OBJECTIVE. Recent studies have noted personality differences among adult survivors of very preterm birth, including higher neuroticism and cautiousness and lower extraversion. We attempted to replicate and extend these recent studies by examining personality characteristics across multiple components of personality that traditionally define personality structure in a birth cohort of young adults born at extremely low birth weight (501–1000 g), the smallest and most at-risk infants.
PARTICIPANTS AND METHODS. We assessed 71 (76% of the original birth cohort) extremely low birth weight and 83 (74% of the original cohort) term normal birth weight young adults by using well-validated personality measures, indexing 4 traditional components of personality: temperament (Cheek and Buss shyness and sociability and Eysenck neuroticism and extraversion), motivation (Carver and White behavioral inhibition and behavioral activation), cognitive and affective (Coopersmith self-esteem and University of California, Los Angeles, loneliness), and socialization (Eysenck psychoticism and lie). All of the participants were right-handed and free of neurosensory and psychiatric impairments.
RESULTS. Extremely low birth weight adults reported significantly higher shyness, behavioral inhibition, and socialization (a measure of prosocial behavior defined by risk aversion and adherence to societal mores) and lower sociability and emotional well-being than their normal birth weight counterparts, replicating and extending the findings of previous studies.
CONCLUSIONS. Young adults who were born at extremely low birth weight and without major impairments are more cautious, shy, and risk aversive and less extraverted than their normal birth weight counterparts, possibly placing them at risk for future psychiatric and emotional problems.
It is now well established that extremely low birth weight (ELBW) (<1000 g) and very low birth weight (VLBW) (<1500 g) infants are at substantial risk for a wide spectrum of neurosensory impairments, learning difficulties, behavioral and emotional problems, and poorer general health than normal birth weight (NBW) control participants.1–8 In previous studies, we have shown that parents of ELBW children are more likely than parents of NBW control participants to report the occurrence of attention-deficit/hyperactivity disorder symptoms (including inattention and hyperactivity) at ages 5,9 7 to 8,10 and 12 to 16 years.11 Research has indicated that ELBW children may also present with subtle difficulties in psychosocial functioning, such as a lower level of social competence, than VLBW children or term control subjects. 12 However, one issue that has received relatively little attention is whether socioemotional and personality processes are affected in adults born at extremely low birth weight.
Hack et al13 found significantly lower scores on measures of risk taking and antisocial behavior among a VLBW sample when compared with a matched control group. More recently, Allin et al14 found that adults born very preterm (VPT) reported significantly lower extraversion and higher neuroticism and lie (ie, social desirability) scores on the Eysenck Personality Inventory. VPT adults had a personality style characterized by increased behavioral inhibition and negative affectivity and decreased sensation seeking and positive affectivity, placing them at risk for mental health problems.14 Overall, these findings are also consistent with other research indicating high levels of anxiety and depression1 and reduced self-esteem2 among VLBW adolescents, although not all studies show differences in self-esteem among ELBW survivors.15
The purpose of the present study was to compare the personality characteristics of adults born at ELBW and NBW across multiple components of personality that traditionally define personality structure. Each of these components is known to contribute to risk for different emotional problems.16 The ELBW cohort in the present study has been followed longitudinally since birth and tested on a broad range of outcomes at key developmental ages.3–6,9–11,15 In the present study, we sought to replicate and extend earlier work in at least two ways. First we focused on a regional cohort of ELBW survivors that may constitute a more vulnerable sample than VLBW or VPT survivors examined in previous studies.13,14 Such a sample overcomes some of the possible sample selection mechanisms associated with including only referrals or survivors from a single center. Second, we examined multiple components of personality (ie, temperament, motivation, cognitive and affective component, and socialization) that are known to define personality structure in addition to the those examined in recent studies of adults born VLBW or VPT.13,14 By examining multiple components of personality, the establishment of a more accurate picture of how individual differences in personality style may place individuals at risk for different psychiatric problems is possible. On the basis of earlier studies,1,2,13,14 we predicted that adults born ELBW would report higher shyness, behavioral inhibition, and socialization (ie, a measure of prosocial behavior defined by risk aversion and adherence to societal mores) and lower sociability and emotional well-being than their NBW counterparts.
