Personality and Coping: A Study of Twins Reared Apart and Twins Reared Together

Transcription

1 Behavior Genetics, Vol. 35, No. 2, March 2005 (Ó 2005) Personality and Coping: A Study of Twins Reared Apart and Twins Reared Together Kenji Kato 1,*, and Nancy L. Pedersen 1,2 Received 20 Nov Final 30 July 2004 The relative importance of genetic and environmental factors for stress coping styles, age and gender differences, and the relationship between coping styles and personality traits were assessed in middle-aged and older adult twins reared apart and reared together, as part of the ongoing Swedish Adoption/Twin Study of Aging (SATSA). The Billings and Moos Coping Measure was administered to 1339 individual twins (in 446 intact pairs). The mean age was 58.0 ± Moderate genetic influences and significant gender differences in variance estimates were found for the three coping scales (Problem Solving, Turning to Others, and Avoidance). Turning to Others and Avoidance in women also showed shared rearing environmental influences. In contrast, no age differences in variance estimates were found in this sample. Multivariate model fitting indicated that genetic influences on adults coping differentially reflect genetic factors in common with personality traits. The sources of covariation also showed significant gender differences. KEY WORDS: Coping; gender difference; personality; twins. 1 Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden. 2 Department of Psychology, University of Southern California, Los Angeles, California, USA. * To whom correspondence should be addressed at Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, P.O. Box 281, SE , Stockholm, Sweden. Tel: Fax: Kenji.Kato@meb.ki.se 147 INTRODUCTION Coping strategies are cognitive, behavioral or physiological processes aimed at diminishing or terminating stress. While adaptive coping can ameliorate the consequences of stress, maladaptive coping strategies can lead to an increased risk for chronic diseases such as high blood pressure, diabetes, and heart disease (Maes et al., 1996). Furthermore, extremes in coping styles can influence susceptibility to psychiatric disorders, particularly depression and certain anxiety disorders. Understanding individual differences in coping therefore may have implications for prevention or intervention. Despite the considerable attention to coping in the psychological literature in the last two decades, very few studies have been conducted thus far that have explicitly focused on genetic and environmental sources of individual differences in coping. Coping is a multidimensional construct that is not adequately represented by a single measure, and numerous inventories to assess coping have been proposed (Schwarzer and Schwarzer, 1996). Although little agreement exists regarding the optimal conceptualization of coping, a problem-focused and emotion-focused terminology has been frequently used among researchers (Lazarus, 1993). In addition, factor-analytic studies of coping have repeatedly identified three factor solutions such as problem solving, seeking support, and avoidance (Amirkhan, 1990), task-oriented, emotion-oriented, and avoidance-oriented (Endler and Parker, 1990), or cognitive self-control, solace seeking, and ineffective escapism (Rohde et al., 1990). There is a growing amount of evidence that indicates the importance of personality dispositions in predicting and explaining variance in coping style /05/ /0 Ó 2005 Springer Science+Business Media, Inc.

