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Social Comparison Orientation in Monozygotic and Dizygotic Twins

Published online by Cambridge University Press:  10 November 2017

Pascal Huguet*
Affiliation:
University Clermont Auvergne and CNRS, LAPSCO, Clermont-Ferrand, France
Michèle Carlier
Affiliation:
Aix Marseille University, CNRS, LPC, Cognitive Psychology, Marseille, France
Conor V. Dolan
Affiliation:
Vrije Universiteit, Netherlands Twin Register & Department of Biological Psychology, Amsterdam, the Netherlands
Eco J. de Geus
Affiliation:
Vrije Universiteit, Netherlands Twin Register & Department of Biological Psychology, Amsterdam, the Netherlands
Dorret I. Boomsma
Affiliation:
Vrije Universiteit, Netherlands Twin Register & Department of Biological Psychology, Amsterdam, the Netherlands
*
address for correspondence: Pascal Huguet, University Clermont Auvergne and CNRS, LAPSCO, F-63000 Clermont-Ferrand, France. E-mail: pascal.huguet@uca.fr.

Abstract

Twin research has offered evidence that monozygotic (MZ) twins are more socially close than dizygotic (DZ) twins, but has not paid much attention to the way twins compare themselves with their co-twin. The few studies in this area suggest that ‘horizontal comparisons’ (social comparison motivated by solidarity or communion with others) matter more for MZ twins than for DZ twins, at least when the co-twin is the social comparison standard. Consistent with this view, we predicted higher interest in MZ twins relative to DZ twins to select their co-twin rather than other people in general as the social comparison standard. The Social Comparison Orientation (SCO) scale, which measures the inclination to compare with others in a horizontal rather than vertical mode (comparing either upward or downward), was administered in 90 MZ pairs and 57 same-sex DZ pairs (63% female; average age 18.06 years) from the Netherlands Twin Register. MZ twin pairs showed significantly higher SCO scores than DZ twin pairs (with a large effect size) on the co-twin SCO, whereas the two groups did not differ from each other on the general SCO excluding the co-twin as social comparison standard. In MZ twin pairs, anxiety was associated with social comparison with others in general, not with their co-twin. For both scales, twin resemblance was explained by additive genetic variance. The present findings provide direct evidence that horizontal comparisons with the co-twin are of particular importance for MZ twins.

Type
Articles
Copyright
Copyright © The Author(s) 2017 

It has long been known that twins may share a special kind of social relationship compared to non-twin siblings. Monozygotic (MZ) twins have on average closer relationships than dizygotic (DZ) twins, who themselves have closer relationships than non-twin siblings (Fortuna et al., Reference Fortuna, Goldner and Knafo2010; Fraley & Tancredy, Reference Fraley and Tancredy2012; Loehlin & Nichols, Reference Loehlin and Nichols1976; Mowrer, Reference Mowrer1954; Neyer, Reference Neyer2002; Penninkilampi-Kerola, Reference Penninkilampi-Kerola2005; Segal, Reference Segal1984; Segal et al., Reference Segal, Graham and Ettinger2013; Tancredy & Fraley, Reference Tancredy and Fraley2006; Thorpe, Reference Thorpe2003; Zazzo, Reference Zazzo1960, Reference Zazzo1976). Compared with DZ twins and non-twins, MZ twins also show greater cooperation (Segal, Reference Segal1984) and more tacit coordination with their co-twin during childhood, adolescence, and in older age (McGuire & Segal, Reference McGuire and Segal2013; Segal et al., Reference Segal, McGuire, Miller and Havlena2008, Reference Segal, Graham and Ettinger2013, Reference Segal, Munson, Marelich, Goetz and McGuire2014). This higher interdependency between MZ twins relative to DZ twins can also be found in pairs separated in infancy and reunited later (Segal et al., Reference Segal, Hershberger and Arad2003).

Because MZ twins share nearly all their genes while DZ twins share on average 50% of their segregating genes, people expect MZ twins to be more similar than DZ twins for any trait that is influenced by genes. The label ‘identical’ when talking about MZ is a good illustration of this expectation that leads parents, other family members, teachers, and friends to compare the twins on various characteristics, such as height, weight, skills and abilities, and social behavior (Ebeling et al., Reference Ebeling, Porkka, Penninkilampi-Kerola, Berg, Järvi and Moilanen2003; Stewart, Reference Stewart2000). Although these pressures towards uniformity may encourage and even force the twins to compare with their co-twin, this comparison did not receive much attention in twin research. This is relatively surprising as the non-volitional nature of ‘twinship’ also means that this comparison is often unavoidable (Noller et al., Reference Noller, Conway, Blakeley-Smith, Forgas and Fitness2008).

Social Comparison among Twins

Noller and colleagues (Noller, Reference Noller2005; Noller & Blakely-Smith, Reference Noller and Blakely-Smith2007; Noller et al., Reference Noller, Conway, Blakeley-Smith, Forgas and Fitness2008) collected retrospective self-reports of situations of asymmetrical (upward or downward) social comparisons and competition with their emotional component among same-sex sibling pairs (twins, adolescent and young adult siblings), which also allowed these authors to test Tesser's Self-Evaluation Maintenance (S-EM) model (Tesser, Reference Tesser and Berkowitz1988; Tesser & Schartz, Reference Tesser and Schwarz2001). According to this model, when one is outperformed by a close other on a task high in relevance to the self, a potentially self-threatening social comparison is created. When another outperforms on a task low in relevance to the self, the closer the other the greater the ‘self-reflected glory’, a reflection (rather than comparison) process where individuals benefit from their close others’ successful performance. As reported by Noller and colleagues (Noller, Reference Noller2005; Noller et al., Reference Noller, Conway, Blakeley-Smith, Forgas and Fitness2008), DZ twins and non-twins’ reports were generally consistent with the S-EM model whereas MZ twins’ reports were not. MZ twins tended on average to react positively to upward comparisons with their co-twin on self-relevant dimensions, suggesting that the very close relationship with their co-twin ‘buffered them against any problems related to competition and comparison’ (Noller et al., Reference Noller, Conway, Blakeley-Smith, Forgas and Fitness2008, p. 249; see also Veldkamp et al., Reference Veldkamp, van Bergen, de Zeeuw, Van Beijsterveldt, Boomsma and Bartels2017).

