Something s Missing: Need Fulfillment and Self-Expansion as Predictors of Susceptibility to Infidelity

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1 The Journal of Social Psychology, 2006, 146(4), Copyright 2006 Heldref Publications Something s Missing: Need Fulfillment and Self-Expansion as Predictors of Susceptibility to Infidelity GARY W. LEWANDOWSKI JR. ROBERT A. ACKERMAN Department of Psychology Monmouth University West Long Branch, NJ ABSTRACT. The present authors investigated whether an individual s motivations that are related to need fulfillment and self-expansion within a romantic relationship can predict self-reported susceptibility to infidelity. A sample of 109 college students (50 men, 59 women) who were in dating relationships completed questionnaires that assessed 5 types of variables of need fulfillment (i.e., intimacy, companionship, sex, security, and emotional involvement), 3 types of self-expansion variables (i.e., self-expansion, inclusion of the other in the self, and potential for self-expansion), and susceptibility to infidelity. As the present authors predicted, both sets of predictors (need fulfillment and self-expansion) significantly contributed to the variance in susceptibility to infidelity. The present findings indicated the possibility that, when a relationship is not able to fulfill needs or provide ample self-expansion for an individual, his or her susceptibility to infidelity increases. Key words: couple relationships, gender differences, infidelity, relationship quality, selfconcept INFIDELITY IS A SERIOUS RELATIONSHIP TRANSGRESSION that is widely condemned (Widmer, Treas, & Newcomb, 1998). In fact, infidelity is the most common reason that spouses give for divorce in a variety of cultures (Amato & Rogers, 1997). The recognition that one s partner has engaged in an extradyadic relationship (a romantic relationship with a person outside of the couple) often results in substantial distress (Buunk, 1995) and even physical violence (Daly & Wilson, 1988). Because of these negative consequences, an individual s perception of his or her susceptibility to infidelity and of his or her inten- The authors thank the following individuals for their help on the project: Nicole Bizzoco, Katherine Evans, Jennifer Krops, Christina Messina, Paulian Olech, and Krystle Serago. Address correspondence to Gary W. Lewandowski Jr., Department of Psychology, Monmouth University, West Long Branch, NJ 07764; glewando@monmouth.edu ( .) 389

2 390 The Journal of Social Psychology tions to engage in extradyadic behaviors has implications for the relationship that are potentially serious. For this reason, it is important for researchers to identify factors that relate to these feelings (Buss & Shackelford, 1997). In the present study, we focused on two sources of motivation in relationships fulfillment of relationship needs and self-expansion to determine whether they predict selfreported susceptibility to infidelity. A fundamental assumption for most romantic relationships is that of exclusivity, the belief that both individuals are emotionally and sexually committed to each other solely (Treas & Giesen, 2000). Despite this assumption, infidelity is fairly common. Although estimates vary, in a study of college dating relationships, Wiederman and Hurd (1999) found that 68% of women and 75% of men had been involved in some form of extradyadic activity. To help people understand the prevalence of extradyadic behavior in dating relationships, researchers have sought to identify correlates of the experience. Researchers have associated factors such as low sexual frequency (Thompson, 1983), the opportunity to engage in extradyadic behavior (Blumstein & Schwartz, 1983), and an individual s level of sociosexuality (i.e., an individual s willingness to engage in sexual relationships without commitment; Seal, Agostinelli, & Hannett, 1994) with a greater likelihood of engaging in extradyadic behavior. Perhaps the most widely studied correlates of infidelity have been gender and relationship satisfaction. Regarding gender, researchers have consistently found men to engage in more extradyadic relationships than do women (e.g., Seal et al., 1994; Wiederman, 1997; Wiederman & Hurd, 1999). However, recent researchers have suggested that the gap between men and women in the frequency of infidelity is narrowing (Atkins, Baucom, & Jacobson, 2001). In terms of satisfaction, generally those who report lower levels of satisfaction with the relationship are more likely to engage in extradyadic behaviors (Treas & Geisen, 2000), with this relationship being somewhat stronger in women (Glass & Wright, 1985). In one notable study, Drigotas, Safstrom, and Gentilia (1999) examined motivations for infidelity among college students in the context of the investment model. This model focuses on the effects of relationship satisfaction, quality of alternative partners, and investments (things put into the relationship that can not be easily retrieved) on commitment to the relationship. Using a prospective design, researchers found relationship factors such as low satisfaction, high quality of alternative partners, low investments, and low commitment to predict greater extradyadic involvement over the course of a semester and over Spring Break. Those findings indicated the possibility that qualities that are associated with the relationship may be able to predict extradyadic behavior. Susceptibility to Infidelity A slightly different approach to infidelity involves participants perceptions of their own susceptibility to infidelity. Banfield and McCabe (2001) asked 112

