Who is sexually faithful? Own and partner personality traits as predictors of infidelity

Abstract

Infidelity can have harmful consequences for all those involved. Although prior research has demonstrated some reliable associations between certain personality traits and infidelity, the associations between other personality traits and infidelity are less clear. Moreover, prior research has been limited in addressing the role of partner personality and whether any effects are independent of relationship satisfaction. Thus, we pooled data from two 3-year longitudinal studies of newlywed couples to examine the associations between both couple members’ personality (Big Five and narcissism) and infidelity, controlling and not controlling for marital satisfaction. Wives high (versus low) in extraversion and husbands and wives with partners high (versus low) in neuroticism or extraversion were more likely to engage in infidelity regardless of whether we controlled for satisfaction. Husbands with partners high (versus low) in narcissism were more likely to engage in infidelity, though this effect was no longer significant when controlling for satisfaction. These findings demonstrate that even predicting a behavior as self-oriented as infidelity requires considering the qualities of both couple members, highlighting the importance of adopting a dyadic approach to relationships.

Keywords

Big five infidelity marriage narcissism personality

From Hester Prynne to Tiger Woods, the perils of being unfaithful are well documented. Indeed, empirical evidence demonstrates severe consequences of infidelity for long-term relationships. Following incidences of infidelity, both partners report lower relationship satisfaction, and marriages characterized by infidelity are nearly twice as likely to end in divorce (Previti & Amato, 2004). In fact, infidelity is the most common predictor of relationship dissolution across more than 150 societies (Betzig, 1989; see Fincham & May, 2017). Yet, numerous people report engaging in an infidelity at least once (Atkins & Kessel, 2008). In light of the harmful consequences, it is important to understand predictors of infidelity.

According to interdependence theory (Kelley & Thibaut, 1978), the behaviors and outcomes of relationship partners are inextricably intertwined, and theoretical advances (e.g., Karney & Bradbury, 1995; Zayas, Shoda, & Ayduk, 2002) posit that both partners’ enduring characteristics are critical to predicting relationship processes and outcomes. Indeed, a robust body of work indicates that the personality traits of both partners play a critical role in shaping various relationship processes (Karney & Bradbury, 1995; Kelly & Conley, 1987; Roberts, Kuncel, Shiner, Caspi, & Goldberg, 2007; for a review, see McNulty, 2013), including sexual processes (Fisher & McNulty, 2008; McNulty & Widman, 2013, 2014; Meltzer & McNulty, 2016). The goal of the current study was to explore the implications of both intimates’ personality traits for infidelity in the context of marriage.

Own personality and infidelity

According to Karney and Bradbury’s (1995) vulnerability–stress–adaptation model of marriage, both partners bring to their relationship their own set of enduring characteristics that predispose them to various adaptive and maladaptive interpersonal processes. One of the more significant of these is their personality, which captures a host of individual differences in responding. According to several theoretical and empirical traditions, the five-factor model of personality (consisting of neuroticism, agreeableness, conscientiousness, extraversion, and openness to experience) captures all, or at least most, facets of personality (McCrae & Costa, 1997). Indeed, within relationship science, there is robust evidence suggesting that people’s Big Five traits are associated with infidelity (e.g., Barta & Kiene, 2005; Buss & Shackelford, 1997; Orzeck & Lung, 2005; Schmitt, 2004; Schmitt & Buss, 2001; Schmitt & Shackelford, 2008). Nevertheless, considerable variability exists in the reliability of the associations that have been established.

The three traits most reliably linked to infidelity are neuroticism (characterized by emotional instability and worry), agreeableness (characterized by kindness and trustworthiness), and conscientiousness (characterized by self-discipline and reliability). Individuals high (versus low) in neuroticism are more likely to report having engaged in infidelity in their previous relationships (Barta & Kiene, 2005; Schmitt & Buss, 2001) and in their current marriages (Whisman, Gordon, & Chatav, 2007), although some research suggests such effects are stronger among women (Schmitt & Shackelford, 2008). In contrast, individuals high (versus low) in agreeableness or conscientiousness describe themselves as more faithful (Schmitt, 2004), are less likely to report having engaged in infidelity (Barta & Kiene, 2005; Orzeck & Lung, 2005; Schmitt & Buss, 2001), and report a lower likelihood of engaging in future infidelity (Buss & Shackelford, 1997).