Complementary with Noller and colleagues’ approach, Watzlawik (Reference Watzlawik2009) examined what adolescent siblings actually perceive when they compare themselves with their counterparts, and found that MZ co-twins perceived fewer differences between them than did DZ co-twins and non-twin siblings. Although MZ twins did not perceive more similarities, they were the only group where the self-reported similarities outweighed the differences. As noted by Watzlawik (Reference Watzlawik2009), MZ twins may ‘have more difficulties in finding their individual niches — which does not necessarily have to be a disadvantage since the twin relationship offers a special support as well’ (p. 574).

The Present Research

Although the tendency to engage in social comparison is thought to be a universal human characteristic (Gilbert et al., Reference Gilbert, Price and Allan1995) — a ‘phylogenetically very old’ and ‘biologically very powerful’ tendency (to take Gilbert et al.’s own words) — there is evidence that the strength of this tendency varies between individuals (Gibbons & Buunk, Reference Gibbons and Buunk1999). In line with this idea, Gibbons and Buunk (Reference Gibbons and Buunk1999) developed the Iowa-Netherlands Comparison Orientation scale (hereafter referred to as SCO scale), measuring the inclination or willingness to compare one's accomplishment, situations, or experiences with those of others. The social comparison orientation (SCO) scale includes 11 items, such as ‘I always like to know what others in a similar situation would do’, and ‘I often compare myself with others with respect to what I have accomplished in life’. Based on a representative sample of Dutch citizens in all age groups, it revealed that there are as many high comparers as there are low comparers. Inter-items reliability (Cronbach's alpha) was very consistent across a variety of samples, ranging from 0.78 – 0.85 in the United States and the Netherlands. Likewise, test–retest correlations ranged from 0.71 for 3–4 weeks to 0.60 for a year in the United States (and Spain) and to 0.72 for 7.5 months in the Netherlands. The SCO scale was then adapted and successfully used in many countries; for example, Hungary, Poland, Turkey (Luszczynska et al., Reference Luszczynska, Gibbons, Piko and Tekozel2004), Spain (Buunk et al., Reference Buunk, Zurriaga, Peíró, Nauta and Gosalvez2005), and France (Jonas & Huguet, Reference Jonas and Huguet2008), to name but a few.

Of particular interest here, Buunk and Gibbons (Reference Buunk, Gibbons and Guimond2006) found that the SCO scale is associated with an interpersonal orientation, a construct that includes a strong empathy for others, a general sensitivity to the needs, moods, and criticisms of others, and an interest to mutual self-disclosure all aspects that are typical of individuals with a high interdependent self (Markus & Kitayama, Reference Markus and Kitayama1991; Swap & Rubin, Reference Swap and Rubin1983). As would be expected from the individuals with an interdependent self, Buunk and Gibbons (Reference Buunk, Gibbons and Guimond2006) also found that the SCO scale correlates positively with the communal orientation scale (Clark et al., Reference Clark, Ouellette, Powell and Milberg1987) measuring the inclination to care and help others. This pattern of correlations (the higher SCO scores, the higher interdependence, and communal values) may seem counter-intuitive, as also pointed out by Buunk and Gibbons (Reference Buunk, Gibbons and Guimond2006), since social comparison has traditionally been associated with a motivation toward differentiating oneself in a competitive way from others.

However, there is today ample evidence that two broad, independent dimensions underlie social comparison processes: a ‘vertical’ (better/worse than others) dimension of status, dominance, or agency (see Buunk et al., Reference Buunk, Collins, Taylor, Van Yperen and Dakof1990; Mussweiler, Reference Mussweiler2003; Suls et al., Reference Suls, Martin and Wheeler2002; Wills, Reference Wills1981; Wood, Reference Wood1989), and a ‘horizontal’ dimension of solidarity, friendliness, or communion (for a review, see Locke, Reference Locke, Krizan and Gibbons2014). In light of this useful distinction, it can reasonably be assumed that the SCO scale reflects the horizontal (more than vertical) dimension of social comparison. If MZ twins are more interdependent with their co-twin than are DZ twins, we reasoned, MZ twins should then score higher than DZ twins on a version of the SCO scale focusing specifically on the co-twin as social comparison standard. Likewise, MZ twins (but not necessarily DZ twins) should be higher on this co-twin version of the SCO scale than on its classic (general) version measuring the willingness to compare with people ‘in general’. Higher level of SCO towards the co-twin among MZ twins relative to DZ twins would clarify the meaning of social comparison among twins, and show its dependency on zygosity.

Materials and Methods

Participants

Participants were 147 young adult same-sex twin pairs (14.87–22.68 years of age, M = 18.06, SD = 1.53) recruited from the Netherlands Twin Registry (Boomsma et al., Reference Boomsma, Geus, Vink, Stubbe, Distel, Hottenga and Willemsen2006) as part of a larger study on the development of attention and cognition. The sample included 90 MZ pairs (30 MZ male pairs [MZ-M], 60 MZ female pairs [MZ-F]) and 57 same-sex dizygotic (SSDZ) twin pairs (23 SSDZ male pairs [SSDZ-M] and 34 SSDZ female pairs [SSDZ-F]). The four groups did not differ on age or non-verbal intelligence evaluated in a computerized form of the Raven advanced progressive matrices (Bartels et al., Reference Bartels, van Weegen, van Beijsterveldt, Carlier, Polderman, Hoekstra and Boomsma2012). None of the participants suffered from severe physical or mental handicaps. Prior to the study, participants and their parents (for participants under 18 years) signed an informed consent form. Zygosity was determined on the basis of DNA polymorphisms.