3 Lewandowski & Ackerman 391 women about their intentions of engaging in a series of extradyadic behaviors, such as kissing, dating, and sexual intercourse, over the next 6 months. Those researchers results indicated that infidelity intentions were negatively correlated with commitment and positively correlated with relationship satisfaction, past extradyadic behavior, and social support. The finding regarding satisfaction contradicts previous work (e.g., Drigotas et al., 1999) but may be the result of a purely female sample or the inaccuracy of participants predictions regarding their behavior. In a similar study of 107 newlywed couples, Buss and Shackelford (1997) examined susceptibility to infidelity in the context of personality factors. In that study, members of the couple individually provided percentage ratings of how likely they were to engage in each of six extradyadic behaviors ranging from flirting to having a serious affair. Although the estimated likelihood for engaging in extradyadic activities was generally low (perhaps because the participants were newlyweds), relatively high susceptibility to infidelity was correlated with high narcissism, low conscientiousness, and high psychoticism. Relatively high susceptibility to infidelity was also associated with each of low sexual satisfaction and low relationship satisfaction. Taken together, findings from the previous studies show that relationship factors and personality factors play roles in perceptions of susceptibility to infidelity. Need Fulfillment Past researchers have given ample attention to an individual s motivations for engaging in extradyadic behaviors that relate to personality and relationship factors. However, researchers have given limited attention to motivational constructs within relationships that may influence susceptibility to infidelity. For example, Drigotas and Rusbult (1992) believed that relationships help people pursue four goals or needs in addition to sexual ones. These additional needs include those of intimacy, companionship, security, and emotional involvement. Intimacy needs involve self-disclosure and confiding in the partner regarding secrets and personal feelings. Companionship needs involve joint activities with the partner such as spending time together and having fun together that result in a greater sense of closeness. Security needs involve depending on the relationship to add predictability and contentment. Emotional involvement needs involve one s sense of emotional connection with the partner in which the partner s experiences feel as one s own. Because these five needs are commonly fulfilled as parts of a romantic relationship, it seems likely that a relative lack of fulfillment in any of these areas could lead to problems in the relationship such as a greater perceived susceptibility to infidelity. That is, if the primary relationship is unable to fulfill a certain need of an individual, he or she may be somewhat motivated to seek fulfillment of that need through an extradyadic relationship.

