Environmental Predictors of Personality Differences: A Twin and Sibling Study

Transcription

1 PERSONALITY PROCESSES AND INDIVIDUAL DIFFERENCES Environmental Predictors of Personality Differences: A Twin and Siling Study Philip A. Vernon University of Western Ontario Kerry L. Jang University of British Columia Julie Aitken Harris and Julie M. McCarthy University of Western Ontario Nonshared environmental influences have consistently een shown to account for at least as much of the variance in personality as genetic factors, ut the nature of these nonshared influences has largely remained unidentified. To identify environmental predictors of differential personality development, the Personality Research Form and 4 measures of people's perceptions of their ackground environments were administered to 143 adult twin pairs (93 monozygotic [MZ] and 50 dizygotic [DZ]) and 66 pairs of same-sex nontwin (NT) silings. Differences etween MZ twins, DZ twins, and NT silings in a numer of dimensions of personality were significantly related to differences on the environmental measures, and phenotypic correlations etween the personality and environment measures were themselves entirely attriutale to correlated nonshared Nonshared environmental influences, the life experiences or circumstances not shared y siling? from the same family, have consistently een estimated in ehavioral genetic studies to account for aout as much, if not more, of the variance in personality as genetic factors (Eysenck, 1990; Loehlin, 1989; Plomin, Chipuer, & Loehlin, 1990; Plomin, DeFries, & McClearn, 1990). Just as consistent, however, has een the inaility to identify what these experiences are and how they relate to individual differences in personality (e.g., Plomin & Daniels, 1987). A possile reason for this lack of success was suggested y Plomin and Bergeman (1991), who wrote that most currently availale self-report measures of the environment do not yield an accurate reflection of the exogenous environment. They reasoned that self-report measures of the environment reflect the characteristics of the individuals completing them, ecause people 1 s perceptions of the environment are filtered y their feelings, personality, and cognitions, which get incorporated into their responses to the environmental measure. Plomin and Bergeman (1991) and, more recently, Plomin, Reiss, Hetherington, and Howe (1994) supported this argument y conducting quantitative genetic analyses on a numer Philip A. Vernon, Julie Aitken Harris, and Julie M. McCarthy, Department of Psychology, University of Western Ontario, London, Ontario, Canada; Kerry L. Jang, Department of Psychiatry, University of British Columia, Vancouver British Columia, Canada. Correspondence concerning this article should e addressed to Philip A. Vernon, Department of Psychology, University of Western Ontario, London, Ontario, Canada N6A 5C2. Electronic mail may e sent via the Internet to vernon@sscl.uwo.ca. of popular self-report measures of the environment. They found that most of the measures were sustantially heritale. A genetically influenced environmental measure lurs the distinction etween ehavior and the environment, ecause the same genetic factors may influence oth, as shown y Chipuer and Plomin (1993). Alternatively, an environmental measure free of genetic influence not only would yield a superior description of the exogenous environment ut also would have the potential to provide a clearer explanation of its possile relationship to personality. Earlier research y Daniels (1986), Plomin and Daniels (1987), and Baker and Daniels (1990), relating nonshared environmental influences to individual differences in personality, largely was limited to the use of a single measure of the nonshared environment, namely, the Siling Inventory of Differential Experience (SIDE; Daniels & Plomin, 1985). The SIDE, however, may not adequately characterize the domains of experience not shared y silings. Additionally, the evidence regarding the SIDE as an ojective measure of the exogenous environment is mixed. Daniels and Plomin (1985) initially reported that the SIDE scales showed little genetic influence, ut Baker and Daniels (1990) later showed that many of the SIDE scales did measure heritale traits. The purpose of the present investigation was twofold. The first goal was to estimate the magnitude of the heritale and nonheritale effects on a numer of popular scales of the environment, using a classic twin study design. The second goal was to assess whether differences etween twin and nontwin siling pairs' personalities could e predicted y differences in their responses to the environmental measures. Journal of Personality and Social Psychology, 1997, Vol. 72, No. 1, Copyright 1997 y the American Psychological Association. Inc I4/97/J3 177