Results have been more mixed with respect to the associations between infidelity and the other two factors: openness (characterized by curiosity and imaginativeness) and extraversion (characterized by assertiveness and gregariousness). Some studies demonstrate a positive association between intimates’ openness and infidelity (Buss & Shackelford, 1997; Orzeck & Lung, 2005), other findings demonstrate a negative association between openness and perceived likelihood of infidelity (Schmitt, 2004) as well as between openness and retrospective reports of infidelity (particularly among men; Schmitt & Shackelford, 2008), and still other studies suggest that openness is unassociated with infidelity (Barta & Kiene, 2005; Schmitt & Buss, 2001). Likewise, some studies demonstrate a positive association between extraversion and the likelihood of infidelity (Buss & Shackelford, 1997; Schmitt, 2004) as well as between extraversion and retrospective reports of infidelity (Orzeck & Lung, 2005; Schmitt & Shackelford, 2008) whereas other studies suggest that extraversion is unassociated with infidelity (Barta & Kiene, 2005; Schmitt & Buss, 2001).

Although the Big Five presumably account for the majority of variability in personality, a separate literature has explored the association between infidelity and another relevant personality factor—narcissism (characterized by feelings of superiority and low empathy; Campbell, Foster, & Finkel, 2002; Raskin & Terry, 1988). According to that research, narcissism is also associated with an increased risk of infidelity. Specifically, people high (versus low) in narcissism report more permissive attitudes toward engaging in infidelity (Hunyady, Josephs, & Jost, 2008) and a greater likelihood of engaging in concurrent (Atkins, Yi, Baucom, & Christensen, 2005; Campbell et al., 2002) and future infidelity (Buss & Shackelford, 1997). As far as we are aware, however, no research has examined whether these effects are independent of the Big Five.

Partner personality and infidelity

As noted, relationships are inherently interdependent (Kelley & Thibaut, 1978), such that one partner’s behavior is difficult, if not impossible, to understand without considering aspects of the other partner. With respect to the partner’s personality in particular, Zayas, Shoda, and Ayduk (2002) drew on a broad tradition of research examining the role of situational factors in the link between personality and behavior to note that partner personality is a powerful situational factor that predicts behavior; that is, people’s behaviors depend not only on their own personality but also on their partner’s personality. Yet, research examining the associations between partner personality and infidelity is even more limited and inconsistent. For example, Buss and Shackelford (1997) demonstrated that whereas partner neuroticism is positively associated and partner conscientiousness is negatively associated with men’s (but not women’s) reported likelihood of engaging in future infidelity, partner agreeableness, openness, and extraversion are unassociated with people’s likelihood of engaging in future infidelity. Moreover, although Shackelford, Besser, and Goetz (2008) demonstrated a similar negative association between perceived likelihood of own infidelity and partner conscientiousness, they also demonstrated a negative association between perceived likelihood of own infidelity and partner agreeableness. Finally, Orzeck and Lung (2005) demonstrated that individuals who retrospectively reported having engaged (versus not engaged) in infidelity rated their partners lower on all Big Five personality traits.

Partner narcissism, in contrast, has been more consistently associated with measures of infidelity. Specifically, people high (versus low) in narcissism are more likely to report being the victims of infidelity (Hunyady et al., 2008) and partner narcissism is positively associated with women’s (but not men’s) reported likelihood of engaging in future infidelity (Buss & Shackelford, 1997).

Moving forward

Given these inconsistences, additional methodologically sound research is necessary to build a more informative literature, and there are several methods that may be particularly likely to do so. First, research may benefit from examining the influence of both partners’ personality traits simultaneously. Given that both partners play a role in shaping relationships (Kelley & Thibaut, 1978), and given that such traits may be associated, isolating the effects of each couple member’s personality requires simultaneously accounting for both partners’ personality (see McNulty, 2013). Further, due to biases in people’s perceptions of others (Jones & Nisbett, 1972), it would be ideal to obtain both partners’ self-reported personality. Here, we simultaneously examined the associations between both partners’ self-reported personality and infidelity.