4 392 The Journal of Social Psychology Self-Expansion Model Self-expansion is another motivation that operates in the context of romantic relationships. Specifically, Aron and Aron (1996) and Aron, Norman, and Aron (1998) have based the Self-Expansion Model on the notion that people are fundamentally motivated toward the goal of enhancing the self through close relationships. Individuals achieve self-expansion by acquiring new resources, perspectives, skills, abilities, insights, and the like that result in increased self-efficacy and an enhanced sense of self. One way in which an individual achieves self-expansion is by sharing activities and experiences with the current partner (Aron, Norman, Aron, & Lewandowski, 2003). An individual s engagement in activities that are self-expanding (i.e., novel and challenging) is negatively correlated with his or her boredom and positively correlated with relationship quality and excitement. The Self-Expansion Model further indicates that self-expansion is facilitated by inclusion of the other in the self (Aron, Aron, Tudor, & Nelson, 1991). This process involves viewing one s relationship partner as part of the self so that the distinction between self and other blurs. That is, a blending of self and other in regards to resources, characteristics, and skills results in self-expansion. Both (a) inclusion of the other in the self specifically and (b) self-expansion generally are positively correlated with relationship satisfaction (Aron & Aron, 1996). As a result, if a relationship provides insufficient self-expansion, an individual in that relationship may be motivated to meet their expansion needs through other sources such as an extradyadic relationship. Similarly, if a person feels he or she cannot include the partner in the self, a greater susceptibility to infidelity may result. Previous researchers of self-expansion and inclusion of the other in the self have focused on individuals current experiences of each construct within the relationship. However, it seems likely that if self-expansion is a fundamental motivation within relationships, then individuals perceptions of a relationship s ability to provide self-expansion in the future would be especially important. These perceptions would seem particularly relevant to decisions concerning faithfulness within the relationship. That is, if a person believes that the current relationship has the potential to provide self-expansion in the future, there is little reason to leave the relationship or seek alternatives. Conversely, if the relationship appears to have little ability to provide self-expansion in the future, an individual may likely be motivated to seek self-expansion through an extradyadic relationship. Researchers predictions that have been based on need fulfillment and selfexpansion have been consistent with the Deficit Model of Infidelity (Thompson, 1983). The deficit model indicates that when the primary relationship is lacking in some areas (e.g., low satisfaction, not meeting sexual needs), infidelity results. The present study builds on this model by indicating two additional areas in which relationship deficiencies may lead to a greater perceived susceptibility to infidelity: need fulfillment and self-expansion. Additionally, researchers think that extradyadic relationships have the potential to provide achievements such as per-

5 Lewandowski & Ackerman 393 sonal growth and self-discovery that the primary relationship fails to offer (Buunk & Dijkstra, 2000). Unfortunately, researchers have not tested that idea empirically. However, the present application of the Self-Expansion Model to individuals self-perceptions of susceptibility to infidelity forms an important first step in research on this possible link between infidelity and the achievement of growth or expansion that the primary relationship lacks. Summary and Hypotheses To predict extradyadic behavior, past researchers have focused on relationship variables that are related to the Investment Model and on personality factors. In the present research, we sought to extend that research by examining motivations within the relationship need fulfillment and self-expansion that may relate to susceptibility to infidelity. To our knowledge, the present study represents the first empirical application of either concept to relationship infidelity. In the present effort, we tested the following hypotheses: Hypothesis 1: An intimate relationship s fulfillment of intimacy, companionship, sex, security, and emotional-involvement needs of an individual will be negatively correlated with his or her susceptibility to infidelity. Further, these associations will remain despite variations in other factors such as relationship length and gender. Hypothesis 2: In an intimate relationship, an individual s self-expansion, inclusion of the other in the self, and potential for self-expansion will be negatively correlated with the individual s susceptibility to infidelity. Further, these associations will remain despite variations in other factors such as relationship length and gender. The final purpose of the present study was to enhance researchers prediction of the likelihood of engagement in extradyadic relationships by accounting for several sets of variables (gender, relationship length, need fulfillment, self-expansion). On the basis of previous research, in the present research we hypothesized the following: Hypothesis 3: Each of these sets of variables gender, relationship length, need fulfillment, self-expansion will add a significant increment to the overall variance in susceptibility to infidelity. Participants Method Participants were 109 students (50 men, 59 women), from a private university in the northeast United States. We invited participants to participate in a study of relationship behaviors among people currently involved in a dating relationship. 1 Participants ages ranged from 18 years to 25 years (M age = 19.5 years, SD age = 1.45 years). Of all participants, a majority, or 84.4%, were Caucasian, 4.6%