Measures

All data were collected at the Vrije Universiteit, Amsterdam. Participants from each pair were tested at the same time, independently in separate rooms. They performed a reasoning test (advanced Raven matrices) and then answered a short questionnaire including a measure of test-related anxiety (Spielberger et al., Reference Spielberger, Gorsuch, Lushene, Vagg and Jacobs1970; see appendix A) and the two versions of the SCO scale: the standard version assessing individual differences in SCO with others in general (thus excluding the co-twin), and a modified version where the words ‘others’ (or equivalent terms) were replaced by ‘my co-twin’ (hereafter referred to as general SCO and co-twin SCO, respectively, see appendix B). For both versions (11 items in each version), each participant indicated to what extent he/she agreed or disagreed with each item. Gibbons and Buunk (Reference Gibbons and Buunk1999) used a 5-point scale for the general SCO that ranged from 1 (strongly disagree) to 5 (strongly agree). In the present study, we used a 6-point scale (1 = strongly agree, 2 = agree, 3 = mostly agree, 4 = mostly disagree, 5 = disagree, and 6 = strongly disagree) to increase the discriminative power of the two versions of the SCO scale and avoid the use of a midpoint score (neither agree or disagree). The SCO scores therefore indicated higher SCO either with the co-twin (co-twin SCO) or with others in general excluding the co-twin (general SCO). Cronbach's alphas (taking the twin pair as unit of analysis) were high for the two versions of the SCO scale (αMZ = 0.88 and αDZ = 0.78 for the general SCO; 0.91 and 0.90, respectively, for the co-twin SCO). The two versions of the SCO scale were administered after the reasoning test for all participants so as not to explicitly prime social comparison-related cognitions during test performance.

Statistical Analysis

We carried out two analyses of variance (ANOVAs) with the mean of the twin pair as the unit of analysis. The first ANOVA was a 2 × 2 mixed design using zygosity (MZ vs. DZ) as an independent variable and type of SCO scale (Co-twin vs. General) as repeated measures. We performed a second mixed design ANOVA while adding twin pairs’ sex as independent variable. We note that the variance of the twin means is expected to vary as a function of zygosity, with the MZ variance being greater than the DZ variance. This implies a possible violation of homogeneity of error variances. To determine whether the results of the ANOVAs were affected by this violation, we repeated the analyses using the sandwich correction implemented in the SPSS generalized estimating equations (GEE) procedure (e.g., Dobson & Barnett, Reference Dobson and Barnett2008). Relations between SCO and anxiety were described with Person correlations. Twin correlations were calculated for MZ and DZ pairs, and genetic analyses were carried out in Mx (Neale et al., Reference Neale, Boker, Xie and Maes2006) for both versions of SCO to estimate the contribution of genetic and environmental factors to population variance in these scores.

Results

Social Comparison Orientation (SCO Scales)

In the first mixed design ANOVA all effects were significant: zygosity, F (1, 145) = 10.52, p = .0014, partial η2 = 0.07, SCO scale, F(1, 145) = 6.06, p = .015, partial η2 = 0.04, and zygosity by SCO scale interaction, F(1, 145) = 28.06, p < .0001, and partial η2 = 0.16. Using GEE we obtained the following test statistics: zygosity, χ2 (1) =12.09, p < .001; SCO scale, χ2(1) = 6.06, p = .015, and the interaction: χ2(1) = 27.28, p < .0001. The conclusions based on the ANOVA are therefore the same as those based on GEE.

Table 1 shows the four means and standard deviations. Consistent with our expectations, on the co-twin SCO scale, MZ twins showed higher scores than DZ twins, t(145) = 4.73, p < .0001, Cohen's d = 0.73, whereas both groups did not differ on the general SCO scale, t(145) = 0.26, p = .80, d = 0.05. Likewise, MZ twins showed higher scores on the co-twin SCO scale than on the general SCO scale, paired −t(89) = 2.37, p = .02, d = 0.35, whereas actually the reverse effect occurred in DZ twins, paired −t(56) = − 4.68, p < .0001, d = 0.88.

TABLE 1 Means and Standard Deviations for the Two Versions of the SCO Scale by Zygosity

The statistical analysis, which included twin pairs’ sex, revealed that female pairs scored higher than male pairs whatever the version of the SCO scale, F(1, 143) = 14.35, p < .0001, and η p 2 = 0.09 (on average on both scales, M = 44.6, SEM = 0.62 for females, and M = 40.78, SEM = 0.80, for males), with no significant zygosity × SCO × sex interaction, F(1, 143) = 1.48, p = .23, and η p 2 = 0.01). Using GEE we obtained the following test statistics: main sex effect: χ2 (1) = 15.74, p < .001; the 3-way interaction: χ2(1) = 1.57, p = .21. Once more, the ANOVA results and GEE results give rise to the same conclusions.

Although the first-born and the second-born co-twins have essentially the same age, they may define themselves as the younger or the elder (Noller et al., Reference Noller, Conway, Blakeley-Smith, Forgas and Fitness2008; Stewart, Reference Stewart2000; Yoon & Hur, Reference Yoon and Hur2006). We thus conducted a 2 × 2 mixed ANOVA design using zygosity (MZ vs. DZ) as an independent variable and type of SCO scale (Co-twin vs. General) as repeated measures separately for the younger twins and their elder counterparts. We found the same results as previously. In both age groups, MZ twins showed higher scores than DZ twins (ps ≤ .001) on the co-twin SCO scale, whereas MZ and DZ twins did not differ on the general SCO scale (ps ≥ .27). Likewise, in both age groups, MZ twins showed a higher score on the co-twin SCO scale than on the general SCO scale (especially the second-born; first-born, p = .10, d = 0.24; second-born, p = .01, d = 0.37), whereas the reversed effect was found in the first- and second-born DZ twins (ps ≤ .001, d = 0.67 and 0.78, respectively).