Second, research may benefit from a stronger operationalization of infidelity (see Fincham & May, 2017). Infidelity has been operationalized different ways across prior studies, including perceptions of one’s own and one’s partner’s likelihood of future infidelity (Buss & Shackelford, 1997), faithfulness (Schmitt, 2004), and reports of actual infidelity (Orzeck & Lung, 2005). Here, we asked participants to report on actual infidelity and cast a wide net by assessing both partners’ reports.

Third, research has tended to ignore the potential role of relationship satisfaction in the association between personality and infidelity (see Fincham & May, 2017). A robust literature, however, demonstrates that various aspects of both partners’ personality are associated with lower levels of satisfaction (Malouff, Thorsteinsson, Schutte, Bhullar, & Rooke, 2010; McNulty, 2013). Such associations may create an interpersonal context that makes infidelity more or less likely, and knowing whether associations between personality and infidelity emerge independent of satisfaction can provide insights into the processes through which personality predicts infidelity.

Lastly, research may benefit from using large samples, perhaps drawing from multiple studies, to (a) enhance power and (b) provide the opportunity to test whether any associations are robust across studies. Indeed, using small samples can increase both Type I and Type II error rates (see Finkel, Eastwick, & Reis, 2015).

Overview of the current research

In light of these issues, we used data from two longitudinal studies of newlywed couples to examine the associations between both partners’ self-reported personality and infidelity (see Online Supplementary Materials for other published articles that have used these data). According to interdependence theory (Kelley & Thibaut, 1978) and recent theoretical perspectives on the role of both partners’ personality (Karney & Bradbury, 1995; Zayas et al., 2002), both partners’ personality likely influences whether people engage in infidelity. Thus, in each study, we assessed each spouse’s Big Five personality traits, narcissism, marital satisfaction, and infidelity at the start of marriage. Then, across the subsequent 3 years, we assessed spouses’ infidelity and satisfaction every 6 months (Study 1) or yearly (Study 2). Due to their similar designs, we describe both studies simultaneously and analyzed them together, though we controlled and tested for idiosyncratic differences across studies.

Method

Participants

Participants in Study 1 were 216 members of 108 couples participating in a broader longitudinal study of 113 heterosexual couples. Participants in Study 2 were 238 members of 119 couples participating in a broader longitudinal study of 120 couples (119 heterosexual couples; 1 lesbian couple). On average, husbands and wives at baseline were 30.33 (SD = 8.29) and 28.61 (SD = 6.88) years of age, respectively. Recruitment strategies and additional sample characteristics appear in the Online Supplementary Materials.

As part of the broader study goals, eligibility required that all participants (a) had been married less than 4 months in Study 1 and less than 3 months in Study 2, (b) spoke English (to ensure questionnaire comprehension), and (c) were at least 18 years of age. Study 1 included the additional criterion that both partners were in their first marriage.

Procedure

After enrolling in each study, participants were either mailed a packet of surveys to complete at home and bring with them to a laboratory session or emailed a link to Qualtrics.com, where they completed the surveys online prior to their session. These surveys included a consent form approved by the local human subjects review board; measures assessing their Big Five, narcissism, marital satisfaction, and infidelity; additional measures beyond the scope of these analyses; and a letter instructing spouses to complete their questionnaires independently of one another. We compensated couples US$100 for completing the surveys and corresponding laboratory session. During the subsequent 3 years, we recontacted couples at approximately 6-month (Study 1) and 1-year (Study 2) intervals and again mailed measures assessing infidelity and satisfaction, along with a letter of instruction reminding participants to complete their forms independently. Couples received a check (Study 1 = US$30; Study 2 = US$25) for completing each follow-up. The minor differences in procedures across the studies were due to broader aims of each study and constraints on each investigator, which we statistically controlled with a dummy code (Study 1 = 0, Study 2 = 1).