6 394 The Journal of Social Psychology were Asian American, 4.6% were African American, 4.6% were Hispanic American, 0.9% were other, and 0.9% did not respond. Of all participants, a majority, or 53.2%, were freshmen, 19.3% were sophomores, 18.3% were juniors, and 9.2% were seniors. The average relationship length was 75 weeks, or approximately 1 year and 6 months (range = weeks; 8 participants did not respond). A majority of participants or 85.3% were dating exclusively, whereas 14.7% were dating casually. We recruited participants through the university s participant pool, and participants earned course credit for their participation. Measures Each member of groups of 1 6 participants completed a questionnaire packet that asked about his or her current relationship and a few demographic traits. Need-fulfillment measure. A need-fulfillment measure asked participants to Think about the needs you have within your current romantic relationship. Please use the space to the left of each need to indicate the extent to which each need was actually fulfilled by your partner, using the following rating scale (Le & Agnew, 2001). The measure consisted of five items, one for each of the five relationship needs (intimacy, companionship, sex, security, and emotional involvement). Each need preceded a brief explanation. For example, the security need was described as follows: These needs are related to having a relationship you can count on, one that makes your life more stable and comfortable. Participants responded using a 7-point Likert-type scale ranging from 0 (not fulfilled by my partner) to 3 (somewhat fulfilled by my partner) and to 6 (completely fulfilled by my partner). Self-expansion questionnaire. A self-expansion questionnaire assessed the extent to which a relationship was experienced as expanding the self through increased novelty and challenge (Lewandowski & Aron, 2002; SEQ). Example items include, How much does your partner help to expand your sense of the kind of person you are? ; How much has knowing your partner made you a better person? ; and How much do you see your partner as a way to expand your own capabilities? Participants responded on a 7-point Likert-type scale ranging from 1 (not very much) to 7 (very much). In two studies, Lewandowski and Aron have found this 14-item measure to be unifactorial with Cronbach s alphas of.87 and.89. In the present study, the measure s alpha was.86. Inclusion of the other in the self. A measure of inclusion of the other in the self was a single item that consisted of seven pairs of overlapping circles labeled to represent the self and the partner. Pairs of circles ranged from two circles with no overlap to a pair of circles that almost completely overlap (Aron, Aron, & Smollan, 1992). In a sample of romantic relationships, Aron et al. (1992) report-

7 Lewandowski & Ackerman 395 ed alternate-form reliability of.95 and test reliability over 2 weeks of.85. The scale has demonstrated strong predictive and construct validity as a general measure of closeness, and researchers have widely used it in relationship research. Potential for self-expansion. A measure of potential for self-expansion that we designed for the purpose of the present study focused on how much potential the current relationship had for self-expansion in the future. Example items included, I feel that my current relationship will give me opportunities to grow in the future and I feel that my relationship cannot offer me anything new in the future. The measure consisted of five items and used a 7-point Likert-type scale ranging from 1 (strongly disagree) to 7 (strongly agree). In the present study, the measure s alpha was.81. Infidelity intentions. A measure of infidelity intentions assessed participants intentions to commit emotional or sexual infidelity (Banfield & McCabe, 2001). The measure asked participants, Within the next 6 months which of the following do you intend to engage in with someone other than your regular partner? Participants responded on a 7-point Likert-type scale ranging from 1 (strongly disagree) to 7 (strongly agree) for six behaviors: casual friendship, deep love relationship, kissing, hugging and caressing, sexual intimacy without intercourse, sexual intercourse. Although Banfield and McCabe (2001) originally designed the subscales to distinguish emotional infidelity from sexual infidelity, in the present study we combined the subscales into one scale as did Banfield and McCabe ultimately. In the present study, the measure s alpha was.89. Susceptibility to infidelity. A measure of susceptibility to infidelity, developed by Buss & Shackelford (1997), asked participants how likely they were to engage in six forms of infidelity: flirt, passionately kiss, go on a romantic date, have a one night stand, have a brief affair, have a serious affair. Participants responded on an 11-point Likert-type scale ranging from 0% to 100% by 10% intervals. In the present study, the measure s alpha was.89. Results Table 1 shows means and standard deviations for key variables in the present study. Table 2 shows correlations. The two measures of susceptibility to infidelity were highly correlated, r =.69, p <.001. Consequently, we combined them for all subsequent analyses. 2 We created the combined score by averaging the z score from each scale. Need-Fulfillment Variables (Hypothesis 1) To test Hypothesis 1, we ran several correlational analyses, which Table 2 shows. As we hypothesized, each of the five types of relationship needs (i.e.,

