. Her work has been supported by NICHD (R01 HD046807) and previously has been funded by NIMH and the Lucile Packard Foundation.

Michelle C. Ramos is a research associate in the Department of Psychology at the University of Southern California. Her research focuses on the effects of family stress and violence on youth adjustment, and the impact of family aggression on youths’ own romantic relationships. She is also particularly interested in using prospective data collected on a daily basis and detailed observational data to examine family pro- cesses and interactions.

Brian R. Baucom is an assistant professor of Psychology at the University of Utah. He recently completed a Postdoctoral Fellowship in the Department of Psychology at the University of Southern California funded by a NIH Ruth L. Kirschstein National Research Service Award to investigate the impact of family aggression on emotional processes during family interaction (F32 HD060410). He is an expert on dysfunc- tional styles of couple and family interaction and behavioral couple therapy. He also has expertise in statistical methods for complex nested designs such as mixed effects models for regression and structural equation modeling.

Diana C. Bennett is presently a PhD student in clinical psychology at the University of Utah, where she is working with Dr. Patricia Kerig to investigate the links between trauma and delinquency in juvenile justice-involved youth. She completed her BA in

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psychology at the University of Southern California, where she worked as the project coordinator and a research assistant to the USC Family Studies Project.

Elyse L. Guran is a project manager with the USC Family Studies Project at USC. She recently completed a postbaccalaureate premedical student at Bryn Mawr College. She graduated from the University of Southern California with a degree in Psychology. She received a NIH-NICHD postbaccalaureate research fellowship and has been involved with the Family Studies Project for over 5 years.