Borkenau, Riemann, Angleitner, & Spinath (2001) Shared environment – aspects of the environment that are the same for all siblings Nonshared environment – those things that are experienced differently for siblings (e.g. peers, different treatment by parents, etc.)

Borkenau (2001) Reasons that shared environment seems to be unimportant: 1.correlations between adoptive siblings tends to be minimal (around.05), also minimal between adoptees and their adoptive parents 2.Twins reared together are not systematically more similar than twins reared apart. 3.Correlations between MZ tend to be twice as high (or higher) as correlations between DZ twins

Borkenau (2001) Hypothesis: Studies that rely on self-report may underestimate the importance of shared environment due to contrast effects. Contrast effects: twins may influence each other in ways that make their personalities different. E.g. try to emphasize their unique identities May compare themselves to each other rather than population in general when making ratings. This type of rater bias would increase within twin differences.

Previous Observational Studies Generally, lack of shared environmental influence is not as clearly suggested by pervious observational studies as it is by self-report studies. But only a few observational studies done and many involved children, not adults.

Method 300 pairs of adult twins from Germany Took part in a 1 day testing session 234 pairs women, 66 pairs men Ages 18 – 70 years, x = 34

Method continued Took (or had already taken) Costa & McCrae’s NEO-FFI. Had two friends rate them on the peer-report version. Videotaped in 15 settings in which they completed a task. Had blind judges rate the videotapes. All judges rated only one twin and never saw the co-twin.

Tasks Used tasks in which personality differences were likely to be observable: Introduce oneself Arrange three photos in an order and tell an interesting story about the photos Refuse a request for help by a “friend.” Solve a complex problem as fast as possible. Had a confederate solve the same problem in record time. Pantomime uses for a brick Sing a song of one’s choice Had about 60 minutes of videotape per participant (600 hours total)

Ratings Each twin was rated by 4 judges. Each judge saw only one twin. Each team of judges saw different settings (remember bias in ratings in the handshaking study). Provided ratings on 5 point scale of Big Five factors (4 scales for each factor) Randomized order of settings that were rated. Also included ratings of physical attractiveness and likeability.

Results The differences between the reliability coefficients and MZ correlations estimates the contribution of the nonshared environment apart from error of meausrement. r – MZ correlation = nonshared environ. Nonshared environment averages about.35

Results continued Strong evidence for genetic influence as assessed by observational ratings Also support for shared environment as an influence (because DZ correlations were higher than half of MZ correlations) In other words, DZ correlations were higher for these observational measures than for typical self-report measures Findings support idea that there is a contrast effect for DZ twins for self-report personality

Contrast effects in nontwin siblings Saudino et al. (2004) JPSP DZ twins often personalities have negative or zero correlations as rated by parents Puzzling because DZ twins do share some genetic material; but no more alike than random people??? More objective measures show tend to show DZ correlations that are significantly higher. Again, contrast effects

Contrast effects – importance for areas other than twin studies Temperamental research often based on parental ratings Findings may be flawed due to contrast effects This study interested in comparing parental ratings with objective measures for 2 temperament traits

Method 95 sibling pairs Activity measure: monitor device on arm and leg Shyness measure: first 5 min. at lab videotaped –Approach to lab person –Approach to offered toy –Proximity to parent –Clinging to parent –Self-soothing behaviors –Vocalizations –crying

Method continued Parental measures: –Colorado Childhood Temperament Inventory –5 pt. likert scale –Includes shyness and sociability, also activity (and emotionality, persistence) –Child Behavior Questionnaire

Results

Only modest ratings between parent ratings and more objective measures

Results

When parents made global ratings about their child’s temperament behaviors, they rated their children as different (see column 1) Similar findings for global easy/difficult temperament Negative correlations were less prominent when parents made more specific behavioral ratings on the CBQ

Parents tend (at least on some types of ratings) to see their children as having OPPOSING temperaments But siblings do show substantial resemblances when assessed with more objective methods

Birth Rank and Personality Literature: Sulloway (1996) claims systematic and significant effects –First borns more achievement oriented, antagonistic, assertive, conforming, extraverted, organized, planful, responsible, traditional, and identified with parents –Later borns are more adventurous, cooperative, easygoing, empathetic, popular, sociable, rebellious, and unconventional Zajonc (1983) also reports significant birth order effects Ernst & Angst (1983) review same research and make the opposite conclusion

Herrera, Zajonc, Wieczorkowska, Cichomski (2003). Beliefs about birth rank and their reflection in reality, JPSP, 142 – participants rated themselves, first- borns, middle-borns, and last-borns on 11 traits, 45% were first-borns Interested in self-serving biases Interested in influence of birth rank of the raters (participants)

Birth Order

Participants believed that –(a) firstborns are the most intelligent, responsible, obedient, stable, the least emotional, and quite clearly the least creative; –(b) only children are the most disagreeable; –(c) middle-borns are the most envious and the least bold and talkative; and –(d) last-borns are the most creative, emotional, extraverted, disobedient, irresponsible, and talkative. –Also, participants believed that the self exceeded all ranks for agreeableness, intelligence, obedience, responsibility, and stability.

Also found: striking differences between beliefs about the intelligence and creativity of firstborns and last-borns. high intelligence was attributed to firstborns last-borns were believed to be the most creative but not as intelligent. The occupations believed to be held by these ranks were consistent with the personality traits attributed to these ranks. Thus, for example, –firstborns were expected to be lawyers and physicians –last-borns were expected to be artists, actors, musicians, and photographers. –These data indicate that personality traits attributed to the various birth ranks are not simply a matter of a strong positivity bias favoring higher birth ranks but do discriminate among specific traits and abilities.

Also looked at birth order and actual occupational achievement and grade level completed in school. Used a large national sample in Poland

People have definite beliefs that can well qualify as stereotypes about birth rank differences in occupation and personality. these beliefs have a fair correspondence to actual differences in occupational prestige and academic attainment, at least in Poland.

What would you be interested in studying as a follow-up to this study? How would you design and conduct the study? –Hypotheses –Specific method