8 396 The Journal of Social Psychology TABLE 1. Descriptive Statistics for Study s Variables Regarding Need Fulfillment, Self-Expansion, and Susceptibility to Infidelity Variables M SD Need fulfillment Intimacy needs Companionship needs Sexual needs Security needs Emotional-involvement needs Self-expansion Self-expansion Inclusion of other in the self Potential for self-expansion Susceptibility to infidelity Infidelity intentions Percent likelihood of infidelity Note. n = 109. intimacy, r =.27, p =.004; companionship, r =.30, p =.001; sex, r =.25, p =.01; security, r =.40, p <.001; and emotional involvement, r =.26, p =.006) were negatively correlated with susceptibility to infidelity. These results indicated that when relationship needs were not fulfilled, participants reported being more susceptible to committing relationship infidelity. To test the second part of Hypothesis 1, we ran several multiple regression analyses by entering simultaneously with relationship length and gender each variable that was related to need fulfillment. In each case, the association between each relationship need and susceptibility to infidelity remained significant. Additionally, in each case the partial r in the regression equation (measuring the unique association of each relationship need) was similar to the zero-order correlation (.29,.28,.24,.36, and.27, respectively). Self-Expansion Variables (Hypothesis 2) To test Hypothesis 2, we ran several correlational analyses, which Table 2 shows. As we hypothesized, self-expansion, r =.36, p <.001; inclusion of the other in the self, r =.44, p <.001; and potential for self-expansion, r =.50, p

9 Lewandowski & Ackerman 397 TABLE 2. Correlations Among Key Variables Variable Susceptibility to infidelity (z score).27***.30***.25**.40****.26***.36****.44****.50**** 2. Intimacy needs.48****.24**.48****.39****.41****.21**.37**** 3. Companionship needs.27***.44****.36****.47****.36****.43**** 4. Sexual needs *** Security needs.53****.48****.37****.43**** 6. Emotional-involvement needs.49****.22**.50**** 7. Self-expansion.40****.68**** 8. Inclusion of other in the self.29*** 9. Potential for self-expansion Note. For Variables 1 7 and 9, n = 109. For Variable 8, n = 101. Higher score indicates greater magnitude. All analyses were two-tailed. **p <.05. ***p <.01. ****p <.001.

10 398 The Journal of Social Psychology <.001; were all negatively correlated with susceptibility to infidelity. These results indicated that when participants experienced low self-expansion, inclusion of the other in the self, or potential for self-expansion, susceptibility to relationship infidelity increased. To test the second part of Hypothesis 2, we ran several multiple regression analyses by entering simultaneously with relationship length and gender each variable that was related to self-expansion. In each case, the association between the particular self-expansion variable and susceptibility to infidelity remained significant. Additionally, in each case the partial r in the regression equation (measuring the unique association of each relationship need) was similar to the zeroorder correlation (.33,.42, and.49, respectively). Prediction of Susceptibility to Infidelity We conducted a hierarchical regression analysis by sets for susceptibility to infidelity. The first set consisted of demographic variables: gender and relationship length. The second set consisted of need-fulfillment variables: intimacy, companionship, sex, security, and emotional involvement. And the third set consisted of self-expansion variables: self-expansion, inclusion of the other in the self, and potential for self-expansion. Table 3 shows the results of the analysis. As Table 3 shows, the contribution of the first set (demographics) to predicting the dependent variable was significant, R 2 =.12, p =.002. The contribution of TABLE 3. Hierarchical Multiple Regression by Sets Predicting Susceptibility to Infidelity From Demographics, Need Fulfillment, and Self-Expansion Variable β R 2 F Overall R 2 Step 1 Gender.29*** Relationship length.13.12*** 6.55***.12 Step 2 Intimacy needs.10 Companionship needs.06 Sexual needs.11 Security needs.23* Emotional-involvement needs.06.15*** 3.72***.27 Step 3 Self-expansion.11 Inclusion of other in the self.27*** Potential for self-expansion.45****.17**** 9.30***.44 Note. N = 101. Gender was dummy coded (Male = 1, Female = 2). *p <.10. **p <.05. ***p <.01. ****p <.001.