Participants and Sample Overview
The ELBW cohort was composed of 397 predominantly white infants (birth weight: 501–1000 g) born between 1977 and 1982 to residents of a geographically defined region in central-west Ontario, Canada, and recruited at birth. Of these 397 infants, 179 (45%) survived to hospital discharge from the NICU; there were 13 late deaths, and in total 166 survived to young adulthood. By design, we chose to constitute a fairly homogeneous group of participants and, therefore, excluded individuals with neurosensory impairments (n = 46), psychiatric problems (n = 2), and those who were not right-handed (determined by using the Edinburgh handedness scale; n = 25). The adults born ELBW were followed longitudinally from birth, and neurosensory impairments (cerebral palsy, blindness, deafness, mental retardation, and microcephaly) were diagnosed by a neonatologist and a developmental pediatrician. We selected only right-handed individuals, because participants in the present study were part of a larger studying examining regional electroencephalographic asymmetry correlates of emotional processing, and left-handers are thought to differ in the lateralization of emotion. Accordingly, left-handers were excluded from this study. Of the 93 adult survivors of ELBW eligible to participate, 7 were lost to follow-up, 4 refused the entire young adulthood study, and 11 either refused or were unable to be recalled to the laboratory. A total of 71 (76%) of 93 eligible adult survivors of ELBW participated in the study.
The NBW control group was composed of 145 individuals who were selected from a random sample of children born at term and obtained from class lists of 8-year-old children from several Hamilton Public School Boards and matched for race, gender, and socioeconomic status with the ELBW cohort.10 The control participants were not followed prospectively from birth. Of the 145 NBW control participants originally enrolled, we excluded those with neurosensory impairment (n = 3), nonright-handed individuals (n = 27), and those who had epilepsy and multiple sclerosis at young adulthood (n = 2). Of the 113 eligible NBW control participants, 4 were lost to follow-up, 7 refused the entire young adulthood study, and 19 either refused or were unable to be recalled to the laboratory. A total of 83 (74%) of 113 NBW adults participated in the study. The 154 ELBW and NBW participants in the present study were part of a larger study examining transition into young adulthood,17 health states,18 and quality of life19 of individuals born with ELBW.
Carver and White Behavioral Inhibition/Behavioral Activation Scales
The behavioral inhibition scale (BIS)/behavioral activation scale (BAS) is a 20-item scale that measures dispositional sensitivities of 2 motivational systems: a behavioral inhibition or withdrawal system and a behavioral activation or approach system.20 Sample items from the scale include, “I worry about my mistakes” (BIS), and, “When I see an opportunity for something I like, I get excited right away” (BAS). Each item is scored on a 4-point Likert scale, ranging from 1 (“very true for me”) to 4 (“very false for me”). Lower scores on the BIS scale indicate increased inhibition, and lower scores on the BAS scale indicate increased activation. The score for the BAS scale is a composite of 3 subscales: drive (“When I want something, I usually go all-out to get it”), reward responsiveness (“It would excite me to win a contest”), and fun seeking (“I crave excitement and new sensations”). Psychometric data for the BIS/BAS are presented elsewhere.20
Cheek and Buss Shyness and Sociability Scale
The Cheek and Buss shyness and sociability scale is a 10-item scale that is used to index shyness and sociability.21,22 Of the 10 items, 5 items index shyness, and 5 items index sociability. Sample items from the shyness scale include, “I find it hard to talk to strangers,” and, “I feel inhibited in social situations.” Sample items from the sociability scale include, “I like to be with people,” and “I find people more stimulating than anyone else.” Each item is rated on a scale from 0 (“extremely uncharacteristic”) to 4 (“extremely characteristic”). The Cheek and Buss Shyness and Sociability Scale has excellent reliability and validity properties.22,23
Coopersmith Self-esteem Scale
The Coopersmith self-esteem scale is a 25-item self-report measure answered on a dichotomous scale (“like me” or “not like me”).24 Sample items from the Coopersmith self-esteem scale include, “I often wish I was someone else,” and “I'm a lot of fun to be with.” The relevant reliability and validity data for the scale have been presented by Coopersmith.24