2 148 Kato and Pedersen and its consequences (Costa et al., 1996). Some consensus has been reached supporting the use of the five-factor model as a framework for research on the relationship between personality and coping (e.g., McWilliams et al., 2003; O Brien and DeLongis, 1996). In particular, Neuroticism and Extraversion have been prominent in the literature, owing largely to Hans Eysenck s influential work (Costa et al., 1996). For example, Neuroticism is associated with self-blaming, wishful thinking, becoming passive and withdrawn, whereas Extraversion is correlated with talking, positive thinking, and restraint. Although less prominent, there is also some evidence that Openness to Experience is related to specific coping styles (Costa et al., 1996). People with high Openness to Experience rethink the problem and seek for new information. It is reasonable to speculate that individual differences in coping styles reflect individuals different personality dispositions. Gender may be a potential source of individual differences in coping styles. Gender differences in mean levels have been broadly reported in the stress and coping literature (Beasley et al., 2003). For example, in their study of depressed patients, Billings and Moos (1984) found that women used emotional discharge more frequently than men. The greater depressiveness of women might be due partly to their less effective coping (Hanninen and Aro, 1996). In addition, age could also be an origin of individual differences in coping. Findings about age differences in mean levels are, however, complex and puzzling. Some studies have suggested that differences in coping exist among young, middle-aged, and elderly persons (e.g., Aldwin, 1991), however, the strength and direction of the age-coping association was not clear (Strack and Feifel, 1996). A longitudinal study revealed no consistent age-related differences in the use of coping (McCrae, 1989). In any case, finding differences in means does not necessarily imply differences in variation. To scrutinize the origins of individual differences, one must employ study designs with genetically informative samples, such as twin, adoption, or family studies. There has been a surprisingly limited number of behavioral genetic studies on stress coping. Kendler et al. (1991) reported the first results of behavioral genetic analysis on coping among young adult female twins (mean age 29 ±8 years). Mellins et al. (1996) also investigated coping among schoolaged twins. In addition, Busjahn et al. (1999) reported results among young adult twins (mean age 34 ± 14 years). These three studies all show evidence of genetic influences on most coping scales. To date, however, no study has been reported concerning genetic and environmental influences on coping in middle age or an older adult sample. Considering the putative effects of adaptive and maladaptive coping on health status or the severity of physical and psychiatric diseases, it would be worthwhile to broaden our knowledge of individual differences in coping with an older and larger sample with both genders. To explore the sources of variance in adults coping, the present study employed an adoptive twin study design. This study is part of the ongoing Swedish Adoption/Twin Study of Aging (SATSA, Pedersen et al., 1991), a substudy of the Swedish Twin Registry (Lichtenstein et al., 2002; Pedersen et al., 2002). The uniqueness of SATSA is that it combines the twin and adoption study designs, by including twin pairs who were separated in their early childhood (twins reared apart) as well as twin pairs who were reared in the same family (twins reared together). Inclusion of twins reared apart permits differentiation between influences of the environment shared during the rearing period (shared rearing environment) and those contributing to similarity even after separation (correlated environment). Considering that coping styles have proved to be heritable in children and younger adults, we hypothesized that coping styles would be heritable in middle-aged and older adults. The literature also led us to postulate that shared environmental influences on coping would be limited, and the majority of the variance would be of the non-shared variety. Because so little is known about gender differences in genetic and environmental factors for coping, it is difficult to propose hypotheses concerning gender differences in the present study. However, it is not unlikely that there are gender differences in these factors, in that such differences have been reported in other SATSA studies of health and stress-related phenotypes (Finkel et al., 2003; Gatz et al., 1992; Lichtenstein and Pedersen, 1995; Pedersen et al., 1989; Saudino et al., 1997) as well as by others (e.g., Bierut et al., 1999; Kendler et al., 2001). As mentioned above, personality dispositions are likely to play an important role in predicting variance in coping. It is also true that numerous studies have demonstrated genetic influences on personality traits throughout the lifespan (Eaves et al., 1989; Loehlin, 1992). Further, there is some evidence that genetic influences on personality are