11 Lewandowski & Ackerman 399 the second set (need fulfillment) significantly increased the account of the variance, R 2 =.15, p =.004. The contribution of the third set (self-expansion) also significantly increased the account of the variance, R 2 =.17, p <.001. Thus, as we hypothesized, each set of variables significantly contributed to predicting susceptibility to infidelity. Overall, the variables in this analysis accounted for 44% of the variance in susceptibility to infidelity. Because gender has traditionally been seen as a primary determinant of infidelity, we ran an additional analysis without gender and relationship length in Step 1. In this analysis, the set of need-fulfillment variables significantly increased the account of the variance, R 2 =.21, p <.001. Adding the set of selfexpansion variables also significantly increased the account of the variance, R 2 =.19, p <.001. Thus, each set of variables significantly contributed to predicting susceptibility to infidelity. Overall, the variables in this analysis accounted for 40% of the variance in susceptibility to infidelity. Exploratory Analyses Although we did not hypothesize regarding gender, and it was not the focus of the present study, past researchers have suggested that gender plays a key role in susceptibility to infidelity. To test this possibility, in the present study we computed a t test with gender as the independent variable and susceptibility to infidelity as the dependent variable. Results indicated a significant difference, t(101) = 3.40, p =.001 (two-tailed), effect size d =.68, in which men (M = 0.39) are more susceptible to infidelity than are women (M = 0.20). 3 We ran a series of analyses to determine whether there were gender differences on any of the need-fulfillment or self-expansion variables. Results from those analyses indicated significant differences for self-expansion, t(101) = 2.01, p =.05 (two-tailed), effect size d =.40; and need for security, t(101) = 2.05, p =.04 (two-tailed), effect size d =.41. Differences indicated that women experienced more self-expansion and had a greater need for security than did men. Discussion The purpose of the present study was to determine the association between various relationship motivations and susceptibility to infidelity. The present findings supported the hypotheses and were consistent with previous research. As we hypothesized, each of the five types of need-fulfillment variables intimacy, companionship, sex, security, and emotional involvement was negatively correlated with susceptibility to infidelity. Also as we hypothesized, selfexpansion, inclusion of the other in the self, and potential for self-expansion were all negatively correlated with susceptibility to infidelity. In each case, the association between the various relationship motivations and susceptibility to infidelity remained after we controlled for gender and relationship length.

12 400 The Journal of Social Psychology Finally, all three sets of predictors (demographics, need fulfillment, and selfexpansion) significantly contributed to the account of the variance in susceptibility to infidelity. Need Fulfillment Past researchers have touched on the ability of relationships to satisfy needs primarily sexual needs (e.g., Seal et al., 1994) and its relation to infidelity. The present findings build up those findings by indicating the possibility that when a relationship is not fulfilling other needs (e.g., intimacy, companionship, security, and emotional involvement), individuals are more likely to engage in extradyadic relationships. One possible explanation for this possibility is that need fulfillment is associated with positive feelings that are then associated with the relationship itself. This explanation is consistent with previous work that links need fulfillment with positive emotions (Le & Agnew, 2001) and with well-being (Bohlander, 1999). Because of this association, it is possible that need fulfillment serves as a proxy for relationship satisfaction. In fact, one common measure of relationship satisfaction includes How well does your partner meet your needs? among its items (Hendrick, 1988). In light of the common link between relationship satisfaction and extradyadic behavior (e.g., Atkins et al., 2001; Drigotas et al., 1999; Glass & Wright, 1985; Prins, Buunk, & VanYperen, 1993; Treas & Giesen, 2000), the association between need fulfillment and susceptibility to infidelity is a fertile area for future research. Self-Expansion Model The present findings indicate the possibility that when relationships provide lower amounts of self-expansion, inclusion of the other in the self, and potential for future self-expansion, there is a greater susceptibility to infidelity. A basic principle of the Self-Expansion Model is that enhancing the self is a fundamental motive that is satisfied in relationships through inclusion of the other in the self (Aron & Aron, 1996). Further, Aron and Aron (1986) stated, When barriers are put between individuals and possible opportunities to expand, individuals tend to circumvent those barriers (p. 125). Therefore, as the present findings seem to indicate, if a person is unable to meet self-expansion goals in the context of the primary relationship, he or she can seek selfexpansion in a new extradyadic relationship, which would result in increased feelings of susceptibility to infidelity. Many prior researchers of infidelity have focused on the Investment Model (e.g., Drigotas et al., 1999), relationship satisfaction (e.g., Atkins et al., 2001), and gender (e.g., Wiederman, 1997). However, the present findings that were related to need fulfillment and self-expansion represent the first time researchers have used either construct to understand infidelity. The value in use of these con-