Self-Reports of Anxiety

As noted by Buunk and Gibbons (Reference Buunk, Gibbons and Guimond2006), responses on the general SCO scale also correlate with anxiety and neuroticism, although these correlations are lower than those with interpersonal and communal orientations. In line with this, the MZ twin pairs’ SCO scores correlated positively and significantly with their reports of anxiety for both versions of the scale, rs(88) = 0.39, p < .001 and 0.30, p = .004, for the general and co-twin versions of the SCO scale, respectively. However, the co-twin SCO-anxiety relationship was no longer significant, r (87) = 0.08, p = .45, when controlling for the general SCO, whereas the general SCO-anxiety relationship remained significant, r (87) = 0.28, p = .009, when controlling for the co-twin SCO. This indicates that MZ twins’ anxiety was associated with social comparison with others in general, but not with their co-twin. The SCO-anxiety relationships did not reach significance in DZ twins, rs (55) = 0.05 and 0.16, ps’ > .24, for the general and co-twin versions of the SCO, respectively.

Twin Correlations (ICC) and Genetic Analyses

MZ intraclass correlations were larger than DZ intraclass correlations for both scales. Co-twin version: 0.585 (95% CI [0.43, 0.71]) versus 0.271 (95% CI [0.013, 0.494]); general version: 0.616 (95% CI [0.469, 0.729]) versus 0.004 (95% CI [-0.255, 0.262]). For the co-twin version heritability was estimated at 59% and for the general version at 56%, with the remaining variance explained by non-shared environment.

Discussion

Twin research offers evidence that MZ twins are more socially interdependent than DZ twins, but has not paid much attention to the way twins compare themselves with their co-twins. The few studies in this area indicated that MZ twins, but not DZ twins, can benefit from their co-twin's success even when it occurs in self-relevant comparison dimensions (Noller et al., Reference Noller, Conway, Blakeley-Smith, Forgas and Fitness2008), suggesting that MZ twins’ close relationship with their co-twin actually protects them against any problems related to interpersonal competition. Consistent with decades of research on twins relationships, this finding and others (Watzlawik, Reference Watzlawik2009) seemed to indicate that MZ twins are more likely than DZ twins to experience social comparison with their co-twin in a horizontal mode motivated by solidarity or communion (see Locke, Reference Locke2003, Reference Locke, Krizan and Gibbons2014), as opposed to a vertical mode (comparing either upward or downward for a variety of reasons mostly related to status, dominance, or agency; see Buunk et al., Reference Buunk, Collins, Taylor, Van Yperen and Dakof1990; Mussweiler & Rüter, Reference Mussweiler and Rüter2003; Suls et al., Reference Suls, Martin and Wheeler2002; Wills, Reference Wills1981; Wood, Reference Wood1989, Reference Wood1996). The present findings strengthen this view.

In the SCO scale measuring mainly empathy for others — a special sensitivity to the needs, moods, and criticisms of others — and interest in mutual self-disclosure, we reasoned that MZ twins should display higher SCO scores than DZ twins when focusing specifically on their co-twin as a social comparison standard. This is exactly what we found. MZ twin pairs showed significantly higher SCO scores than DZ twin pairs (with a large effect size) on the co-twin SCO, whereas the two groups did not differ from each other on the general SCO excluding the co-twin as social comparison standard. This dissociation rules out any characterization of MZ twins as simply more interested than DZ twins by horizontal comparisons with people in general.Footnote 1 Consistent with this special interest of MZ twins in horizontal comparisons with their co-twin specifically, they also scored higher on the co-twin SCO relative to the general SCO, whereas the reverse effect was found in DZ twins. Furthermore, whereas higher interest in horizontal comparisons with the co-twin was unrelated to MZ and DZ twins’ self-reports of anxiety, this relationship proved significant and positive in MZ twins for comparisons excluding the co-twin (general SCO). Taken together, these findings can reasonably be taken as evidence that horizontal comparisons with the co-twin are of particular importance for MZ twins.