2 178 VERNON, JANG, HARRIS, AND MCCARTHY Participants Method Participants were 93 volunteer pairs of adult monozygotic (MZ) twins (74 female pairs, mean age = 23.6 years, SD ~ 7.0; 19 male pairs, mean age = 23.4 years, SD = 5.9); 50 pairs of same-sex adult dizygotic (DZ) twins (41 female pairs, mean age = 24.7 years, SD = 7.4; 9 male pairs, mean age = 24.1 years, SD = 8.5); and 66 pairs of same-sex adult nontwin (NT) silings (51 female pairs, mean age = 23.4 years, SD = 5.2; 15 male pairs, mean age = 22.4 years, SD = 3.5; average age difference = 16.4 months). Zygosity was determined through a questionnaire designed y Nichols and Bilro (1966), which has a reported accuracy of 93%, as compared with the results of lood-typing (Kasriel & Eaves, 1976). Participants were involved in the Western Ontario Twin Project, an ongoing twin and siling study of personality and mental aility, and were recruited y newspaper advertisements. As part of a larger set of questionnaires, participants completed several questionnaires, which are descried here, at their homes and returned them y mail, (a) The SIDE contains 73 items that were scored to yield asolute scores on 11 types of differential experience that may exist etween twins (e.g., Siling Antagonism, Maternal Control, and Peer Delinquency), () The Environmental Response Inventory (ERI; McKechnie, 1974) contains 184 items that form 9 scales rating a person's attitudes toward the physical environment (e.g.. Environmental Adaptation, Environmental Trust, and Antiquarianism). (c) The Family Environment Scale (FES; Moos & Moos, 1986) is a 90-item true-false scale of a person's perceptions of his or her conjugal or nuclear family environment. The scales include, for example, Family Cohesion, Conflict, Moral-Religious Emphasis, and Organization, (d) The Classroom Environment Scale (CES; Trickett & Moos, 1974) contains 90 truefalse items, yielding scores on student perceptions of their classrooms (e.g., Teacher Support, Task Orientation, Order and Organization, and Teacher Control). (e) The Personality Research Form (PRF-E; Jackson, 1986) contains 353 true-false items and yields scores on 20 personality traits (e.g., Aasement, Achievement, Dominance, Harm Avoidance, Nurturance, and Understanding). Heritaility Analyses Monozygotic and DZ raw scale scores were examined for gross departures from normality. Square root or natural logarithm functions were used to otain acceptale symmetry where necessary. McGue and Bouchard (1984) demonstrated that the effects of age and sex can seriously ias heritaility estimates, and scores were corrected y computing standardized residual scores from the multiple regression of each score on age and sex. No mean differences y zygosity were found on any scale (all ps >.05, two-tailed t test). Covariance matrices were computed etween each pair of twins for MZ and DZ pairs separately, with the computer program PRELIS (Joreskog & Sorom, 1989). A model-fitting approach, y means of the computer program LISREL VII (Joreskog & Sorom, 1989a), was applied to these covariance matrices to estimate the proportion of the variance attriutale to additive genetic, shared environmental, and nonshared environmental factors (ACE model). The otained maximumlikelihood parameter estimates of these components (h, c, and e, respectively) were squared to form the familiar h 2, c 2, and e 2 estimates. It is also possile to test for nonadditive genetic effects on those scales where the ratio of the MZ correlation to the DZ correlation is greater than 2. For these scales, a model specifying additive genetic variance, nonadditive genetic variance attriutale to genetic dominance, and nonshared environmental variance was tested (ADE model). The otained maximum-likelihood parameter estimates of these components (h, d, and e, respectively) were squared to form estimates of h 2, d 2, and e 2. Three reduced models were fit that systematically removed one component of variance. The first removed additive genetic effects, the second removed shared environmental effects, and the third removed oth types of effects. A significant change in the chi-square from the full model to the chi-square from a reduced model indicates that the remaining parameters cannot independently account for the variance. The goodness of fit of all models was determined y means of Akaike's (1987) information criterion, AIC = % 2 ~ 2(d/>, which gives a superior indication of fit in models with a small numer of parameters (Bollen, 1989), and y the chi-square itself. Relation of Differential Experience to Differential Personality Differences in the measures of twins' and silings' environments were related to differences in their personality, y computing squared euclidean distance, or squared difference, measures for oth environmental and personality scale profiles, therey providing a quantitative measure of proximity of responses (see Chaplin & Panter, 1993) within each twin pair. Profiles for each of the measures were computed y factor analyzing each scale. The environmental-difference profiles were then entered into multiple regression equations to assess the extent to which they could predict the personality-difference profiles. Results The results are presented in four sections. First, the factor analyses of the environmental scales and of the PRF-E scales are descried. Second, univariate genetic analyses of the environmental and PRF-E scales and factors are presented. Third, analyses investigating relationships etween differences in the environmental factors and differences in the PRF factors are reported. Fourth, multivariate genetic analyses are presented, which investigate the extent to which relationships etween the environmental and personality factors are themselves attriutale to shared genetic or Factor Analyses Each of the four environmental scales (SIDE, ERI, FES, and CES) and the PRF-E were factor analyzed separately y means of principal-components analyses with varimax rotation. Data from all participants (MZ twins, DZ twins, and NT silings) were used in these analyses. Three factors were extracted from the SIDE, accounting for 67.6% of the variance. The first factor (SIDEj) includes items pertaining to siling experiences. The second factor (SIDE 2 ) includes items that involve parental experiences. The third factor (SIDE 3 ) includes peer-experience items. Three factors were also extracted from the ERI scale, accounting for 59.6% of the variance. The first factor (ERI ) includes Pastoralism, Antiquarianism, and Communality. The second factor (ERI 3 ) includes Stimulus Seeking, Environmental Trust, and Mechanical Orientation. The third factor (ERI? ) includes Uranism, Environmental Adaptation, and Need for Privacy (negative loading). These factors were interpreted as representing Preservation (i.e., preservation of natural resources and old uildings), Sensation Seeking-Technology, and Uranism (i.e., enjoyment of city life), respectively. Two factors were extracted from the FES, accounting for 48.9% of the variance. The first factor (FES ) includes Cohesion, Expressiveness, Conflict (negative loading), Independence, Intellectual-Cultural, and Active-Recreational. The second factor (FES 2 ) includes Achievement, Moral-Religious Em-

3 ENVIRONMENTAL PREDICTORS OF PERSONALITY DIFFERENCES 179 phasis, Organization, and Control. These factors correspond to those identified y Rowe (1983) as representing Acceptance- Rejection and Restrictiveness-Permissiveness, respectively. Two factors were extracted from the CES, accounting for 57.9% of the variance. The first factor (CES t) includes Involvement, Affiliation, Teacher Support, and Innovation. The second factor (CES 2 ) includes Task Orientation, Competition, Order and Organization, Rule Clarity, and Teacher Control. These factors were interpreted as representing Interpersonal Relationships, and Goal Orientation and Order, respectively. The factor analysis of the PRF-E scales revealed five factors, accounting for 60.4% of the variance. The first factor (PRFi), with high loadings from Exhiition, Affiliation, Dominance, and Play corresponds to Extraversion. The second factor (PRF 2 ) received high loadings from Order, Cognitive Structure, Achievement, and Impulsivity (negative loading) and was interpreted as Conscientiousness. The third factor (PRF 3 ) had high loadings from Autonomy and Succorance (negative loading) and was interpreted as Autonomy. The fourth factor (PRF 4 ) corresponds to Neuroticism, with high loadings from Defensiveness and Aggression. The fifth factor (PRF 5 ) was interpreted as Openness, having high loadings from Sentience and Understanding. Univariate Genetic Analyses As reported in Tale 1, across the SIDE scales, MZ twin correlations (Pearson product-moment correlations) range from.22 to (median = ), and DZ twin correlations range from.01 to (median = ), indicating few genetic effects on the dimensions tapped y this inventory. Monozygotic twin correlations across the ERI scales range from to (median = ), and the DZ twin correlations range from.02 to (median =.17), indicating the presence of a sustantial genetic