Evolution and Human Behavior xx (2012) xxx–xxx Review Article Sex differences in jealousy: a meta-analytic examination ⁎ Brad J. Sagarina, , Amy L. Martina, Savia A. Coutinhoa, John E. Edlundb, Lily Patela, John J. Skowronskia, Bettina Zengela aNorthern Illinois University, DeKalb, IL 60115, USA bRochester Institute of Technology, Rochester, NY 14623, USA Initial receipt 5 January 2012; final revision received 27 February 2012 Abstract The theory of evolved sex differences in jealousy predicts sex differences in responses to sexual infidelities and emotional infidelities. Critics have argued that such differences are absent in studies that use continuous measures to assess responses to hypothetical infidelities or in studies that assess responses to real infidelities. These criticisms were tested in two random-effects meta-analyses of 40 published and unpublished papers (providing 209 effect sizes from 47 independent samples) that measured sex differences in jealousy using continuous measures. A significant, theory-supportive sex difference emerged across 45 independent samples using continuous measures of responses to hypothetical infidelities, g*=0.258, 95% confidence interval (CI) [0.188, 0.328], pb.00001. Measured emotion significantly moderated effect size. Effects were strongest when measures assessed distress/upset (g*=0.337) and jealousy (g*=0.309). Other commonly measured negative emotions yielded weaker effects, including hurt (g*=0.161), anger (g*=0.074), and disgust (g*=0.012). Across the 45 independent samples, six significant moderators emerged: random sampling, population type (student vs. nonstudent samples), age, inclusion of a forced-choice question, number of points in the response scale, and year of publication. A significant, theory-supportive effect also emerged across seven studies assessing reactions to actual infidelities, g*=0.234, 95% CI [0.020, 0.448], p=.03. Results demonstrate that the sex difference in jealousy neither is an artifact of response format nor is limited to responses to hypothetical infidelities. © 2012 Elsevier Inc. All rights reserved. Keywords: Jealousy; Evolution; Sex differences; Meta-analysis 1. Introduction As evidenced by citation rates (336 for Buss et al. and 284 for Daly et al. according to the Web of Science as of this Men and women both react with jealousy in response to writing), the theory has been influential and has inspired a either a partner's sexual infidelity or his/her emotional number of additional predictions and studies (Buss & infidelity. However, according to the theory of evolved sex Haselton, 2005). However, the theory has also caused differences in jealousy (Buss, Larsen, Westen, & Semmel- substantial controversy. Indeed, many papers critical of the roth, 1992; Daly, Wilson, & Weghorst, 1982; Symons, theory have appeared in some of psychology's flagship 1979), the challenge of ensuring paternal investment exerted journals, including Psychological Science (e.g., DeSteno, selective pressures on women that boosted their jealousy 2010; Harris, 2002), Journal of Personality and Social response to emotional infidelity. In comparison, the theory Psychology (e.g., DeSteno, Bartlett, Braverman, & Salovey, suggests that the challenge of paternal uncertainty exerted 2002), Personality and Social Psychology Bulletin (e.g., selective pressures on men that boosted their jealousy Berman & Frazier, 2005), Personality and Social Psychol- response to sexual infidelity. Hence, the sexes are theorized ogy Review (e.g., Harris, 2003a), and Trends in Cognitive to differ in the patterns of jealousy exhibited in response to Sciences (e.g., Buller, 2005). emotional infidelities and sexual infidelities. One source of controversy lies in methodology. A primary methodology used to test the theory of evolved sex differences in jealousy is the forced-choice dilemma ⁎ Corresponding author. Department of Psychology, Northern Illinois University, DeKalb, IL 60115, USA. Tel.: +1 815 753 7067; fax: +1 815 753 pioneered by Buss et al. (1992). This methodology instructs 8088. women and men to think about a hypothetical situation in E-mail address: [email protected] (B.J. Sagarin). which their romantic partner has become interested in 1090-5138/$ – see front matter © 2012 Elsevier Inc. All rights reserved. doi:10.1016/j.evolhumbehav.2012.02.006 2 B.J. Sagarin et al. / Evolution and Human Behavior xx (2012) xxx–xxx someone else and to indicate which type of infidelity (sexual have failed to replicate the sex difference typically obtained or emotional) would cause greater distress. For example, with forced-choice measures. Similar nonreplications have Buss et al. presented participants with the following choice: been reported when participants reported their reactions to actual