Measures

Big Five personality

At baseline, we assessed participants’ Big Five personality traits using the International Personality Item Pool (Goldberg, 1999). In Study 1, we assessed neuroticism and conscientiousness using the 60-item subscales, and we assessed extraversion, openness, and agreeableness using the 10-item subscales. In Study 2, we assessed all five traits using the 60-item subscales. Differences in the number of items used within and across studies were due to the goals of the broader studies and attempts to minimize participant burden. For each item across all subscales, participants indicated the extent to which different statements accurately described them using a five-point scale, where 1 = very inaccurate and 5 = very accurate. We averaged items across each subscale to form measures of each spouse’s Big Five. Internal consistency was high across all subscales in both studies (all αs ≥ .84).

Narcissism

At baseline, we assessed narcissism using the forced-choice version of the 40-item Narcissistic Personality Inventory (NPI; Raskin & Terry, 1988). This version of the NPI asks participants to agree or disagree with each item using a yes–no response format. We computed scores for each spouse by averaging endorsements, or yes responses, across items; scores closer to 1 indicate higher narcissism. Internal consistency was high (in both studies, α = .87).

Infidelity

At baseline and each follow-up, intimates reported on their own and their partner’s infidelity. Specifically, intimates in Study 1 reported whether they “had sexual relations with anyone other than [their] spouse over the past 6 months” and whether their “spouse had sexual relations with anyone other than [them] over the past 6 months.” Intimates in Study 2 reported whether they “had a romantic affair/infidelity” and whether they “learned that [their] spouse had a romantic affair/infidelity.”¹ In both studies, we used responses to both questions at all assessments to form a dummy code indicating whether each participant engaged in at least one infidelity over the course of the study according to either their own or their partner’s report (0 = no infidelity, 1 = infidelity).² A total of 35 (7.7%) intimates (23 husbands and 12 wives) engaged in infidelity that was reported by at least one couple member during at least one assessment. Nine of these infidelities were reported by both couple members³; the remaining 26 cases were fairly evenly split between participant-reported infidelity (n = 11) and partner-reported infidelity (n = 15). As Fincham and May (2017) recently argued, methodological inconsistencies such as these are “understandable in researching a phenomenon that is rooted in deceit and thus inimical to the truth that science seeks to illuminate” (p. 73). We chose to use both reports to form our index of infidelity because we assumed there was more signal than noise in each person’s report. Notably, supplementary analyses using self- and partner-reported infidelity separately demonstrate a largely similar pattern of results (see Online Supplementary Materials).

Covariate

To ensure that any effects were not due simply to lower levels of own or partner marital satisfaction (see Fincham & May, 2017), intimates completed a measure of global marital satisfaction at baseline and each follow-up. Specifically, participants completed the Quality Marriage Index (Norton, 1983). We averaged participants’ scores across assessments to form indexes of own and partner average marital satisfaction. Internal consistency was high across all assessments in both studies (all αs ≥ .92).

Results

Descriptive statistics and correlations of all predictors appear in Table 1. Given the nonindependent nature of the couple-level data, we estimated a multilevel model to examine the associations between both partners’ personality and infidelity. Specifically, we estimated a two-level model that regressed concurrent and prospective infidelity onto participants’ own personality traits (standardized and entered uncentered) and their partners’ personality traits (standardized and entered uncentered) simultaneously (12 traits in total) at Level 1, controlling for study (grand-mean centered) at the Level-2 intercept. We allowed the Level-2 intercept to vary randomly across couples and specified a Bernoulli sampling distribution due to the dichotomous nature of infidelity. To provide the most information and help readers interpret these results in light of existing research that shows sex-differentiated effects, we estimated this model three times: once allowing each predictor to interact with a dummy variable with husbands coded 0 to obtain husbands’ simple effects, once allowing each predictor to interact with a dummy variable with wives coded 0 to obtain wives’ simple effects, and once collapsing across sex for effects not moderated by participant sex. Further, we report (a) univariate associations between personality and infidelity—several that replicated actor effects found in previous research, (b) multivariate associations between own personality and infidelity, and (c) multivariate associations between partner personality and infidelity in the Online Supplementary Materials.