3 Personality and Coping 149 important for other purported measures related to environmental responses (Saudino et al., 1997). Thus, given these considerations, it is possible that at least some of the genetic influence for coping, if such variance exists in middle-aged and older adults, are attributable to genetic factors for personality. METHODS Participants This study is part of the ongoing SATSA (Pedersen et al., 1991), which is a longitudinal program of gerontological genetics. The SATSA sample is a subset of the population-based Swedish Twin Registry (Lichtenstein et al., 2002; Pedersen et al., 2002). SATSA consists of same-sex twins who were separated before age 11 and reared apart and a sample of twins who were reared together matched on gender, age, and county of birth. Participants in SATSA received mail-out questionnaires in 1984, 1987, 1990, and Details on SATSA were described elsewhere (Pedersen et al., 1991). The present data were gathered during the third wave of questionnaires sent in October This was the only occasion of SATSA that included a coping measure. Of 1339 individual twins who responded to the questionnaire, both members of 58 pairs of MZ (monozygotic) twins reared apart, 101 pairs of MZ twins reared together, 147 pairs of DZ (dizygotic) twins reared apart, and 140 pairs of DZ twins reared together responded to the questions on stress coping. The sample consisted of 795 women (59.4%) and 544 men (40.6%). The mean age of the twins was 58.0 ± 12.8 as of January 1, 1990, and 71.9% of the pairs were over 50 years of age. The mean ages of female and male twins were 58.6 ± 13.4 and 57.1 ± 12.0, respectively. In the analysis of age differences in variance estimates, the twins were classified into two subgroups cut at the median age of the pair respondents (58.19 years old) so that the pair respondents can be equally distributed in these two subgroups. The mean ages of younger subgroup and older subgroup were 45.8 ± 8.2 and 67.5 ± 5.8, respectively. Zygosity was determined on the basis of a series of questions regarding physical similarity, such as During childhood, were you and your twin partner as alike as two peas in a pod? and How often did strangers have difficulty in distinguishing between you and your twin partner when you were children? Measures Stress coping Stress coping was measured with a 33-item questionnaire based on Billings and Moos (1984). All the items were in Swedish. Table I shows the back translation of the questionnaire. Responses were recorded on a four-point Likert-type frequency scale. The options were:never, Seldom, Now and then, andoften. Confirmatory factor analyses were performed first by using PROC CALIS procedure in SAS version 8 (SAS Institute, 2002) for the purpose of testing the Billings and Moos structure of coping scales. Exploratory factor analysis was then carried out by the method of principal components with promax rotation using the PROC FACTOR procedure in SAS. Single respondents and one randomly selected twin of each pair were used in the exploratory factor analysis. Components that had eigenvalues greater than 1.0 were selected. In subsequent analyses, all available data (both single respondents and pair respondents) were used. Additional confirmatory factor analyses were performed by using Mx (Neale et al., 1999) in order to check whether non-independence of twin pair observations distorted the factor solution that was obtained above. Unit weight scale scores were formed by assigning each item to the component on which the item loaded most heavily (Table I). Items with factor loading under 0.30 were omitted in the summation of scale scores, resulting in 27 items in total. For individuals who missed responding to one item for a particular scale, the missing value was substituted by the mean of the rest of the individual s responses for the particular scale. Individuals having more than one missing item for a particular scale were excluded from the calculation of scale scores. Personality Extraversion and Neuroticism traits were measured by a short form of the Eysenck Personality Inventory (EPI, Eysenck and Eysenck, 1975), which has been widely used in Scandinavian twin studies (Floderus-Myrhed et al., 1980; Pedersen et al., 1988; Viken et al., 1994). Each scale score was based on the sum of 0 and 1 (No Yes) responses to nine

4 150 Kato and Pedersen Table I. Items of Stress Coping Questionnaire and Factor Loadings Item Factor loading Problem Solving 1. I try to find out more about the situation I try to see it from the positive side I make a plan of action and follow it I consider alternative solutions for handling the problem I rely on my past experience since I was in a similar situation before I take things one at a time I try to step back from the situation and be more objective I think through the situation in order to understand it better I try not to act hastily or follow my first hunch I know what must be done and I make an effort to make things work I compromise to get something positive from the situation Turning to Others 2. I talk with my spouse or other relative about the problem I talk with a friend about the problem I seek help, for example, from a doctor, lawyer or clergyman I discuss my feelings with others I take it out on others when I get angry or depressed I let my feelings out in one way or another I seek help from others with similar experiences Avoidance 6. I prepare for the worst I tell myself things that help me feel better I get away from things for a while I avoid being with people on the whole I promise myself that things will be different next time I refuse to believe that it happened I accept that what is is; nothing can be done I try to reduce tension by eating more I try to reduce tension by taking more tranquilizing drugs Note: The instrument starts with the statement When I have a problem/feel stressed... items. Openness to Experience was measured by a shortened version of the NEO-Personality Inventory (NEO-PI, Bergeman et al., 1993; Costa and McCrae, 1985). The six items of this scale were scored on a five-point Likert-type frequency scale ranging from 1 (strongly agree) to 5 (strongly disagree), and then summed for a total score. which parameters should be included in subsequent structural equation modeling. In the calculation of intraclass correlations, only the pair respondents were included and a double-entry technique was used in order to avoid possible bias introduced by non-random assignment of twins as twin A or twin B. Statistical Analyses Equality of variances was tested between MZ and DZ twins or twins reared apart and reared together by using PROC TTEST procedure in SAS. Intraclass correlations The intraclass correlations for MZ and DZ pairs were calculated to provide an indication of Univariate model fitting Maximum likelihood model fitting analyses were performed to estimate genetic and environmental factors influencing the coping scales. In the present study, the models were based on the following structural equations for the four rearing-by-zygosity groups, namely, MZ twins reared apart (MZA) and reared together (MZT), and DZ twins reared apart (DZA) and reared together (DZT):

5 Personality and Coping 151 COV MZA ¼ A þ C; COV MZT ¼ A þ S þ C; COV DZA ¼ 1=2A þ C; COV DZT ¼ 1=2A þ S þ C; where COV is the covariance between twin pairs, A is additive genetic variances, S is shared rearing environmental variances, and C is correlated environmental variances. Because our sample has both reared apart and reared together twins, we can differentiate between shared rearing environmental influences and correlated environmental influences. The latter refers to all twin similarity which cannot be explained by genetic influences or shared rearing environmental influences. Examples of correlated environmental influences would be similarities in rearing environments despite being in different homes (selective placement), similarities in adult life experiences, and post-separation contact. We performed model fitting by using raw data of the coping scales separately for men and women with age as a moderator (definition) variable, and for younger and older subgroups with gender as a moderator variable. All twins were included in the analyses, regardless of the response status of the cotwin. Maximum-likelihood estimates of the parameters and model-fit statistics such as v 2 value and Akaike s Information Criterion (AIC, Akaike, 1987) were calculated by using Mx. Age and gender differences in genetic and environmental influences were tested as follows:in the first series of analyses, we allowed all the parameters to be estimated separately by gender or by age-group. In the second series of analyses, we constrained these parameters to be equal across men and women or across younger and older subgroups, and compared the unconstrained full model and the nested constrained model. A significant difference in v 2 goodness-of-fit indicates that the constrained (nested) model fits the data worse than the full model. In the third series of analyses, specific parameters were dropped. Among the nested models which fit the data, the best-fit model was chosen by using AIC, which