influence on most of these scales. Over the FES scales, the MZ twin correlations range from to (median = 5), and the DZ twin correlations range from.06 to (median = 5), indicating that a numer of these scales show a genetic influence. The MZ twin correlations across the CES scales range from to (median =.26), and the DZ twin correlations range from.02 to (median = ), indicating a genetic influence on only a few of these scales. Monozygotic twin correlations on the PRF-E (see Tale 2) range from to (median = ), and the DZ twin correlations range from.01 to (median =.22), indicating a sustantial heritale component for most scales. The full ACE model (or ADE model where appropriate) provided a satisfactory fit to all scales. However, in most cases, reduced models provided a more parsimonious fit. Without exception, the model that allowed for nonshared environmental effects alone could not adequately account for the data from any of the measures. Additive genetic and nonshared environmental effects were sufficient to account for the data from Peer College Orientation from the SIDE; from all scales of the ERI except Environmental Trust; from Family Cohesion, Expressiveness, Achievement, and Active-Recreational Orientation on the FES; and from Task Orientation, Rule Clarity, and Innovation from the CES. Additive genetic and nonshared environmental effects were also sufficient to account for the data from the majority of Tale 1 Pearson Product-Moment Correlations for Monozygotic (MZ) and Dizygotic (DZ) Twins and Heritaility Estimates for Four Environmental Measures Measure h 2 d 2 Siling antagonism 11 Siling caretaking d Siling jealous/ 1 Siling closeness* 1 Maternal affection*' Maternal control a Paternal affection 11 Paternal conirol d Peer college orientation' Peer delinquency* 1 Peer popularity 1 ' Pastoralism c Uranisnr" Environmental adaptation 11 Stimulus seeking 1 ' Environmental trust 11 Antiquariani sm c Need privacy 0 Mechanical orientation 1 Communal ity c Siling Inventory of Differential Experience Family cohesion c Expressiveness" Conflict 3 Independence* Achievement* Intellectual - cultural Active-recreational' Moral-religious emphasis' 1 Organization d Control d Involvement 1 Affiliation 11 Teacher support 11 Task orientation' Competition 11 Order and organization* 1 Rule clarity 1 " Teacher control^ Innovation*" Environmental Response Inventory Familj' Environment Scale Classroom Environment Scale c e Note. All correlations > are significant at p ^.05, two-tailed, h = additive genetic variance; d = nonadditive genetic variance attriutale to genetic dominance; c = shared environmental effects; e = nonshared a The most parsimonious model is the full model comining additive genetic, shared environmental, and nonshared The most parsimonious model is the full model comining additive genetic, nonadditive genetic attriutale to genetic dominance, and nonshared c The most parsimonious model is the reduced model comining additive genetic and nonshared environmental effects. d The most parsimouious model is the reduced model comining shared environmental and nonshared

4 180 VERNON, JANG, HARRIS, AND MCCARTHY Tale 2 Pearson Product-Moment Correlations for Monozygotic (MZ) and Dizygotic (DZ) Twins and Heritaility Estimates for the Personality Research Form Scales Scale Aasement 11 Achievement 8 Affiliation 3 Aggression" Autonomy 8 Change 2 Cognitive structure 1 * Defensiveness 3 Dominance 15 Endurance* Exhiition 3 Harm avoidance" Impulsivity" Nurturance a Order 3 Play 3 Sentience" Social recognition" Succorance" Understanding" Infrequency" Desiraility >"DZ h d 2 c 2 e Note. All correlations > are significant at p ^.05, two-tailed, h = additive genetic variance; d = nonadditive genetic variance attriutale to genetic dominance; c = shared environmental effects; e = nonshared a The most parsimonious model is reduced model comining additive genetic and nonshared The most parsimonious model is the reduced model comining shared environmental and nonshared the PRF E scales, the exceptions eing Aasement, Cognitive Structure, Dominance, and Desiraility. Shared and nonshared environmental effects alone could account for the data from the remainder of the environmental and personality scales, with the exceptions of Maternal Affection from the SIDE, in which the full ADE model provided the est fit; Peer Popularity from the SIDE and Conflict from the FES, in which the full ACE model provided the est fit; and Teacher Control from the CES, in which nonadditive genetic and nonshared environmental factors satisfactorily accounted for the data. As would e expected, the majority of the variance on