Table 1.
Descriptive statistics of and correlations between husbands’ and wives’ personality and baseline marital satisfaction.

Husbands Wives

(1) (2) (3) (4) (5) (6) (7) M SD M SD

(1) Neuroticism .11 −.42* −.23* −.38* −.17 −.18 −.21 2.24 _a 0.58 2.55 _b 0.61

(2) Conscientiousness −.34* .06 .33* .30* .25* .29* .18 3.89 _a 0.50 4.04 _b 0.48

(3) Agreeableness −.17* .44*** .16* .28* .27* −.06 .05 3.74 _a 0.55 4.01 _b 0.56

(4) Extraversion −.24*** .16* .08 .06 .25* .44* .07 3.39 _a 0.69 3.33 _a 0.70

(5) Openness −.13^† .23 .39* .24*** .09 .14* .10 3.73 _a 0.57 3.73 _a 0.57

(6) Narcissism −.00 .05 −.20 .35* .02 .31* .01 0.51 _a 0.18 0.47 _b 0.17

(7) Marital satisfaction −.29* .15* −.03 .18 .02 −.05 .54* 41.74 _a 4.66 41.91 _a 4.24

Note. Husbands’ correlations appear above the diagonal and wives’ correlations appear below the diagonal. Correlations between spouses are presented in bold along the diagonal. Means in the same row with different subscripts differ at p < .05. For husbands, N = 226; for wives, N = 228.

^† p < .10; p < .05; p < .01; p < .001.

Results from the primary analyses are presented in Table 2. As can be seen, the associations between (a) extraversion and infidelity and (b) partner narcissism and infidelity differed across spouses’ sex. Wives high (versus low) in extraversion and husbands with partners high (versus low) in narcissism were more likely to engage in infidelity during the first 3 years of marriage; extraversion was unassociated with husbands’ infidelity and partner narcissism was unassociated with wives’ infidelity. Collapsing across spouses’ sex, intimates with partners high (versus low) in neuroticism or extraversion were more likely to engage in infidelity during the first 3 years of marriage. Importantly, these associations represent the unique influence of each personality trait, above and beyond the influence of all other own and partner personality traits.

Table 2.
Associations between personality and infidelity, controlling for study.

Husbands’ infidelity Wives’ infidelity Sex difference Infidelity

β SE r β SE r p β SE r

Intercept −2.59* 0.24 – −3.00* 0.27 – .235 −2.87* 0.17 –

Study 0.81^† 0.42 .13 0.37 0.49 .05 .442 0.62^† 0.35 .12

Own extraversion −0.28 0.32 .06 0.77 0.29 .18 .016* – – –

Own agreeableness −0.16 0.24 .05 −0.38 0.44 .06 .664 −0.22 0.20 .08

Own conscientiousness −0.10 0.20 .03 −0.00 0.21 .00 .762 −0.12 0.16 .05

Own openness 0.19 0.17 .08 0.12 0.26 .03 .825 0.16 0.13 .08

Own neuroticism 0.08 0.19 .03 −0.18 0.21 .06 .357 −0.02 0.14 .01

Own narcissism −0.06 0.22 .02 0.35 0.31 .08 .323 0.09 0.18 .03

Partner extraversion 0.35 0.21 .12 0.37^† 0.20 .13 .940 0.34^* 0.16 .14

Partner agreeableness 0.23 0.24 .07 0.06 0.43 .01 .730 0.14 0.20 .05

Partner conscientiousness 0.01 0.24 .00 0.52^† 0.27 .14 .146 0.19 0.18 .07

Partner openness −0.36* 0.16 .15 0.05 0.24 .01 .168 −0.19 0.14 .10

Partner neuroticism 0.56 0.16 .24 0.79 0.24 .23 .429 0.62*** 0.14 .28

Partner narcissism 0.49* 0.23 .15 −0.27 0.24 .08 .035* – – –

Note. For intercept and study estimates, df = 225; for all other variables, df = 201, in the models examining simple effects within sex, and, df = 212, in the model that collapses across sex. Sex differences represent tests of Variable × Sex interactions. Effect size r is reported. All coefficients can be converted into probabilities by taking the exponent of the probabilities. For study, Study 1 = 0, Study 2 = 1.