13 Lewandowski & Ackerman 401 structs in a novel context is evident from the finding that they account for 40% of the variance in susceptibility to infidelity. These results confirm the importance of considering need-fulfillment and self-expansion motivations when researchers try to understand extradyadic behavior. Gender One of the more robust findings in the infidelity literature is that men s proclivity toward extradyadic behavior is greater than that of women (e.g., Hansen, 1987; Seal et al., 1994; Wiederman & Hurd, 1999). The present findings support this general finding: Men reported feeling more susceptible to infidelity than did women. In addition, gender accounted for 12% of the variance in susceptibility to infidelity when gender was included in Step 1 of the hierarchical regression. However, it is important that the association between each of the need-fulfillment and self-expansion variables and susceptibility to infidelity was not significantly diminished when we controlled for gender. Taken together, these results indicate the possibility that although gender is significantly associated with susceptibility to infidelity, need fulfillment and self-expansion are other important constructs that can help researchers understand extradyadic behaviors. Limitations Like any other study, the present study suffers from limitations despite its strengths. It is important to note that susceptibility to infidelity does not equate with actual infidelity. As mentioned by Buss and Shackelford (1997), there are likely individuals within a sample who report a high likelihood of cheating on their partners but who will never actually engage in the behavior because of other factors (e.g., opportunity, changes in the relationship, etc.). It is also possible that participants underreport the likelihood of cheating because of social-desirability concerns (a common issue in infidelity research). Finally, the sample may not be fully representative of the general population and may only generalize to dating relationships. Future Directions and Applications Future researchers should try to determine how closely a person s intentions or perceived likelihood of infidelity match actual extradyadic behavior. One benefit of looking at susceptibility to infidelity is that it allows for the potential application of relationship interventions that focus on the prevention of infidelity. This might be more beneficial than dealing with the implications of actual infidelity on the relationship. Future researchers could examine whether participating in self-expanding activities (e.g., Aron et al., 2003) could resolve feelings of insufficient expansion, ultimately resulting in decreased susceptibility to infidelity.