the SIDE scales was environmental and nonshared in nature, with e 2 ranging from on Peer Popularity to.74 for Siling Jealousy (median = ). Only three SIDE scales showed some additive genetic influence: Maternal Affection (h 2 =.05), Peer College Orientation (h 2 = ), and Peer Popularity (h 2 = ). Maternal Affection also showed nonadditive genetic effects (d 2 = ). Eight of the nine ERI scales showed some additive genetic influence; the median heritaility of all nine scales was. Nonshared environmental effects constituted the ulk of the environmental variance on all ERI scales, ranging from to (median ). Additive genetic influences on the FES scales ranged from.0 to (median =.15). Shared environmental effects were moderate to large on six of the FES scales, ranging from.0 to (median = ). Nonshared environmental effects accounted for the majority of the variance on the FES scales, ranging from to (median = ). Apart from the SIDE, the CES scales showed the least genetic influence, with h 2 ranging from.0 to (median = ). The majority of the variance on the CES was attriutale to nonshared environmental effects, ranging from to.81 (median = ). Typical for personality scales, the additive genetic components on the PRF-E ranged from.0 to, with a median of.45. Nonshared environmental factors accounted for aout as much or more of the variance (median = ) as did additive genetic factors, and shared environmental effects were generally small or nonexistent (median =.0). No nonadditive genetic influence attriutale to genetic dominance was found for any of the PRF-E scales, and the Desiraility scale was the only PRF-E scale that showed sustantial shared environmental variance (c 2 == ). In Tale 3, the results of univariate genetic analyses of the environmental and personality factors revealed similar patterns. Among the SIDE factors, only SIDE 3, representing Peer Experiences, showed any evidence of additive genetic effects; variance on the other two SIDE factors was entirely attriutale to shared and nonshared All three of the ERI factors showed moderate-to-sustantial genetic influence: Two ERI factors (ERI, [Preservation] and ERI 3 [Uranism]) showed predominantly nonadditive effects, and the third (ERI 3 [Sensation Seeking-Technology]) showed only additive genetic effects. None of the ERI factors showed any influence of shared Tale 3 Pearson Product-Moment Correlations for Monozygotic (MZ) and Dizygotic (DZ) Twins and Heritaility Estimates for the Environmental and Personality Factors Factor SIDE, C SIDE;' SIDE 3 ERI, 1 ERI 2 ERI 3 a FES, C FES/ CES^ CES 2 a PRF, PRF 2 PRF 3 PRF 4 PRF 5 a '"MZ >DZ h 2.67 d 2 c 2 e Note. SIDE = Siling Inventory of Differential Experience; ERI = Environmental Response Inventory; FES = Family Environment Scale; CES = Classroom Environment Scale; PRF = Personality Research Frm. All correlations > are p <.05, two-tailed, h = additive genetic variance; d = nonadditive genetic variance attriutale to genetic dominance; c shared environmental effects; e = nonshared environmental effects. Suscript numerals represent factor numers. a The most parsimonious model is the full model comining additive genetic, nonadditive genetic attriutale to genetic dominance, and nonshared The most parsimonious model is the reduced model comining additive genetic and nonshared environmental effects. c The most parsimonious model is the reduced model comining shared environmental and nonshared

5 ENVIRONMENTAL PREDICTORS OF PERSONALITY DIFFERENCES 181 Both of the FES factors and the first CES factor (CES, [ Interpersonal Relationships]) showed no genetic effects. Variance on these factors was entirely attriutale to shared and nonshared The second CES factor (CES 2 [Goal Orientation and Order]) showed nonadditive genetic influence, in addition to the effects of nonshared environmental factors. Finally, variance on all five of the PRF-E factors was est accounted for y genetic and nonshared The first four PRF-E factors showed varying amounts of additive genetic influence, with heritailities ranging from (PRF 3 [Autonomy]) to (PRF, [Extraversion]). The fifth PRF-E factor (PRF 5 [Openness]) showed the influence of sustantial nonadditive genetic effects (d 2 = ). None of the PRF-E factors showed any influence of shared Predicting Personality Differences Squared euclidean distance measures were calculated for each of the factors derived from the four environmental scales and from the PRF-E. Each distance measure was ased on the items corresponding to the factors reported aove for each of the scales. As might e expected, larger differences were found etween NT silings and DZ twins than etween MZ twins on all variales. In no case was there a significant difference etween the magnitudes of the differences etween NT silings and DZ twins. The environmental distance measures were then correlated with the personality distance measures, oth individually (i.e., through zero-order correlations) and in comination (i.e., through multiple regression analyses). For MZ twins, differences in the personality dimension of Autonomy correlated significantly (p <.05) with differences in the ERI Sensation Seeking-Technology (r = ) and Uranism (r =.25) factors. Autonomy differences also correlate with differences in perceived Parental Affection and Control, as assessed y the SIDE (r = ). In addition, differences in the personality dimension of Neuroticism correlated with differences in the ERI Uranism factor (r = ). Similarly, among DZ twins, Autonomy differences correlated with differences on the ERI factors of Sensation Seeking-Technology (r =.68) and Uranism (r =.63) and with differences in SIDE-evaluated Parental Affection and Control (r =.26). Autonomy differences also correlate with differences on the ERI Preservation factor (r = ) among DZs. Among NT silings, differences in all of the personality dimensions except Extraversion correlated with one or more of the environmental distance measures. Conscientiousness differences correlated with differences in ERI Sensation Seeking- Technology (r - ) and in SIDE-evaluated Parental Affection and Control (r =.23). Autonomy differences also correlated with differences in SIDE Parental Affection and Control (r =.22) and, additionally, with differences in CES Interpersonal Relationships (r = ). Differences in Neuroticism correlated with differences in FES Acceptance-Rejection (r = ). Differences in Openness correlated with differences in the ERI Sensation Seeking-Technology factor {r = ). In the multiple regression analyses, each of the 5 personality distance measures was regressed on separate sets of variales, comprising either the 3 SIDE distance measures, the 3 ERI distance measures, the 2 FES distance measures, or the 2 CES distance measures. In addition, each of the 5 personality distance measures was also regressed on all 10 of the environmental distance measures in one set. Each of these analyses was performed separately among the MZ twins, the DZ twins, and the NT silings. Among the MZ twins, only one multiple regression analysis yielded a significant result. This analysis regressed differences in the personality dimension of Autonomy on the three ERI distance measures and yielded an adjusted R 2 of.17, F(3, 59) = 5, p = 3. Although all three ERI measures were entered, only the Sensation Seeking-Technology distance factor had a significant (partial) regression coefficient, f(59) = 3.04, p = 4. Among the DZ twins, three multiple regression analyses yielded significant results. In the first, differences in Autonomy were predicted significantly y differences in the three ERI measures (adjusted R ), F(3, 33) = 4.67, p - 8, although only Preservation had a significant regression coefficient, t(33) = 3, p = 09. In the second analysis, differences in the Conscientiousness personality dimension were also predicted significantly y differences in the three ERI measures (adjusted* 2 = ), F(3, 33) = 10,/? = 01. Only Sensation Seeking-Technology had a significant regression coefficient, r(33) = 2.2, p =.04. In the third analysis, differences in the Conscientiousness dimension were regressed on all 10 environmental distance measures. This analysis yielded a large and significant overall adjusted R 2 of, F(10, 11) = 3,/? =.03, ut none of the individual partial regression coefficients was significant. Among the NT silings, seven multiple regression analyses yielded significant results. Differences on the Conscientiousness dimension were predicted significantly when regressed on all 10 environmental distance measures (adjusted R 2 =.20), F( 10, 41) = 2, p =.03 (only ERI Sensation Seeking-Technology contriuted significantly, ^(41) = 3, p = 2) and when regressed on the 3 ERI distance measures y themselves (adjusted R 2 =.14), F(3, 61) = 4, p = 7 (again, only Sensation Seeking-Technology had a significant regression coefficient, *(61) = 3, p = 09). Differences in Autonomy also were predicted significantly when regressed on all 10 environmental distance measures (adjusted R 2 = ), F(10, 41) , p = 001. Seven predictors had significant regression coefficients: SIDE Siling Experiences, /(41) = -2.92,/? = 6; SIDE Parental Experiences, r(41) = 2.77, p = 9; ERI Preservation, r(41) = -2, p =.04; ERI Sensation Seeking-Technology, r(41) = 3.89, p = 04; FES