^† p < .10; p < .05; p < .01; p < .001.

We conducted three sets of supplemental analyses. First, we examined whether own or partner marital satisfaction accounted for any effects; only the association between partner narcissism and husbands’ infidelity became nonsignificant when we controlled for own or partner satisfaction. Follow-up analyses using RMediation (Tofighi & MacKinnon, 2011) indicated that own satisfaction did not mediate this association, β = .09, CI_95% [−.01, .22], though partner satisfaction did mediate this association, β = .16, CI_95% [.002, .332]. In other words, partner narcissism was indirectly associated with husbands’ infidelity through their partners’ lower satisfaction. Second, we examined whether own or partner satisfaction moderated any significant associations; neither did (all ps ≥ .192). Finally we examined whether study moderated any significant associations; study moderated the partner neuroticism effect, β = 0.72, t(205) = 2.20, p = .029, effect size r = .15, such that the effect emerged in Study 2, β = 0.91, t(205) = 4.89, p < .001, effect size r = .32, but not in Study 1, β = 0.19, t(205) = 0.72, ns.

Discussion

We pooled data from two longitudinal studies of newlywed couples to examine the unique associations between own and partner personality and infidelity across the first 3 years of marriage. Although husbands’ own personality traits were unassociated with their infidelity, wives high (versus low) in extraversion were more likely to engage in infidelity. Moreover, spouses with partners high (versus low) in neuroticism or extraversion were more likely to engage in infidelity, and husbands with partners high (versus low) in narcissism were more likely to engage in infidelity. Notably, these effects represent unique associations, above and beyond the influence of all other own and partner personality traits. All effects remained significant controlling for own and partner marital satisfaction, except the effect of partner narcissism among husbands—which was mediated by partner marital satisfaction.

Several factors limit interpretations of the current findings until they can be replicated and extended. First, the relative homogeneity limits our ability to generalize these findings to other samples (e.g., older married couples). Indeed, as Fincham and May (2017) suggest, infidelity research should be interpreted with caution prior to replication using representative samples. Second, researching a sensitive or socially taboo behavior such as infidelity is complicated by a myriad of issues (e.g., secrecy, shame, social desirability; Blow & Hartnett, 2005; Krumpal, 2013; see Fincham & May, 2017). These issues likely inhibit individuals’ willingness to report such behaviors, despite the steps we took to increase confidentiality. We attempted to minimize measurement problems by assuming infidelities reported by either partner were in fact infidelities, regardless of whether they were mutually reported. Although supplemental analyses demonstrated similar patterns using self- and partner-reported infidelities separately, there remains the possibility that some partner reports reflect (false) suspicions of infidelity. Future research should address this possibility. Additionally, our operationalization of infidelity, particularly in Study 1, may have confounded consensual nonmonogamy with infidelity. Nevertheless, given the low prevalence of consensually nonmonogamous relationships (Conley, Moors, Matsick, & Zeigler, 2013; Rubin, Moors, Matsick, Ziegler, & Conley, 2014), and given that similar findings emerged in Study 2 alone (which operationalized infidelity in terms of unfaithfulness; see Online Supplementary Materials), it is unlikely that the associations we observed here are driven by such relationships. Of course, future research may benefit from directly addressing this possibility. Third, although we obtained prospective reports of infidelity at follow-up assessments, spouses also reported recent infidelity at baseline. It is possible that personality is associated with self-reporting bias or memory bias of past infidelity. This assessment of infidelity, however, assessed behavior across the prior 6 (Study 1) and 4 (Study 2) months, helping to reduce such bias. Fourth, the data examined here are correlational and thus cannot support strong causal conclusions. Although we were able to estimate the effects of both partners’ personality simultaneously controlling for marital satisfaction, we did not control for other potential third variables. Finally, our observed effects were relatively small in magnitude. Romantic relationships are inherently complicated, and numerous factors contribute to relationship outcomes and behaviors (Karney & Bradbury, 1995; Le, Dove, Agnew, Korn, & Mutso, 2010), including the likelihood of engaging in an infidelity.