14 402 The Journal of Social Psychology In conclusion, the present study contributes to researchers understanding of the issue of infidelity by examining two constructs need fulfillment and selfexpansion that have not been previously applied to the issue. The present findings indicate the possibility that when an intimate relationship is not able to fulfill the individuals needs and provide them with ample self-expansion, their susceptibility to infidelity increases. NOTES 1. Of all participants, 14 identified their relationship status as either engaged or married, and we omitted them from the analyses for failing to meet the inclusion criteria of the present study (i.e., currently in a dating relationship). 2. We also conducted analyses separately for infidelity intentions and infidelity likelihood. In all analyses, the pattern of results for each variable was the same. REFERENCES Amato, P. R., & Rogers, S. J. (1997). Longitudinal study of marital problems and subsequent divorce. Journal of Marriage and the Family, 59, Aron, A., & Aron, E. N. (1986). Love and the expansion of the self: Understanding attraction and satisfaction. New York: Hemisphere. Aron, A., & Aron, E. N. (1996). Self and self-expansion in relationships. In G. J. O. Fletcher & J. Fitness (Eds.), Knowledge structures in close relationships: Social psychological approach (pp ). Mahwah, NJ: Erlbaum. Aron, A., Aron, E. N., & Smollan, D. (1992). Inclusion of other in the self scale and the structure of interpersonal closeness. Journal of Personality and Social Psychology, 63, Aron, A., Aron, E. N., Tudor, M., & Nelson, G. (1991). Close relationships as including other in the self. Journal of Personality & Social Psychology, 60, Aron, A., Norman, C. C., & Aron, E. N. (1998). Self-expansion model and motivation. Representative Research in Social Psychology, 22, Aron, A., Norman, C. C., Aron, E. N., & Lewandowski, G. W., Jr. (2003). Shared participation in self-expanding activities: Positive effects on experienced marital quality. In P. Noller & J. Feeney (Eds.), Marital interaction (pp ). New York: Cambridge University Press. Atkins, D. C., Baucom, D. H., & Jacobson, N. S. (2001). Understanding infidelity: Correlates in a national random sample. Journal of Family Psychology, 15, Banfield, S., & McCabe, M. P. (2001). Extra relationship involvement among women: Are they different from men? Archives of Sexual Behavior, 30, Blumstein, P., & Schwartz, P. (1983). American couples: Money, work, sex. New York: William Morrow. Bohlander, R. W. (1999). Differentiation of self, need fulfillment and psychological wellbeing in married men. Psychological Reports, 84, Buss, D. M., & Shackelford, T. K. (1997). Susceptibility to infidelity in the first year of marriage. Journal of Research in Personality, 31, Buunk, B. P. (1995). Sex, self-esteem, dependency and extradyadic sexual experience as related to jealousy responses. Journal of Social and Personal Relationships, 12, Buunk, B. P., & Dijkstra, P. (2000). Extradyadic relationships and jealousy. In C. Hendrick & S. S. Hendrick (Eds.), Close relationships: Sourcebook (pp ). Thousand Oaks, CA: Sage.

15 Lewandowski & Ackerman 403 Daly, M., & Wilson, M. (1988). Evolutionary social psychology and family homicide. Science, 242, Drigotas, S. M., & Rusbult, C. E. (1992). Should I stay or should I go? A dependence model of breakups. Journal of Personality and Social Psychology, 62, Drigotas, S. M., Safstrom, C. A., & Gentilia, T. (1999). An investment model prediction of dating infidelity. Journal of Personality and Social Psychology, 77, Glass, S. P., & Wright, T. L. (1985). Sex differences in type of extramarital involvement and marital dissatisfaction. Sex Roles, 12, Hansen, G. L. (1987). Extradyadic relations during courtship. Journal of Sex Research, 23, Hendrick, S. S. (1988). Generic measure of relationship satisfaction. Journal of Marriage and the Family, 50, Le, B., & Agnew, C. (2001). Need fulfillment and emotional experience in interdependent romantic relationships. Journal of Social and Personal Relationships, 18, Lewandowski, G. W., Jr., & Aron, A. (2002, February). Self-expansion scale: Construction and validation. Paper presented at the third annual meeting of the Society of Personality and Social Psychology, Savannah, GA. Prins, K. S., Buunk, B. P., & VanYperen, N. W. (1993). Equity, normative disapproval and extramarital relationships. Journal of Social and Personal Relationships, 10, Seal, D. W., Agostinelli, G., & Hannett, C. A. (1994). Extradyadic romantic involvement: Moderating effects of sociosexuality and gender. Sex Roles, 3, Thompson, A. P. (1983). Extramarital sex: Review of the research literature. Journal of Sex Research, 19, Treas, J., & Giesen, D. (2000). Sexual infidelity among married and cohabiting Americans. Journal of Marriage and the Family, 62, Widmer, E. D., Treas, J., & Newcomb, R. (1998). Attitudes toward nonmarital sex in 24 countries. Journal of Sex Research, 35, Wiederman, M. W. (1997). Extramarital sex: Prevalence and correlates in a national survey. Journal of Sex Research, 34, Wiederman, M. W., & Hurd, C. (1999). Extradyadic involvement during dating. Journal of Social and Personal Relationships, 16, Received July 13, 2005 Accepted August 31, 2005

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