This conclusion does not mean that MZ twins never engage in vertical comparisons (upward or downward) with their co-twin (as also suggested by Watzlawik, Reference Watzlawik2009). The tendency to compare upward (i.e., with someone better off in a given domain), for example, is a powerful trend (Blanton et al., Reference Blanton, Buunk, Gibbons and Kuyper1999; Festinger, Reference Festinger1954; Huguet et al., Reference Huguet, Dumas, Monteil and Genestoux2001; Reference Huguet, Dumas, Marsh, Régner, Wheeler, Suls and Nezlek2009), which occurs early in cognitive development (Dumas et al., Reference Dumas, Huguet, Monteil and Ayme2005). As with many other individuals, MZ twins may deliberately engage in upward comparisons, at least with their co-twin, simply because these comparisons can reveal useful information about how to improve in such and such a domain (e.g., Buunk & Ybema, Reference Buunk, Ybema, Buunk and Gibbons1997; Taylor & Lobel, Reference Taylor and Lobel1989; Wood, Reference Wood1989). In non-twins or singletons, the reasons for choosing to compare upward and that might result in improved performance are numerous. As noted by Blanton et al. (Reference Blanton, Buunk, Gibbons and Kuyper1999), individuals may come to identify with successful targets (leading to imitation of the targets’ actions; Bandura, Reference Bandura1986), and/or set higher personal standards for evaluating their own success, which can motivate efforts toward these more challenging goals (e.g., Dumas et al., Reference Dumas, Huguet, Monteil and Ayme2005; Huguet et al., Reference Huguet, Galvaing, Monteil and Dumas1999, Reference Huguet, Galvaing, Dumas, Monteil, Forgas, Williams and Wheeler2000; Seta, Reference Seta1982). Observing others doing well can also endow individuals with a sense of their own potential (e.g., Buunk et al., Reference Buunk, Collins, Taylor, Van Yperen and Dakof1990; Lockwood & Kunda, Reference Lockwood and Kunda1997; Major et al., Reference Major, Testa, Bylsma, Suls and Wills1991), which may raise self-confidence and feelings of self-efficacy, with positive consequences on performance (see Multon et al., Reference Multon, Brown and Lent1991; Schunk, Reference Schunk1989). All these effects are likely in MZ twins due to the very close relationship with their co-twin conceived as a social comparison standard. As also noted by Locke (Reference Locke, Krizan and Gibbons2014), sharing a close relationship (Mussweiler & Rüter, Reference Mussweiler and Rüter2003; Pelham & Wachsmuth, Reference Pelham and Wachsmuth1995), potentially sharing the same fate (Lockwood & Kunda, Reference Lockwood and Kunda1997), sharing membership in a distinguishing and self-defining group (Brewer & Weber, Reference Brewer and Weber1994; Mussweiler & Bodenhausen, Reference Mussweiler and Bodenhausen2002), and sharing other rare or distinctive attributes (Brown et al., Reference Brown, Novick, Lord and Richards1992) have all been shown to enhance assimilation, especially upward assimilation (increased self-evaluation and/or performance following upward comparison), as opposed to upward contrast (decreased self-evaluation and/or performance following upward comparison; see also Huguet et al., Reference Huguet, Dumas, Marsh, Régner, Wheeler, Suls and Nezlek2009; Mussweiler, Reference Mussweiler2003; Wheeler & Suls, Reference Wheeler and Suls2007). Although the present findings indicate that horizontal comparisons with their co-twin is of particular importance in MZ twins, there are therefore good reasons to believe that MZ twins may also engage in vertical comparisons with beneficial effects on cognition, motivation, and emotion.

As suggested by Noller et al.’s (Reference Noller, Conway, Blakeley-Smith, Forgas and Fitness2008) findings, upward assimilation also seems to occur in MZ twins (but not in DZ twins) even when upward comparisons with the co-twin are forced by the social environment, a condition typically associated in non-twins or singletons with upward contrast and so negative effects on self-evaluation and performance (see Huguet et al., Reference Huguet, Dumas, Marsh, Régner, Wheeler, Suls and Nezlek2009; Marsh & Hau, Reference Marsh and Hau2003). Strongly motivated by horizontal comparisons emphasizing solidarity and communion with their co-twin, MZ twins, perhaps more than any other models of close relationships, are thus likely to benefit from upward comparisons with their co-twin even when these comparisons are forced rather than deliberate.

Future research, however, is needed to estimate the moderating role of horizontal comparisons operating within twin pairs on the influence of vertical comparisons, especially those arising under the pressure of the social environment. Likewise, future research might help specify the role — if any — of horizontal comparisons in phenomena, such as the tacit coordination that typically occur within twins pairs, or the self-confidence that twins may derive from their co-twin, to name but a few. For example, Locke (Reference Locke2005) showed in non-twins or singletons that perceiving similarities with a social comparison standard's desirable attributes, and dissimilarities with undesirable attributes, enhanced self-confidence. Ironically, assimilation being the default mindset within MZ twin pairs, MZ twins may perceive similarities with the co-twin's desirable as well as undesirable attributes, resulting in decreased self-confidence when the salience of undesirable attributes prevail for some reasons. Thus, although social comparison is a fundamental feature of social life in humans, perhaps especially in twins, much remains to be done to integrate it with our understanding of twins’ relationships.

Acknowledgments

We warmly thank all twins who took part in the study and Tinca Polderman, Aafke van Santen, and Felice van Weegen for data collection. This work was supported by ANR grant Twins-2010 (P. H., M.C.), Aix Marseille University (P. H., M.C.), CNRS (P.H., M.C.), Vrije University, Netherlands Twin Register & Department of Biological Psychology (C.D., E.G., D.B).

Conflict of Interest

None.

Ethical Standards

The authors assert that all procedures contributing to this work comply with the ethical standards of the relevant national and institutional committees on human experimentation and with the Helsinki Declaration of 1975, as revised in 2008. The study was approved by the Central Committee on Research Involving Human Subjects, and the institutional review board of the VU University Amsterdam.

Appendix A

Anxiety Scale

Each participant indicated to what extent he/she agreed or disagreed with each of the eight following items: «While taking the tests, you felt anxious», «comfortable», «jittery», «worried», «at ease», «nervous», «relaxed», and «calm». We used a 6-point scale that ranged from: (1) Strongly agree (2) Agree (3) Mostly agree (4) Mostly disagree (5) Disagree and (6) Strongly disagree. Items 2, 5, 7, and 8 were reverse coded. A higher score indicated higher anxiety. Cronbach's alphas (taking the twin pair as unit of analysis) were high and identical in both groups (αMZ and αDZ = 0.91).

Appendix B

Items and Factor Loadings for the Two Versions of the SCO Scale (General vs. Co-twin).

Footnotes

*

These authors contributed equally.