Acceptance-Rejection, r(41) = -3.06, p = 4; CES Interpersonal Relationships, r(41) = 5.20, p = 001; and CES Goal Orientation and Order, f (41) = -2.98, p = 5. Autonomy differences also were predicted significantly when regressed on the two CES distance measures y themselves (adjusted R 2 =.15), F(2, 59) = 6, p = 3. Only Interpersonal Relationships had a significant regression coefficient, ((59) = 3, p = 07. The other significant multiple regression analyses among the NT silings included the regression of differences in Neuroticism on the 2 FES distance measures. This analysis yielded an adjusted R 2 of.08, F{2 y 62) = 3.92, p =.03, and only Acceptance-Rejection contriuted significantly. Finally, differences in the personality dimension of Openness were predicted significantly, oth when regressed on all 10 environmental distance

6 182 VERNON, JANG, HARRIS, AND MCCARTHY measures (R 2 =.23), F(10, 41) = 2, p =.018 (significant contriutions y CES Goal Orientation and Order, /(41) ~ -2, p =.04, and ERI Sensation Seeking-Technology, r(41) = 3.88, p 04) and when regressed on the three ERI measures y themselves (adjusted R ), F(3, 61) = 4.85, p = 4 (only Sensation Seeking -Technology had a significant regression coefficient, f(61) = 2.73, p = 8). Multivariate Genetic Analyses Given that correlations exist etween some of the environmental and personality measures, the question to e addressed in this section is whether these phenotypic correlations are themselves attriutale to correlated environmental or correlated genetic factors. That is, if a relationship exists, for example, etween the twins' and silings' level of autonomy and their perceived degree of parental affection and control, does this reflect a real environmental correlation, or is it possile that shared genetic factors exert an influence on the correlation etween the two variales? A genetic correlation is unlikely to exist etween these particular variales, ecause the perceived Parental Experiences factor (SIDEa) itself showed no genetic influence (although maternal affection, one of the scales that load on this factor, showed oth additive and nonadditive effects). Relationships etween some of the other environmental and personality measures, individual differences that themselves show genetic influence, might, however, e attriutale to either shared genetic or shared environmental factors (or oth). To address this issue, genetic and environmental correlations were computed, y means of LISREL VII, etween each of the environmental and personality measures differences etween which had shown a phenotypic correlation (as reported in the previous section). In rief, multivariate models specifying correlated additive genetic and nonshared environmental effects indicated no genetic correlation etween any of the environmental and personality variales. Rather, all phenotypic correlations that existed etween these variales were entirely attriutale to correlated nonshared Discussion Vnivariate Genetic Analyses A numer of previous studies showed that environmental measures that is, measures designed to evaluate people's perceptions of their environments are in fact influenced y genetic factors. Plomin, McClearn, Pedersen, Nesselroade, and Bergeman (1988, 1989) and Rowe (1983), for example, reported that a numer of the scales of the FES were heritale; Baker and Daniels (1990) reported a significant genetic influence on silings' perceptions of differential experience as assessed y the SIDE; and Plomin et al. (1994) reported significant genetic effects on 15 of 18 composite measures of the family environment. The present study provides additional support for the notion that individual differences in responses to at least some environmental measures are partly attriutale to genetic factors. Although only 3 of the 11 SIDE scales showed a heritale component (see Tale 1), the third SIDE factor, reflecting peer experiences, was highly heritale (see Tale 3). Moreover, many of the FES scales that had previously een shown to e heritale showed a similar degree of genetic influence in our study. This was particularly true of those FES scales that loaded on the Acceptance-Rejection factor, such as Cohesion, Expressiveness, Conflict, and Active-Recreational. Few of the CES scales showed any genetic influence in the present study, although the CES Goal Orientation and Order factor showed evidence of pronounced nonadditive genetic effects (Tale 3). To our knowledge, this is the first report of a genetic analysis of the CES. Finally, with the exception of the Environmental Trust scale, all of the ERI scales and factors showed moderate to strong genetic influences. The