Eysenck Personality Questionnaire-Revised Short Form
The Eysenck Personality Questionnaire-Revised Short Form (EPQ-RS) is a 48-item questionnaire that is used to measure the personality dimensions of neuroticism, extraversion, and psychoticism.25,26 Sample items from the separate scales include, “Do you ever feel ‘just miserable’ for no reason?” “Are you a worrier?” (neuroticism: a predisposition to anxiety), “Are you a talkative person?” “Can you usually let yourself go and enjoy yourself at a lively party?” (extraversion: a predisposition to sociability), “Would being in debt worry you?” and “Do you enjoy co-operating with others?” (psychoticism: a predisposition to antisocial behavior). The EPQ-RS also includes a lie scale, which is a measure of social desirability. Sample items from the lie scale include, “Are all your habits good and desirable ones?” and “Have you ever said anything bad or nasty about anyone?” All of the items are answered either “yes” (1) or “no” (0), and the scores are subsequently summed to derive a total for each of the 4 subscales. The EPQ-RS is a psychometrically sound measure with ample test-retest reliability and internal consistency.25,26
Revised-University of California, Los Angeles, Loneliness Scale Loneliness Scale
The Revised-University of California, Los Angeles (R-UCLA), loneliness scale is composed of 20 items, which are answered on a 0 (“extremely uncharacteristic”) to 4 (“extremely characteristic”) metric.27 Sample items include, “I lack companionship,” and “I feel left out.” Reliability and validity are reported in Russell et al.27
All of the personality measures were collected in the McMaster University Child Emotion Laboratory under the supervision of trained research staff. On arrival to the laboratory, the procedures were explained to the participants, and written informed consent was obtained. All of the procedures were approved by the McMaster University Health Sciences Research Ethics Board. The study was conducted from 2001 to 2004.
Personality data were missing from 1 ELBW participant who did not complete any of the personality measures. This ELBW participant was, therefore, excluded from additional analyses. In addition, 2 participants (1 ELBW and 1 NBW) did not complete the R-UCLA loneliness scale.
Sociodemographic Data for the ELBW and NBW Groups
The mean birth weight of the ELBW cohort was (mean ± SD) 874 ± 11 g and 3395 ± 470 g for the NBW cohort; the corresponding gestational ages were 27.5 ± 2.2 weeks and term, respectively (Table 1). There were no significant differences in the parental socioeconomic or educational status of the ELBW and NBW cohort (the P values were >.05). The mean age at assessment was 23.3 ± 1.4 years for ELBW and 23.6 ± 1.1 years for NBW and did not differ between groups (P > .05).
We computed theoretically and empirically derived composite measures that reflect 4 different traditional components of personality: temperament, motivation, cognitive/affective components, and socialization. Given that the individual personality measures were scaled differently, we first z-scored them, and then computed the 4 composite measures to index the 4 different components of personality. The individual measures that were used to compute each composite measure were interrelated (P < .05).
The temperament component was composed of 2 measures: shyness (Cheek and Buss shyness + EPQ-RS neuroticism measures) and sociability (Cheek and Buss Sociability + EPQ-RS extraversion); the motivation component was composed of 2 measures: behavioral inhibition (BIS measure) and behavioral activation (BAS: drive + reward responsiveness + fun-seeking measure); the cognitive/affective component composed 1 measure: emotional well-being (Coopersmith self-esteem + reversed R-UCLA loneliness); and the socialization component was composed of 1 measure: socialization (reversed EPQ-RS psychoticism + EPQ-RS lie). The socialization component reflects a measure defined by cautiousness, risk aversion, and adherence to social mores.
Separate analyses of variance, with group (ELBW or NBW) and gender (male or female) as the between-subject factors, were performed on each of the composite measures. There were no significant interactions with gender (P > .05), so gender was collapsed in all of the subsequent analyses. We then performed separate independent t tests with group (ELBW and NBW) as the between-subject factor on each of the measures reflecting the 4 components of personality structure. The analyses revealed significant main effects for group on each of the 4 components of the personality structure (see Table 2).