These limitations notwithstanding, the current study has important implications. Most notably, these findings join a large body of empirical evidence that provides support for theoretical perspectives espousing the importance of partners’ personality to relationship behavior (Kelley & Thibaut, 1978; Zayas et al., 2002). Although, the current study demonstrated that a major component of people’s own enduring characteristics—their personality—was largely unassociated with whether they engaged in infidelity, these findings underscore the integral role that partners’ enduring characteristics play in influencing people’s own relationship behaviors. Indeed, with the exception of wives’ own extraversion, only partner personality was associated with infidelity across the first several years of marriage. Notably, most of the associations between own personality and infidelity demonstrated in prior research did not emerge in the current study. This may be due, in part, to our data analytic strategy that simultaneously estimated unique associations among both couple members’ Big Five and narcissism; most previous research has examined bivariate correlations between each individual personality trait and infidelity (Buss & Shackelford, 1997; Schmitt, 2004; Schmitt & Buss, 2001; Schmitt & Shackelford, 2008) or conducted series of analyses of variance to compare personality traits between faithful and unfaithful participants (Barta & Kiene, 2005; Orzeck & Lung, 2005). Indeed, it is worth noting that we replicated many of these actor effects when we analyzed our data in this manner (see Online Supplementary Materials). Nevertheless, these actor effects disappeared when we simultaneously accounted for partner personality traits. In this way, the current findings suggest that infidelity may be better explained by partner (versus own) personality. Given that people’s own enduring characteristics and their partners’ enduring characteristics influence their shared environment, it is possible that people’s partners’ personality traits, specifically, influence the negativity of their shared environment to a greater extent than do people’s own personality traits. Nevertheless, in light of the low probability of infidelities reported in these studies and the inconsistencies observed in prior research, future research would benefit from further exploring the role that partner personality plays in predicting infidelity.

It is also worth emphasizing, however, that the positive association that emerged between wives’ extraversion and their own infidelity did replicate prior research (Buss & Shackelford, 1997; Orzeck & Lung, 2005; Schmitt, 2004; Schmitt & Shackelford, 2008), as did the positive association that emerged between partner neuroticism and infidelity (Buss & Shackelford, 1997). The association between partner narcissism and husbands’ infidelity was consistent with some research (Hunyady et al., 2008) but inconsistent with other research showing such an association only among women (Buss & Shackelford, 1997). Here, we demonstrated that these associations emerged independent of other personality traits and that the associations involving wives’ extraversion, partner extraversion, and partner neuroticism emerged independent of relationship satisfaction.

Future research should examine potential mechanisms that might explain the associations between personality and infidelity. Although the current research demonstrated that partner relationship satisfaction mediated the association between partner narcissism and husbands’ infidelity, we were unable to account for other associations that emerged. For example, given that neuroticism is associated with less frequent in-pair sex and lower sexual satisfaction (Costa, Fagan, Piedmont, Ponticas, & Wise, 1992; Fisher & McNulty, 2008; Meltzer & McNulty, 2016), which are themselves associated with extra-pair sex (Liu, 2000; Yucel & Gassanov, 2010), it is possible that sexual satisfaction mediates the association between partner neuroticism and infidelity. Likewise, given that extraversion may be associated with greater attention to alternative partners, which is associated with less commitment (Maner, Gailliot, & Miller, 2009), attention or access to alternatives may explain the association between own and partner extraversion and infidelity. Finally, although personality remains somewhat stable over time (Costa & McCrae, 1988), it is possible that infidelity influences personality. Indeed, research has demonstrated that personality can change over time, and such changes are associated with people’s life experiences including marriage (Mroczek & Spiro, 2003; Roberts & Mroczek, 2008). Although we were unable to assess this in the current study (we only assessed personality at baseline), future research may benefit from doing so. Finally, in light of other research highlighting the role of sexual narcissism (i.e., narcissistic qualities specifically activated in the sexual domain) in predicting infidelity and other sexual outcomes more reliably than globally assessed narcissism (McNulty & Widman, 2013, 2014), research may benefit from examining whether other personality characteristics better predict infidelity when assessed with specific reference to the sexual domain.