reflects both the goodness-of-fit and parsimony of the model. Multivariate Model Fitting Multivariate model fitting analyses were carried out to explore the extent to which genetic and environmental factors that influence personality traits also are important for coping styles. In each model, we included one of the three coping scales and the personality scales that were significantly (p < 0.05) correlated with that particular coping scale for both men and women. Cholesky decomposition models consisting of these variables were fitted to the raw data by using Mx. Age was included in the models as a definition variable. The same multivariate models were run for men and women. First, we allowed all the parameters to be estimated separately by gender. We then constrained these parameters to be equal across men and women, and compared the unconstrained full model and the nested constrained model. The importance of genetic factors in common to coping and the personality measures was tested by dropping the oblique paths. The importance of environmental covariance was tested in a similar fashion. Best-fit models were selected using AIC criteria. RESULTS Factor Analysis The v 2 fit of confirmatory factor analysis for the Billings and Moos structure was (df = 339). In the exploratory factor analysis, three factors were identified by the traditional eigenvalue criteria. Each item of the questionnaire was assigned to the factor-derived scale on which the item loaded most heavily (Table I). Because the difference in fit functions of confirmatory factor analyses using SAS suggested that our model fits better than the Billings and Moos structure (Dv 2 = 203.7, Ddf = 18), we disregarded their classification and employed our own terminology. Additional confirmatory factor analyses using Mx did not indicate distorted factor solution due to non-independence of twin pair observations. The first factor, labeled Problem Solving, reflected a positive, practical coping. The second factor, labeled Turning to Others, reflected coping by seeking support from others. The third factor, labeled Avoidance, reflected a negative, escapist coping. Table I shows the assignment of items to factors. Chronbach s alphas for Problem Solving, Turning to Others, and Avoidance were 0.82, 0.73, and 0.68, respectively. The promax-derived interfactor correlations were 0.40 between Problem Solving and Turning to Others, 0.16 between Problem Solving and Avoidance, and 0.07 between Turning to Others and Avoidance. Scale scores of these factors were mod-

6 152 Kato and Pedersen erately correlated: 0.40 between Problem Solving and Turning to Others, 0.24 between Problem Solving and Avoidance, and 0.20 between Turning to Others and Avoidance. All the correlation coefficients were significantly greater than zero at p < Total variances did not significantly differ for MZ and DZ twins and for twins reared apart and reared together in both men and women, except Turning to Others in men, indicating the fulfillment of a basic assumption for the twin method. Variances for Turning to Others for DZ and for twins reared apart in men were significantly greater than those for MZ and for twins reared together, respectively. The difference will reduce the fit of structural models in the case of this scale. Intraclass Correlations The intraclass correlations for each of the four rearing-by-zygosity groups by gender are shown in Table II. The correlations for MZ twins were consistently greater than those for DZ twins, suggesting moderate genetic influences for all the three scales. The intraclass correlations for MZ twins reared together were less than twice those for DZ twins reared together in women, suggesting correlated environmental contributions to twin similarity. of total variation for additive genetic (A), shared rearing environmental (S), correlated environmental (C), and non-shared environmental (E) components of variance. Change in goodness-of-fit statistics from the full model is also shown in the right-hand columns of the table. When the model was constrained to be equal across men and women, the goodness-offit was worsened significantly for all the three scales, indicating significant gender differences in the relative importance of genetic and environmental parameters. For Avoidance, the estimated additive genetic variation for women was substantially larger than that for men. Correlated environments were estimated as zero for all scales. Shared rearing environments were significant for Turning to Others and Avoidance in women. When the model was constrained to be equal across younger and older subgroups, none of the goodness-of-fit statistics was worsened significantly (Dv 2 = 5.02, Ddf = 4, p = 0.29, AIC = 2.98 for Problem Solving; Dv 2 = 6.52, Ddf = 4, p = 0.16, AIC = 1.48 for Turning to Others; and Dv 2 = 6.15, Ddf = 4, p = 0.19, AIC = 1.85 for Avoidance). These results suggest no age differences in parameter estimates for the three coping scales. We therefore focused on gender differences in subsequent multivariate analyses. Univariate Model Fitting Results of model fitting for the three coping scales by gender are summarized in Table III, with goodnessof-fit statistics, parameter estimates, and percentages Table II. Intraclass Correlations for Coping Scales by Gender, Zygosity, and Rearing Status Men Women MZA MZT DZA DZT MZA MZT DZA DZT Problem Solving n Turning to Others n Avoidance n Note: n = number of pairs; MZA = monozygotic twins reared apart; MZT = monozygotic twins reared together; DZA = dizygotic twins reared apart; DZT = dizygotic twins reared together. *p < 0.05; **p < Multivariate Model Fitting Table IV shows the phenotypic correlations between the coping scales and the personality scales (Neuroticism, Extraversion, and Openness to Experience) by gender. In general, high scores in Problem Solving and Turning to Others were positively correlated with high scores in Openness to Experience and Extraversion. High scores in Avoidance were correlated with high scores in Neuroticism and with low scores in Extraversion. The choice of scales to be included in the multivariate models was based on these results. Genetic and environmental factors to be included in each model were based on the results of the preceding univariate analyses. That is, AE model was tested for all scales in men and Problem Solving in women, whereas ASE model was tested for Turning to Others and Avoidance in women. Figures 1, 2, and 3 illustrate the best-fit models for the association between coping scales and their correlated personality scales by gender. For Problem Solving (Figs. 1a and 1b), genetic

7 Personality and Coping 153 Table III. Estimates of Percentages of Total Variation (95% CI) and Goodness-of-fit Statistics for Coping Scales by Gender Men Women Changes from full model Factors A S C E A S C E )2ln(L) Dv 2 Ddf p AIC Problem Solving 1. Full model 0.30 ( ) 0.00 ( ) 0.00 ( ) 0.70 ( ) 0.29 ( ) 0.07 ( )0.14 ( ) 0.50 ( ) Men and women 0.38 ( ) 0.01 ( ) 0.04 ( ) 0.57 ( ) equated 3. Best-fit model 0.30 ( ) 0.70 ( ) 0.51 ( ) 0.49 ( ) )4.08 Turning to Others 1. Full model 0.21 ( ) 0.00 ( ) 0.00 ( ) 0.79 ( ) 0.40 ( ) 0.16 ( )0.00 ( ) 0.44 ( ) Men and women 0.37 ( ) 0.06 ( ) 0.00 ( ) 0.56 ( ) equated 3. Best-fit model 0.21 ( ) 0.79 ( ) 0.40 ( )0.16 ( ) 0.44 ( ) )6.00 Avoidance 1. Full model 0.15 ( ) 0.00 ( ) 0.00 ( ) 0.85 ( ) 0.48 ( ) 0.14 ( )0.00 ( ) 0.38 ( ) Men and women 0.34 ( ) 0.06 ( ) 0.02 ( ) 0.58 ( ) equated 3. Best-fit model 0.15 ( ) 0.85 ( ) 0.48 ( ) 0.14 ( ) 0.38 ( ) )6.00 Note: A = additive genetic effect, S = shared rearing environmental effect; C = correlated environmental effect; E = non-shared environmental effect; 2 ln(l) ¼ 2 times the natural log likelihood; df = degrees of freedom; AIC = Akaike s information criterion. Table IV. Phenotypic Correlations between Coping Scales and Personality Scales Personality scales Coping scales Neuroticism Extraversion Problem Solving Turning to Others Openness to Experience Men Women Men Women Avoidance Men Women Note: *p < 0.05; **p < variation was entirely explained by one genetic factor in common to Openness to Experience in the best-fit model in men (Dv 2 = 2.05, Ddf = 4, p = 0.73, AIC = 5.95), whereas the full model fit best in women. For Turning to Others (Figs. 2a and 2b), the best-fit model had no genetic factor in common across the three scales in men (Dv 2 = 1.93, Ddf = 3, p = 0.59, AIC = 4.07), whereas a common genetic factor and a unique factor were included in the best-fit model in women (Dv 2 = 1.76, Ddf = 4, p = 0.78, AIC = 6.24). For Avoidance (Figs. 3a and b), genetic variation was entirely explained by two genetic factors in common to Neuroticism and Extraversion in men (Dv 2 = 0.59, Ddf = 1, p = 0.44, AIC = 1.41), whereas a common genetic factor as well as a unique factor remained in the best-fit model in women (Dv 2 = 1.65, Ddf = 6, p = 0.95, AIC = 10.36). When all the paths were constrained to be equal across gender, the constrained (nested) models fit significantly worse than the unconstrained full models (Dv 2 = 51.20, Ddf = 11, p < for Problem Solving; Dv 2 = 70.88, Ddf= 17, p < for Turning to Others; and Dv 2 = 73.79, Ddf = 18, p < for Avoidance), suggesting gender differences in patterns of covariation between personality and coping. Of the total genetic variation of each coping scale, the genetic factor unique to coping accounted for 0% for Problem Solving and Avoidance in men, 68% for Avoidance in women, 83% for Problem Solving in women, 90% for Turning to Others in women, and 100% for Turning to Others in men.