As predicted, the ELBW group self-reported significantly higher shyness (t151 = 2.32; P = .022) and lower sociability (t151 = −2.11; P = .037) and emotional well-being (t149 = −1.96; P = .052) and higher socialization (t151 = 3.41; P = .001) than the NBW group. As predicted, the ELBW group also self-reported higher behavioral inhibition (t151 = 1.85; P = .067) than the NBW group, although this difference only approached statistical significance. There were no significant main effects for group on the BAS measure (P > .05).
As can also be seen in Table 2, the effect sizes ranged from .30 (small) to .56 (medium). These effect sizes were similar to recent findings of adults born very prematurely,14 which reported effect sizes ranging from .38 to .39 on the same (Eysenck Personality Questionnaire) or conceptually similar personality measures as the ones used in the present study.
A series of Pearson correlations were also computed between the continuous measure of birth weight (in grams) and the adult personality measures within the ELBW group (see Table 3). As can be seen in Table 3, lower birth weight, overall, was associated with higher shyness (r = −0.20; P < .05), behavioral inhibition (r = 0.16; P = .05), loneliness (r = −0.17; P < .05), and lie (r = −0.26; P < .01) scores and with lower psychoticism (r = 0.17; P < .05) scores.
We found that young adults born at ELBW differed across multiple components of personality that traditionally define personality structure compared with their NBW peers. As predicted, the ELBW young adults reported higher shyness, behavioral inhibition, and socialization (ie, a measure of prosocial behavior, reflecting cautiousness, risk aversion, and adherence to social mores) and lower sociability and emotional well-being than NBW adults. These between-group effects were not gender specific. That is, the results were not accounted for by ELBW males or females only but were applied to the group as a whole. We also found significant correlations between birth weight and personality characteristics within the ELBW group. Lower birth weight was associated with higher shyness, behavioral inhibition, loneliness, and lie scores (ie, a measure of social desirability) and lower psychoticism scores (ie, a predisposition toward antisocial behavior). Overall, these results replicate and extend those of other recent studies, which have noted higher neuroticism and lie scores and decreased extraversion scores in a sample of VPT young adults compared with control participants and lower risk taking and lower antisocial behavior in VLBW adults compared with their NBW control participants.13,14,28,29
It is also important to point out that we failed to find any significant interaction effects between group and gender on personality. In contrast, the results of previous studies have indicated that the higher neuroticism and behavioral cautiousness found in premature or low birth weight samples were largely accounted for by female participants.13,14,29 One possible reason that we did not find gender effects was that ELBW may constitute a more extreme sample than the VLBW samples used in other studies. The lack of gender differences raises the possibility of a threshold effect. That is, gender and birth weight may interact on personality but only at certain birth weights. The ELBW group may be a more vulnerable group than the VPT or VLBW groups, and the risk level because of birth weight alone may be strong enough for the development of a particular personality style overshadowing any potential influences because of gender. Another possibility is that, unlike other studies, we excluded left-handed individuals and those with neurosensory impairments, because the present study was part of a larger study examining regional electroencephalographic correlates of emotion in ELBW adults, and it is thought that left-handers are known to differ in the cerebral lateralization of emotion. Because these exclusion criteria are known to interact with gender, it is possible that we excluded potential gender differences by virtue of our design. However, the proportion of male and female participants who were left-handed and excluded or right-handed and included did not differ.