ERI, however, was designed to tap people's attitudes toward the environment. These, in turn, would e expected to reflect aspects of the people's personalities, so it is perhaps not surprising that the ERI was the most highly and the most consistently heritale of the environmental measures used in the present study. Environmental Predictors of Personality Differences The zero-order and multiple correlations found etween differences in the twins' and silings' perceptions of their environments and differences in their personalities are of considerale interest. Few previous studies have een ale to identify features of the nonshared environment that contriute to differential personality development in twins and silings, despite the fact that most personality traits typically show a pronounced influence of these nonshared factors. Of the five personality factors extracted from the PRF-E, Autonomy was oth the least heritale (Tale 3) and the most consistently predictale y factors derived from the environmental measures. Among MZ twins, DZ twins, and NT silings, differences in Autonomy correlated with differences on the ERI and on the SIDE. Among the NT silings, differences in Autonomy also showed a strong multiple correlation (R 2 - ) when regressed on the 10 environmental distance measures, and factors derived from all 4 of the environmental measures (i.e., from the SIDE, ERI, FES, and CES) contriuted significantly to this correlation. These include Siling and Parental Experiences from the SIDE, Acceptance-Rejection from the FES, and Interpersonal Relationships and Goal Orientation and Order from the CES, all of which might reasonaly have een expected to contriute to the development of autonomy. With the exception of Extraversion, which was one of the more highly heritale of the personality traits, differences on each of the other factors extracted from the PRF were also predictale y some of the environmental distance measures. Of particular interest were the findings that among the NT silings, differences in Neuroticism correlated with differences in FES Acceptance-Rejection, and differences in Conscientiousness correlated with differences in perceptions of Parental Affection and Control. Both of these correlations seem quite reasonale from a psychological point of view. Overall, this study demonstrated that differences etween twins and NT silings, in several orthogonal dimensions of personality, are correlated with differences in a numer of family and ackground environmental measures. Moreover, even though oth the personality and some of the environmental measures were themselves influenced y genetic factors, the correla-

7 ENVIRONMENTAL PREDICTORS OF PERSONALITY DIFFERENCES 183 tions etween them were shown to e entirely attriutale to correlated Across all of the personality and environmental distance measures, significant zero-order correlations ranged etween.25 and among MZ twins, etween.26 and.68 among DZ twins, and etween.22 and,42 among NT silings. Multiple regression analyses showed that etween 8% and 51% of the variance in personality differences etween DZ twins or NT silings could e accounted for y differences in their environments; the only significant multiple regression analysis among the MZ twins yielded an i? 2 of.17 etween differences in Autonomy and differences on the ERI factors. As would e expected, those personality factors whose differences showed the most and the largest correlations with the environmental distance measures were also those that showed the lowest heritaimes and the largest influence of the nonshared environment. These included Autonomy (h 2 = ),Conscientiousness (h 2 = ), and Neuroticism (h 2 = ), which etween them showed a total of 13 significant correlations with the environmental distance measures (9 of these involved Autonomy). In contrast, differences in the more highly heritale Openness (h 2 = ) and Extraversion (h 2 = ) factors yielded only 1 significant correlation with differences in environments. Conceivaly, one reason that few previous studies have een successful in finding relationships etween differences in personality and differences in family and ackground environments may e that the personality traits that they investigated were among the more highly heritale. In sum, three main conclusions may e drawn from the present study: First, individual differences in responses to a variety of environmental measures show the influence of genetic factors. 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Classroom Environment Scale manual Palo Alto, CA: Consulting Psychologists Press. Received Octoer 30, 1995 Accepted April 6, 1996