8 154 Kato and Pedersen Fig. 1. The best-fit model for the association between personality scales and Problem Solving in (a) men and (b) women. A = additive genetic factor; E = non-shared environmental factor. Figure 4 presents estimates of genetic and environmental contributions to the phenotypic correlations between each coping scale and personality scale. Genetic contributions were calculated by multiplying path coefficients of the genetic factors common to both the personality scale and the coping scale and summing them. Environmental contributions to the phenotypic correlation were calculated in a similar fashion. The consistency of the estimated with the observed phenotypic correlation suggests the adequacy of our models for capturing the associations between personality and coping. DISCUSSION The present study represents one of the first attempts to examine genetic and environmental influences on coping in middle-aged and older adult sample, gender differences in those influences, and multivariate analyses of the relationship between coping styles and personality traits. There were significant gender differences in the relative importance of genetic and environmental influences on coping scales. Variances for the coping scales in women were more attributable to genetic influences than in men. Relatively high correlations were found between Problem Solving, Turning to Others, and Openness to Experience, as well as between Avoidance, Neuroticism, and Extraversion. These associations were moderately or substantially due to genetic influences in both men and women, except Turning to Others in men. It is noteworthy that similar coping styles were found in our study and two of the other twin studies (Kendler et al., 1991; Mellins et al., 1996), despite different coping questionnaires and different types of samples. In these three twin studies, the coping scales were derived from factor analyses. The three coping strategies we obtained were similar to the scales that Kendler et al. found in young women. Similarly, our coping scales were analogous to what Mellins et al. found regarding children s coping:our Turning to Others seems to be equivalent to their Use of Parents and Use of Peers, while our Avoidance is similar to their Distraction. In terms of problem-focused and emotion-focused coping, the former seems to be close to our Problem Solving, and the latter seems to be close to our Avoidance. As noted by Kendler et al. and Mellins et al., Turning to Others could be interpreted as both problem-focused (seeking for informational support) and emotion-focused (seeking for emotional support) coping strategy. Genetic and Environmental Influences on Coping As we hypothesized, significant genetic influences were found for all three coping strategies except Avoidance in men. Furthermore, the shared rearing environment showed only limited influence, which was found in Turning to Others and Avoidance in women, whereas correlated environmental influences (which reflect selective placement or postseparation contact) were not observed in our results. In general, our results are consistent with the previous twin studies on coping, with moderate heritability, limited influences of shared environment, and substantial influences of non-shared environment. We were the first to assess and find significant gender differences in the relative importance of genetic and environmental influences on coping.

9 Personality and Coping 155 Fig. 2. The best-fit model for the association between personality scales and Turning to Others in (a) men and (b) women. A = additive genetic factor; S = shared rearing environmental factor; E = non-shared environmental factor. Fig. 3. The best-fit model for the association between personality scales and Avoidance in (a) men and (b) women. A = ;additive genetic factor; S = shared rearing environmental factor; E = non-shared environmental factor. All the three coping scales showed differences in the magnitude of genetic influences between men and women. In addition, moderate but significant shared rearing environmental influences were found for Turning to Others and Avoidance in women. As mentioned previously, gender differences in variance estimates are relatively common in behavior genetic studies, particularly for health-related indicators (Finkel et al., 2003; Lichtenstein and Pedersen, 1995). In our study of Type A-like measures (Pedersen et al., 1989), a scale Pressure showed gender differences, with shared rearing environmental effects only in women. Also, Saudino et al. (1997) reported that genetic influences on measures of stressful life events were found only in women. Further, Gatz et al. (1992) found that genetic effects for a scale Depressed Mood appeared to be stronger in women than in men. Given the considerable differences in prevalence of stress-related health problems such as depression, the results of the present study as well as our previous studies would suggest that these phenotypic differences reflects different mechanisms of stress perception and response across gender. Because our SATSA participants comprise same-sexed pairs, we cannot speculate whether the consistent findings of gender differences in variance estimates reflect differences in genes operating in the coping styles for men and women.