Conclusion

The current research highlights the importance of adopting a dyadic perspective to understanding relationships—even a self-oriented behavior such as engaging in sexual relationships with alternative partners depends on not only those actors’ personalities but also their partners’ personalities. In fact, among newly married couples—dyads assumed to be quite satisfied, partner characteristics uniquely explain who is most likely to be unfaithful. That is, the dyadic effects observed here suggest that understanding who is most at risk for infidelity requires considering both partners’ personality characteristics.

Supplementary Material

Supplemental Material, jspr-17-173-File003 - Who is sexually faithful? Own and partner personality traits as predictors of infidelity

Supplemental Material, jspr-17-173-File003 for Who is sexually faithful? Own and partner personality traits as predictors of infidelity by Emma E. Altgelt, Melanie A. Reyes, Juliana E. French, Andrea L. Meltzer, and James K. McNulty in Journal of Social and Personal Relationships

								Husbands	Wives
(1) Neuroticism	.11	−.42***	−.23***	−.38***	−.17**	−.18**	−.21**	2.24 _a	0.58	2.55 _b	0.61
(2) Conscientiousness	−.34***	.06	.33***	.30***	.25***	.29***	.18**	3.89 _a	0.50	4.04 _b	0.48
(3) Agreeableness	−.17*	.44***	.16*	.28***	.27***	−.06	.05	3.74 _a	0.55	4.01 _b	0.56
(4) Extraversion	−.24***	.16*	.08	.06	.25***	.44***	.07	3.39 _a	0.69	3.33 _a	0.70
(5) Openness	−.13^†	.23**	.39***	.24***	.09	.14*	.10	3.73 _a	0.57	3.73 _a	0.57
(6) Narcissism	−.00	.05	−.20**	.35***	.02	.31***	.01	0.51 _a	0.18	0.47 _b	0.17
(7) Marital satisfaction	−.29***	.15*	−.03	.18**	.02	−.05	.54***	41.74 _a	4.66	41.91 _a	4.24

	Husbands’ infidelity	Wives’ infidelity	Sex difference	Infidelity
Intercept	−2.59***	0.24	–	−3.00***	0.27	–	.235	−2.87***	0.17	–
Study	0.81^†	0.42	.13	0.37	0.49	.05	.442	0.62^†	0.35	.12
Own extraversion	−0.28	0.32	.06	0.77**	0.29	.18	.016*	–	–	–
Own agreeableness	−0.16	0.24	.05	−0.38	0.44	.06	.664	−0.22	0.20	.08
Own conscientiousness	−0.10	0.20	.03	−0.00	0.21	.00	.762	−0.12	0.16	.05
Own openness	0.19	0.17	.08	0.12	0.26	.03	.825	0.16	0.13	.08
Own neuroticism	0.08	0.19	.03	−0.18	0.21	.06	.357	−0.02	0.14	.01
Own narcissism	−0.06	0.22	.02	0.35	0.31	.08	.323	0.09	0.18	.03
Partner extraversion	0.35	0.21	.12	0.37^†	0.20	.13	.940	0.34^*	0.16	.14
Partner agreeableness	0.23	0.24	.07	0.06	0.43	.01	.730	0.14	0.20	.05
Partner conscientiousness	0.01	0.24	.00	0.52^†	0.27	.14	.146	0.19	0.18	.07
Partner openness	−0.36*	0.16	.15	0.05	0.24	.01	.168	−0.19	0.14	.10
Partner neuroticism	0.56**	0.16	.24	0.79**	0.24	.23	.429	0.62***	0.14	.28
Partner narcissism	0.49*	0.23	.15	−0.27	0.24	.08	.035*	–	–	–

Footnotes

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Preparation for this article was partially funded by a National Science Foundation Grant (BCS-1251520) awarded to James K. McNulty (Study 2).

Supplementary material

Supplementary material for this article is available online.

Notes

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