What do differences in personality among ELBW adults reflect? Personality can be modeled as a dynamic system that is responsive to a variety of factors, both genetic and learned-environmental, as well as to the probabilistic functions within gene-gene30 and between gene-environment31 interactions. Perturbations in the early developmental stages of socioemotional and personality processes can bias their subsequent trajectories. Extreme prematurity is a neonatal stress factor that may constitute such a perturbation. Our results suggest that ELBW may be a risk factor for the development of a personality style that is characterized by cautiousness, withdrawal tendencies, and negative affectivity. This personality style is also characterized by a decreased probability to engage in some social situations and subsequently an increased chance of experiencing loneliness and lowered emotional well-being, possibly placing them at risk for psychiatric problems. However, caution is warranted: we have also shown that ELBW adults in this cohort seem to have similar peer, partner, and family relationships compared with their NBW peers.32 Interestingly, the cautious personality style found among the ELBW adults may simultaneously function as a protective factor against the reduction of impulsive and antisocial tendencies, as observed by others28,29,33 as well as by us in our cohort.32 Other reasons for lower risk-taking behavior may be the result of an increase in parental monitoring and/or lack of opportunities because of developmental lags or disabilities in ELBW survivors.34
The results of the present study have theoretical implications. The study of personality development over the last two decades has focused largely on dispositional arguments in typically developing homogenous populations in which natural variability and genetics are the primary explanations used for understanding individual differences in personality.35,36 These views assume that individual differences in behavioral inhibition and shyness arise from innate biological predispositions present at birth. These dispositions are largely genetically programmed and biologically based, although modifiable through experience.30,35,36 Much of this work has focused on the ways in which similarities in initial conditions (biological systems) lead to a specific outcome (behavioral inhibition). The results of the present study challenge these existing explanations by providing an alternative hypothesis to the development of behavioral inhibition and shyness resulting from early life events.
There are reliable sources of evidence from human and nonhuman animal studies that exposure to stress prenatally, perinatally, or early postnatally can have a profound influence on social and affective development.37 The present results are in line with this hypothesis. Shyness and timidity and the emergence of a cautious personality style may result from early life events because of stress rather than solely innate predispositions, raising the concept of equifinality. Equifinality is a concept whereby different early experiences (ie, innate genetic or biological predispositions versus early stress) may lead to a common final outcome (ie, shyness). That is, some typically developing children may start off life cautious and timid because genetic or biological predispositions point them in that direction without having been exposed to early stress. Other children who begin life with severe stress may also manifest a similar cautious behavioral style as some healthy children as a result of early life events.
Although the present study was a longitudinal, population-based study that included the smallest and most at-risk infants, it is not without limitations. First, our return rate for both groups was slightly lower than in our previous studies.6,17–19 Second, the personality measures used were subjective in nature. Although the psychometric properties for the personality measures used in our study are well documented, self-report measures are still susceptible to methodologic limitations and participant biases in reporting. It is possible that the participants may not have fully comprehended the questions that we were asking them, they might have been limited by the response options available, or they may not have been completely candid in answering the questions.
Development is a dynamic process in which fluctuations in initial conditions might be capable of altering the long-term trajectories of psychobiological systems, placing some adults born at ELBW at risk for psychiatric problems. Our study highlights the need to consider multiple components of personality and how early stress can impact the developmental sequela of socioemotional and personality processes. Future research should examine the potential differences between ELBW and NBW groups on more objective theoretically derived behavioral (eg, measures of direct behavioral observation in stressful situations) and psychophysiological (eg, measures of electrocortical and cardiovascular responses in resting and stressful situations) measures that are known to index underlying personality and socioemotional processes in addition to the subjective self-report measures used herein.
This research was supported by the Social Science and Humanities Research Council of Canada grant 410-02-1663 (awarded to Dr Schmidt), a predoctoral fellowship from the Natural Sciences and Engineering Research Council of Canada (awarded to Mr Miskovic under the direction of Dr Schmidt), and Canadian Institutes of Health and Research grant MOP42536 and National Institute of Child Health and Human Development grant 1-RO1HD40219 (awarded to Dr Saigal and her colleagues).
We thank the participants for continued cooperation; Lindsay Bennett, Sylvia Nowakowski, Caroline Parkin, and Diane Santesso for help with data collection; and Barbara Stoskopf and Lorraine Hoult for organizing the assessments.
- Accepted February 20, 2008.
- Address correspondence to Louis A. Schmidt, PhD, McMaster University, Department of Psychology, Neuroscience, and Behaviour, 1280 Main St West, Hamilton, Ontario, Canada L8S 4K1. E-mail:
The authors have indicated they have no financial relationships relevant to this article to disclose.
What's Known on This Subject
Extreme prematurity is associated with risk for socioemotional and psychiatric problems developmentally.