infidelity experiences (e.g., Harris, 2002). However, Please think of a serious committed romantic relationship that the data in these domains are mixed. For example, results of you have had in the past, that you currently have, or that you some studies using continuous measures do evince signif- would like to have. Imagine that you discover that the person icant sex differences (e.g., Edlund & Sagarin, 2009). with whom you've been seriously involved became interested Moreover, sex differences have emerged in some studies in someone else. What would distress or upset you more assessing responses to actual infidelity experiences (e.g., (please circle only one): Edlund, Heider, Scherer, Farc, & Sagarin, 2006). (A) Imagining your partner forming a deep emotional As noted by Edlund and Sagarin (2009, p. 76), both attachment to that person. proponents and opponents of the theory of evolved sex (B) Imagining your partner enjoying passionate sexual differences in jealousy have tended to overgeneralize the intercourse with that other person. (p. 252) results yielded by their own studies: Researchers on both sides of the debate regarding sex Consistent with predictions of the theory of evolved sex differences in jealousy have often pointed to single studies differences in jealousy, a significantly greater proportion of as providing sufficient support for their position. Opponents men (60%) than women (17%) indicated that the sexual of the theory have sometimes considered a single failure to infidelity would cause them greater distress. Subsequent replicate the sex difference as sufficient evidence to refute the research using this method has generally duplicated this effect, theory. Likewise proponents of the theory have often so much so that results from Harris' (2003a) meta-analysis considered a single significant sex difference as firmly demonstrated that the sex difference in jealousy when assessed establishing the theory. We suggest that both sides should via the forced-choice method is reliable and robust. be wary of placing too much weight on the results of a single However, evidence favoring the theory has proven study—a tendency Tversky and Kahneman (1971) labeled the elusive when jealousy is assessed using continuous measures belief in the law of small numbers. (e.g., when response scales separately assess jealousy When the debate was first enjoined, the small number of responses to sexual infidelity and emotional infidelity). studies that had been conducted made it difficult to Such elusiveness has led critics to suggest that the sex definitively assess the conclusions offered by both sides in difference in jealousy is an artifact of the forced-choice the debate. However, one consequence of the debate was that method. For example, DeSteno (2010) argues: people kept on doing research, and the number of empirical studies examining sex differences in jealousy is now When jealousy related to sexual and emotional infidelity is assessed using various non-forced-choice response formats, sufficient to statistically address the controversy. To this no sex differences emerge; men and women both report end, we conducted several meta-analyses that serve to greater jealousy in response to sexual infidelity (DeSteno et synthesize the corpus of studies that examined sex al., 2002; Harris, 2003a). Yet a sex difference in jealousy differences in jealousy using continuous measures. These readily emerges from these same people when they complete meta-analyses pursued three main objectives: (a) to deter- a forced-choice measure (DeSteno & Salovey, 1996; DeSteno mine whether there is or is not a sex difference in jealousy et al., 2002)…. when jealousy is assessed with continuous measures, (b) to determine whether the sex difference appears in response to A second perceived shortcoming stems from the hypo- actual infidelity experiences (and whether the effects thetical scenarios used in most studies examining responses observed in those studies differ from those obtained in the to infidelity. These studies essentially assess participants' hypothetical scenario studies), and (c) to identify moderators predictions about how they would feel, not their emotional that can help to explain the diversity present in past findings. responses to actual infidelity. Citing potential errors in Before describing the meta-analyses, one issue needs to affective forecasts, critics have cast doubt on the results of be addressed: the proper statistical interpretation of the such research. Indeed, as noted by DeSteno (2010), Gilbert, results from the studies that have employed continuous Wilson, and their colleagues have documented systematic measures. This is discussed in the section that follows. errors in people's predictions of how they will feel