10 156 Kato and Pedersen Fig. 4. Genetic and environmental contributions to the phenotypic correlations between personality scales and coping scales by gender. Note that the phenotypic correlations between Extraversion and Avoidance were reversed in order to facilitate the interpretation of the figure. N = Neuroticism; E = Extraversion; O = Openness to Experience; PS = Problem Solving; TO = Turning to Others; AV = Avoidance. In contrast, we did not find age differences in genetic and environmental influences on coping in these middle-aged and older adults. Our results do, however, differ somewhat from Kendler et al. (1991) who observed shared environmental influences instead of genetic influences on their denial measure, whereas their turning to others did not show shared environmental influences. On the other hand, Mellins et al. (1996) found no genetic influences on their Problem Solve but found shared environmental influences. With cross-sectional data, it is impossible to disentangle whether these inconsistencies represent age-related changes or cohort or study differences. Longitudinal data are therefore warranted in order to distinguish cohort effects from aging effects in coping. Unfortunately, the coping measure was only assessed at one occasion in SATSA. Coping Styles and Personality Traits As we hypothesized, genetic influences on coping scales were partly attributable to genetic factors in common with one or two personality traits, except Turning to Others in men. The results suggest that individual s coping styles to some extent reflect his or her personality, in part due to the influences of the common genetic factors. Uehara et al. (1999) reported that extraversion and frustration tolerance were significantly related to task-oriented coping, and neuroticism was associated with emotion-oriented coping in depressive outpatients. While the participants of the present study were not depressive, our results go further and demonstrate that those associations are partly attributed to genes that personality and coping styles have in common. Busjahn et al. (2002) found common genetic variation between Emotional Coping and blood pressure and linkage between Active Coping and b-2 adrenergic receptor gene, suggesting a role of this gene in the relationship between psychological and physiological phenotypes. Although the present study is cross-sectional and therefore causality is not obvious, our results may provide some implication that the covariation between personality and coping is mediated by the pleiotropic function of genes. In multivariate analyses, we further found that the patterns of covariation between personality and coping scales were considerably different in men and women. As seen in Figure 4, the relative importance of genetic and environmental contributions to the phenotypic correlations also differed by gender. In general, best-fit models in women showed more complex patterns of association. On the other hand, genetic covariation for Problem Solving and for Avoidance in men was entirely accounted for by one or two genetic factors in common with personality. These findings suggest that the role of personality in determining coping strategies is gender-specific and strategy-specific, and that women s coping is likely to be influenced by more factors that are distinct from genetic effects on personality.

11 Personality and Coping 157 Thus, at least for women, coping and personality are distinct constructs but show systematic associations. This distinction is notable given that both coping and personality (Neuroticism in particular) are important predictors of health outcomes. Limitations Our method relied on self-report of the subjects, without specifying any situation. As Lazarus (1993) pointed out, this might mislead subjects to answer preferred responses instead of their actual coping styles. Self-report may also result in spurious associations among the measures due to shared method variance. However, the consistency of the present study and previous studies where situations were specified may assure the validity of our results. As often discussed in the literature on stressful life events (e.g., Kendler et al., 2001), gender differences might be caused by the differences in the recall and reporting of their behavior, not in their real action or responses. 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