1 The fact that female pairs (both MZ and DZ) scored higher than male pairs whatever the version of the SCO scale (co-twin vs. general) strengthens the view that this scale measures an interpersonal orientation rather than competition. There is indeed ample evidence that male and female (culturally mandated) sense of self depends on separation and independence for men, and connection and interdependence for women (see Maccoby & Jacklin, Reference Maccoby and Jacklin1974; Markus & Kitayama, Reference Markus and Kitayama1991; Swap & Rubin, Reference Swap and Rubin1983), with strong implications early in the course of cognitive development (e.g., Huguet & Monteil, Reference Huguet and Monteil1995).

A principal-component analysis (PCA) on the general SCO scale (11 items) was conducted on the whole sample of twins. The raw data was the mean score of the pair for each item. Although before rotations all items loaded on the first factor (>0.40), two factors similar to those found by Gibbons and Buunk (Reference Gibbons and Buunk1999) were extracted with eigenvalue > 1. These factors explained 41.82% and 16% of the variance, respectively. After varimax (orthogonal) rotations, Factor 1, labeled ‘Ability’ by Gibbons and Buunk (Reference Gibbons and Buunk1999), comprised items #1 to #6 (5 of which concerned performance); Factor 2, labeled ‘Opinion’, comprised items #7 to #10.The PCA conducted on the co-twin version of the SCO scale showed the same factor structure. Statistical analyses on the two sub-scales (Ability and Opinion) showed a higher SCO score on the Opinion sub-scale relative to the Ability sub-scale whatever the version of the SCO scale (General vs. Co-twin), and provided no additional information on the differences between MZ and DZ, compared to those obtained on the full scales.