What This Study Adds
This study replicates and extends previous research by examining different components of personality in adults born at extremely low birth weight, which places them at risk for different psychiatric problems.
- ↵Saigal S, Hoult LA, Streiner DL, Stoskopf BL, Rosenbaum PL. School difficulties at adolescence in a regional cohort of children who were extremely low birth weight. Pediatrics.2000;105 (2):325– 331
- ↵Taylor HG, Hack M, Klein N. Attention deficits in children with < 750 gram birthweight. Child Neuropsychol.1998;4 (1):21– 34
- ↵Saigal S, Pinelli J, Hoult L, Kim MM, Boyle M. Psychopathology and social competencies of adolescents who were extremely low birth weight. Pediatrics.2003;111 (5 pt 1):969– 975
- ↵Ross G, Lipper EG, Auld PA. Social competence and behavior problems in premature children at school age. Pediatrics.1990;86 (3):391– 397
- ↵Allin M, Rooney M, Cuddy M, et al. Personality in young adults who are born preterm. Pediatrics.2006;117 (2):309– 316
- ↵Saigal S, Lambert M, Russ C, Hoult L. Self-esteem of adolescents who were born prematurely. Pediatrics.2002;109 (3):429– 433
- ↵Pervin LA, John OP, eds. Handbook of Personality: Theory and Research. New York, NY: Guilford Press;1999
- ↵Saigal S, Stoskopf B, Boyle M, et al. Comparison of current health, functional limitations, and health care use of young adults who were born with extremely low birth weight and normal birth weight. Pediatrics.2007;119 (3). Available at: www.pediatrics.org/cgi/content/full/119/3/e562
- ↵Saigal S, Stoskopf B, Pinelli J, et al. Self-perceived health-related quality of life of former extremely low birthweight infants at young adulthood. Pediatrics.2006;118 (3):1140– 1148.
- ↵Cheek JM. The Revised Cheek and Buss Shyness Scale. Wellesley, MA: Wellesley College;1983.
- ↵Coopersmith S. The Antecedents of Self-esteem. San Francisco, CA: Freeman;1967
- ↵Eysenck, HJ, Eysenck SBG. Eysenck Personality Scales (EPS Adult). London, United Kingdom: Hodder and Stroughton;1991
- ↵Hack M, Youngstrom EA, Cartar L, et al. Behavioral outcomes and evidence of psychopathology among very low birth weight infants at age 20 years. Pediatrics.2004;114 (4):932– 940
- ↵Schmidt LA, Fox NA, Hamer DH. Evidence for a gene-gene interaction in predicting children's behavior problems: association of 5-HTT short and DRD4 long genotypes with internalizing and externalizing behaviors in seven year-old children. Dev Psychopathol.2007;19 (4):1103– 1114
- ↵Fox NA, Nicols K, Henderson H, et al. Evidence for a gene-environment interaction in predicting behavioral inhibition in middle childhood. Psychol Sci.2005;16 (12):921– 926
- ↵Saigal S, Stoskopf B, Pinelli J, Boyle M, Streiner D. Social functioning, peer, partner and family relationships and satisfaction with life. Presented at the Pediatric Societies' Annual Meeting; May 14–17, 2005; Washington, DC; E-PAS2005:57 :2125
- ↵Cooke RW. Health, lifestyle, and quality of life in young adults born very preterm. Arch Dis Child.2004;89 (3):201– 206
- ↵Kagan J. Galen's Prophecy: Temperament in Human Nature. New York, NY: Basic Books1994
- ↵Kagan J. The concept of behavioral inhibition. In: Schmidt LA, Schulkin, J, eds. Extreme Fear, Shyness, and Social Phobia: Origins, Biological Mechanisms, and Clinical Outcomes. New York, NY: Oxford University Press;1999:3– 13
- ↵Schulkin J, Schmidt LA, Erickson K. Glucocorticoid facilitation of corticotropin- releasing hormone in the placenta and the brain: functional impact on birth and behavior. In Powers M, Schulkin J, eds. Birth, Distress and Disease: Placenta-Brain Interactions. Cambridge, United Kingdom: Cambridge University Press;2005:235– 267
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