References

Bandura, A. (1986). The explanatory and predictive scope of self-efficacy theory. Journal of Social and Clinical Psychology, 4, 359373.CrossRefGoogle Scholar
Bartels, M., van Weegen, F. I., van Beijsterveldt, C. E., Carlier, M., Polderman, T. J., Hoekstra, R. A., & Boomsma, D. I. (2012). The five factor model of personality and intelligence: A twin study on the relationship between the two constructs. Personality and Individual Differences, 53, 368373.Google Scholar
Blanton, H., Buunk, B. P., Gibbons, F. X., & Kuyper, H. (1999). When better-than-others compare upward: Choice of comparison and comparative evaluation as independent predictors of academic performance. Journal of Personality and Social Psychology, 76, 420430.CrossRefGoogle Scholar
Boomsma, D., Geus, E., Vink, J., Stubbe, J., Distel, M., Hottenga, J., . . . Willemsen, G. (2006). Netherlands twin register: From twins to twin families. Twin Research and Human Genetics, 9, 849857.CrossRefGoogle ScholarPubMed
Brewer, M. B., & Weber, J. G. (1994). Self-evaluation effects of interpersonal versus intergroup comparison. Journal of Personality and Social Psychology, 66, 268275.CrossRefGoogle Scholar
Brown, J. D., Novick, N. J., Lord, K. A., & Richards, J. M. (1992). When Gulliver travels: Social context, psychological closeness, and self-appraisals. Journal of Personality and Social Psychology, 62, 717727.CrossRefGoogle Scholar
Buunk, A. P., & Gibbons, F. X. (2006). Social comparison orientation: A new perspective on those who do and those who don't compare with others. In Guimond, S. (Ed.), Social comparison and social psychology: Understanding cognition, intergroup relations, and culture (pp. 1532). New York, NY: Cambridge University Press.Google Scholar
Buunk, B. P., Collins, R. L., Taylor, S. E., Van Yperen, N. W., & Dakof, G. A. (1990). The affective consequences of social comparison: Either direction has its ups and downs. Journal of Personality and Social Psychology, 59, 12381249.Google Scholar
Buunk, B. P., & Ybema, J. F. (1997). Social comparison and occupational stress: The identification-contrast model. In Buunk, B. P. & Gibbons, F. X. (Eds.), Health, coping, and well-being: Perspectives from social comparison theory (pp. 359388). Mahwah, NJ: Erlbaum.Google Scholar
Buunk, B. P., Zurriaga, R., Peíró, J. M., Nauta, A., & Gosalvez, I. (2005). Social comparisons at work as related to a cooperative social climate and to individual differences in social comparison orientation. Applied Psychology, 54, 6180.CrossRefGoogle Scholar
Clark, M. S., Ouellette, R., Powell, M. C., & Milberg, S. (1987). Recipient's mood, relationship type, and helping. Journal of Personality & Social Psychology, 53, 94103.CrossRefGoogle ScholarPubMed
Dobson, A. J., & Barnett, A. (2008). An introduction to generalized linear models (3rd ed.) Boca Raton, FL: Chapman & Hall/CRC Texts in Statistical Science.Google Scholar
Dumas, F., Huguet, P., Monteil, J. M., & Ayme, E. (2005). Context effects in the Stroop task: Knowledge of one's relative standing makes a difference. Current Psychology Letters: Cognition, Brain, & Behavior, 16, 112.Google Scholar
Dumas, F., Huguet, P., Monteil, J.-M., Rastoul, C., & Nezlek, J. B. (2005). Social comparison in the classroom: Is there a tendency to compare upward in elementary school?. Current Research in Social Psychology, 10, 166187.Google Scholar
Ebeling, H., Porkka, T., Penninkilampi-Kerola, V., Berg, E., Järvi, S., & Moilanen, I. (2003). Inter-twin relationships and mental health. Twin Research, 6, 334343.Google Scholar
Festinger, L. (1954). A theory of social comparison processes. Human Relations, 7, 117140.Google Scholar
Fortuna, K., Goldner, I., & Knafo, A. (2010). Twin relationships: A comparison across monozygotic twins, dizygotic twins, and non-twin siblings in early childhood. Family Science, 1, 205211.Google Scholar
Fraley, R. C., & Tancredy, C. M. (2012). Twin and sibling attachment in a nationally representative sample. Personality and Social Psychology Bulletin, 38, 308316.CrossRefGoogle Scholar
Gibbons, F. X., & Buunk, B. P. (1999). Individual differences in social comparison: Development of a scale of social comparison orientation. Journal of Personality and Social Psychology, 76, 129142.Google Scholar
Gilbert, P., Price, J., & Allan, S. (1995). Social comparison, social attractiveness and evolution: How might they be related?. New Ideas in Psychology, 13, 149165.Google Scholar
Huguet, P., Dumas, F., Marsh, H. W., Régner, I., Wheeler, L., Suls, J., . . . Nezlek, J. (2009). Clarifying the role of social comparison in the big-fish-little-pond effect: An integrative study. Journal of Personality and Social Psychology, 97, 156170.Google Scholar
Huguet, P., Dumas, F., Monteil, J.-M., & Genestoux, N. (2001). Social comparison choices in the classroom: Further evidence for students’ upward comparison tendency and its beneficial impact on performance. European Journal of Social Psychology, 31, 557578.Google Scholar
Huguet, P., Galvaing, M. P., Dumas, F., & Monteil, J. M. (2000). The social influence of automatic responding: Controlling the uncontrollable. In Forgas, J. P, Williams, K. D., & Wheeler, L. (Eds.) The social mind: Cognitive and motivational aspects of interpersonal behavior (vol. 2, pp. 371388). Cambridge, UK: Cambridge University Press.Google Scholar
Huguet, P., Galvaing, M.-P., Monteil, J.-M., & Dumas, F. (1999). Social presence effects in the Stroop task: Further evidence for an attentional view of social facilitation. Journal of Personality and Social Psychology, 77, 10111025.Google Scholar
Huguet, P., & Monteil, J. M. (1995). The influence of social comparison with less fortunate others on task performance: The role of gender motivations or appropriate norms. Sex Roles, 33, 753765.Google Scholar
Jonas, K. J., & Huguet, P. (2008). What day is today? A social-psychological investigation into the process of time orientation. Personality and Social Psychology Bulletin, 34, 353365.Google Scholar
Locke, K. D. (2003). Status and solidarity in social comparison: Agentic and communal values and vertical and horizontal directions. Journal of Personality and Social Psychology, 84, 619631.CrossRefGoogle ScholarPubMed
Locke, K. D. (2005). Connecting the horizontal dimension of social comparison with self-worth and self-confidence. Personality and Social Psychology Bulletin, 31, 795803.Google Scholar
Locke, K. D. (2014). Agency and communion in social comparisons. In Krizan, Z. & Gibbons, F. X. (Eds.) Communal functions of social comparison (pp. 1138). Cambridge, UK: Cambridge University Press.Google Scholar
Lockwood, P., & Kunda, Z. (1997). Superstars and me: Predicting the impact of role models on the self. Journal of Personality and Social Psychology, 73, 91103.Google Scholar
Loehlin, J. C., & Nichols, R. (1976). Heredity, environment, and personality: A study of 850 sets of twins. Austin, TX: University of Texas Press.Google Scholar
Luszczynska, A., Gibbons, F. X., Piko, B. F., & Tekozel, M. (2004). Self-regulatory cognitions, social comparison, and perceived peers’ behaviors as predictors of nutrition and physical activity: A comparison among adolescents in Hungary, Poland, Turkey, and USA. Psychology & Health, 19, 577593.Google Scholar
Maccoby, E. E., & Jacklin, C. N. (1974). The psychology of sex differences. Stanford, CA: Stanford University Press.Google Scholar
Major, B., Testa, M., & Bylsma, H. (1991). Responses to upward and downward social comparison: The impact of esteem-relevance and perceived control. In Suls, J., & Wills, T. A. (Eds.) Social comparison: Contemporary theory and research (pp. 237257). Hillsdale, NJ: Erlbaum.Google Scholar
Markus, H. R., & Kitayama, S. (1991). Culture and the self: Implications for cognition, emotion, and motivation. Psychological Review, 98, 224253.Google Scholar
Marsh, H. W., & Hau, K. (2003). Big-fish–little-pond-effect on academic self-concept: A cross-cultural (26 country) test of the negative effects of academically selective schools. American Psychologist, 58, 364376.CrossRefGoogle ScholarPubMed
McGuire, S., & Segal, N. L. (2013). Peer network overlap in twin, sibling, and friend dyads. Child Development, 84, 500511.Google Scholar
Mowrer, E. R. (1954). Some factors in the affectional adjustment of twins. American Sociological Review, 19, 468471.CrossRefGoogle Scholar
Multon, K. D., Brown, S. D., & Lent, R. W. (1991). Relation of self-efficacy beliefs to academic outcomes: A meta-analytic investigation. Journal of Counseling Psychology, 38, 3038.Google Scholar
Mussweiler, T. (2003). Comparison processes in social judgment: Mechanisms and consequences. Psychological Review, 110, 472489.Google Scholar
Mussweiler, T., & Bodenhausen, G. (2002). I know you are but what am I? Self-evaluative consequences of judging in-group and out-group members. Journal of Personality and Social Psychology, 82, 1932.Google Scholar
Mussweiler, T., & Rüter, K. (2003). What friends are for! The use of routine standards in social comparison. Journal of Personality and Social Psychology, 85, 467481.CrossRefGoogle ScholarPubMed
Neale, M. C., Boker, S. M., Xie, G., & Maes, H. H. (2006). Mx: Statistical modeling (7th ed.). Richmond, VA: Virginia Commonwealth University, Department of Psychiatry.Google Scholar
Neyer, F. J. (2002). Twin relationships in old age: A developmental perspective. Journal of Social and Personal Relationships, 19, 155177.Google Scholar
Noller, P. (2005). Sibling relationships in adolescence: Learning and growing together. Personal Relationships, 12, 122.Google Scholar
Noller, P., & Blakely-Smith, A. (2007). Competition and comparison in the relationships of adolescent siblings and twins. Family Relationships Quarterly, 5, 68.Google Scholar
Noller, P., Conway, S., & Blakeley-Smith, A. (2008). Sibling relationships in adolescent and young adult twin and non-twin siblings: Managing competition and comparison. In Forgas, J. P., & Fitness, J. (Eds.), Social relationships: Cognitive, affective, and motivational processes. (pp. 235252). New York, NY: Psychology Press.Google Scholar
Pelham, B. W., & Wachsmuth, J. O. (1995). The waxing and waning of the social self: Assimilation and contrast in social comparison. Journal of Personality and Social Psychology, 69, 825838.Google Scholar
Penninkilampi-Kerola, V. (2005). Co-twin dependence, social interactions, and academic achievement: A population-based study. Journal of Social and Personal Relationships, 22, 519541.Google Scholar
Schunk, D. H. (1989). Self-efficacy and achievement behaviors. Educational Psychology Review 1, 173208.Google Scholar
Segal, N. L. (1984). Cooperation, competition, and altruism within twin sets: A reappraisal. Ethology & Sociobiology, 5, 163177.Google Scholar
Segal, N. L., Graham, J. L., & Ettinger, U. (2013). Unrelated look-alikes: Replicated study of personality similarity and qualitative findings on social relatedness. Personality and Individual Differences, 55, 169174.CrossRefGoogle Scholar
Segal, N. L., Hershberger, S. L., & Arad, S. (2003). Meeting one's twin: Perceived social closeness and familiarity. Evolutionary Psychology, 1, 7095.Google Scholar
Segal, N. L., McGuire, S. A., Miller, S. A., & Havlena, J. (2008). Tacit coordination in monozygotic twins, dizygotic twins and virtual twins: Effects and implications of genetic relatedness. Personality and Individual Differences, 45, 607612.Google Scholar
Segal, N. L., Munson, J. E., Marelich, W. D., Goetz, A. T., & McGuire, S. A. (2014). Meeting of minds: Tacit coordination in adolescent and adult twins. Personality and Individual Differences, 58, 3136.Google Scholar
Seta, J. J. (1982). The impact of comparison processes on coactors’ task performance. Journal of Personality and Social Psychology, 42, 281291.Google Scholar
Spielberger, C. D., Gorsuch, R. L., Lushene, R. E., Vagg, P. R., & Jacobs, G. A. (1970). Manual for the State-Trait Inventory. Palo Alto, CA: Consulting Psychologists.Google Scholar
Stewart, E. A. (2000). Towards the social analysis of twinship. British Journal of Sociology, 51, 719737.Google Scholar
Suls, J., Martin, R., & Wheeler, L. (2002). Social comparison: Why, with whom, and with what effect?. Current Directions in Psychological Sciences, 11, 159163.Google Scholar
Swap, W. C., & Rubin, J. Z. (1983). Measurement of interpersonal orientation. Journal of Personality & Social Psychology, 44, 208219.Google Scholar
Tancredy, C. M., & Fraley, R. C. (2006). The nature of adult twin relationships: An attachment-theoretical perspective. Journal of Personality and Social Psychology, 90, 7893.CrossRefGoogle ScholarPubMed
Taylor, S. E., & Lobel, M. L. (1989). Social comparison activity under threat: Downward evaluation and upward contacts. Psychological Review, 96, 569575.Google Scholar
Tesser, A. (1988). Toward a self-evaluation maintenance model of social behavior. In Berkowitz, L. (Ed.), Advances in experimental social psychology, Vol. 21: Social psychological studies of the self: Perspectives and programs (pp. 181227). San Diego, CA: Academic Press.Google Scholar
Tesser, A., & Schwarz, N. (Eds.). (2001). Intraindividual processes. In Blackwell handbook of social psychology (pp. 436457). Malden, MA: Blackwell.Google Scholar
Thorpe, K. (2003). Twins and friendships. Twin Research, 6, 532535.Google Scholar
Veldkamp, S. A., van Bergen, E., de Zeeuw, E. L., Van Beijsterveldt, C. E., Boomsma, D. I., & Bartels, M. (2017). Bullying and victimization: The effect of close companionship. Twin Research and Human Genetics, 20, 1927.Google Scholar
Watzlawik, M. (2009). The perception of similarities and differences among adolescent siblings: Identification and deidentification of twins and non-twins. Journal of Adolescent Research, 24, 561578.Google Scholar
Wheeler, L., & Suls, J. (2007). Assimilation in social comparison: Can we agree on what it is?. International Review of Social Psychology/Revue Internationale de Psychologie Sociale, 20, 3151.Google Scholar
Wills, T. A. (1981). Downward comparison principles in social psychology. Psychological Bulletin, 90, 245271.Google Scholar
Wood, J. V. (1989). Theory and research concerning social comparisons of personal attributes. Psychological Bulletin, 106, 231248.Google Scholar
Wood, J. (1996). What is social comparison and how should we study it?. Personality and Social Psychology Bulletin, 22, 520537.Google Scholar
Yoon, Y.-S., & Hur, Y.-M. (2006). Twins have slightly higher self-concepts than singletons in the elementary school period: A study of South Korean twins and singletons. Twin Research and Human Genetics, 9, 233239.Google Scholar
Zazzo, R. (1960). Les jumeaux le couple et la personne [Twins as a pair and as individuals] (2 vols.). Oxford, England: Presses Universitaires de France.Google Scholar
Zazzo, R. (1976). The twin condition and the couple effects on personality development. Acta Geneticae Medicae et Gemellologia, 25, 343352.Google Scholar
Figure 0

TABLE 1 Means and Standard Deviations for the Two Versions of the SCO Scale by Zygosity