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This is to certify that the

thesis entitled

.Rredicting Sibling Personality‘
‘Differences from Non-Shared
Environmental Factors

presented. by

Tammy Lynn Mann

has been accepted towards fulfillment
of the requirements for

MA Clinical Psychology

degree in

 

 

  

 

Major professor

Date gl/C/7Q

0-7639 MS U is an Affirmative Action/Equal Opportunity Institution

 

 

 

 

PLACE N RETURN BOX to move this checkout from your record.
TO AVOID FINES return on or before duo due.

 

DATE DUE DATE DUE DATE DUE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

MSU Is An Alfirmattve ActloNEqml Opportunity Institution

 

 

PREDICTING SIBLING PERSONALITY DIFFERENCES
FROM NON-SHARED ENVIRONMENTAL FACTORS

By

Tammy Lynn Mann

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF ARTS

Department of Psychology

1990

ABSTRACT

PREDICTING SIBLING PERSONALITY DIFFERENCES
FROM NON-SHARED ENVIRONMENTAL FACTORS

BY

Tammy Lynn Mann

This study examined the extent to which non-shared
environmental factors could predict sibling personality
differences in comparison to selected family constellation
variables (i.e., sex, age, birthorder). The participants
were 100 biologically related sibling pairs less than four
years apart in age. Half were university resident
Introductory Psychology students while their siblings
resided elsewhere, usually at home. Their separate
responses to the Sibling Inventory of Differential
Experience (SIDE) assessed non-shared environmental
factors, and personality variables were similarly assessed
by the Emotionality Activity Sociability (EAS) Inventory.
The correlations of siblings' EAS responses were generally
weak and statistically nonsignificant (median same-sex
; - .06) consistent with data obtained in prior studies.
Contrary to the central hypothesis, the family
constellation variables tended to correlate more firmly
with sibling EAS differences than did the non-shared
environmental factors. Limitations and implications of the

findings were discussed.

ACKNOWLEDGEMENTS

I thank God for giving me the strength and ability to
complete this project. Special thanks to my parents and my
dear husband for their consistent support and
encouragement. I would also like to thank Dr. John Hurley,
my advisor, for all of his much needed support and
guidance.

iii

TABLE OF CONTENTS

Page(s)
Iii-St Of Tables 0 O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O C 0v
IntrOduction. O O O O O O O O I O O O O O O O I O O O O O O O O O O O O O O O .0 O O O O O 1

Review of Relevant Literature......................2-10
Hypotheses.0.0.0.0000000000000000.00.0.0000....010

MethOdOOOOO...0.000.000...OCOOCOOOOOCCCCCCOCCIOCOC.11-15
sample. . C O O . C C . C C C O O O O O C O O O O C C C C C C C C C C C . . C C O O C C C 11-12
' Instruments. 0 O C C O C O O O O O O C O C C O O O O O O O C C C C C C C O C O C C C 12-14
Procedures . O O C O C C C C O C C C C C C C O C C C O C O C O O O C C O O O C C . C C 14-16
Results. 0 O C C C C C C O O C C O O O O O O O O O O O O O O O O O O C O O O O O O O O O O C C 17-25
DiSCUSSion/ConCJ-us1ons . C C O O O O O C O O O O O O O O O C C O O O C C O C O C 26-30
Appendices. . C O C C C C C O . O O O C C C O C C O C C O C O O O O O C O O O O C O C O O C 33-45
Appendix A, Personal Data Sheet.................33
Appendix 8, Statement of Informed Consent.......35

Appendix C, Form utterOOOOOOOOOOOOOOOOOOOOO0.0038-.39

Appendix D, Mailed Statement of Informed
consentOOO.COO...OOOOOOOOOOOOOOOOOOOOOOO0......41

Appendix E, Debriefing Note.....................43

Appendix F, Tables 3 & 4, Social Desirability
as it Relates to SIDE and EAS Scales..........45

List Of ReferenceSOIOOOOOO0.0.0.0...0.0.0.00000000047—48

LIST OF TABLES

Page

Table 1, Means and Standard Deviations for

EASOO0....0.0....0.0.0.0.000...00.000.00.00...0.0.17

Table 2, Means and Standard Deviations for SIDE
scales...O0..O0.0...OO00......OOOOOOOOOOOOOOOOOOO.19

Table 3, EAS Scale and Marlowe-Crowne Social
Desirability Scale Correlations...................45

Table 4, SIDE Scale and Marlowe-Crowne Social
.Desirability Scale Correlations...................45

Table 5, EAS Scale Difference Scores Between
Sibling PairSOOCOOOOOO0..0....0.0.0....0000000000021

Table 6, Means and Standard Deviations for
SIDE Scales (Sibling Pair Averages)...............21

Table 7, EAS Correlations Between Sibling Pairs......22

Table 8, Personality Difference Scores and
Constellation Variables...........................23

Table 9, EAS Difference Scores and
Sibling InteractionOOOOOOOOOO00.0.00...00.0.0.0...24

Table 10, EAS Difference Scores and
Perceived Parental Treatment......................24

Table 11, EAS Difference Scores and
Peer Group characteristics........................25

It seems logical to believe that siblings who grow-up
in the same home environment, exposed to the same parents
and community, should resemble each other in terms of
personality. After all, early experiences, especially in
the home, are thought to be related to subsequent .
development. While that may seem plausible, empirical
evidence suggests that siblings are not very similar on a
variety of personality variables. This study will examine
this issue by exploring aspects of environmental
experiences that are different for sibling pairs which may
help understand the development of dissimilar personalities

between siblings.

BEIIB!_Q£_BEL£!AEI_LITEBAIHEB
Nearly 50 years ago Woodworth (1941) proposed that

siblings in the same family are likely to develop quite
different personality styles. Crook's (1937) earlier study
reported an average sibling correlation of .12 for
personality resemblance using the Bernreuter Personality
Inventory. The magnitude of sibling resemblance
correlations reported in Crook's study is similar to those
being reported currently. Plomin and Daniel's (1987)
review examined studies which suggested .16 as the average
non-twin sibling correlation for personality variables.
Based on Scarr and Grajek's (1982) review of studies in
this area, the degree of sibling resemblance on personality
measures typically ranges from .15 to .20 for biologically
related non-twin siblings.

Dixon and Johnson (1980) described research conducted
in Hawaii which reported average sibling correlations
ranging from .03 to .19 when investigators utilized four
different instruments measuring personality (Cattell's
Sixteen Personality Factor Questionnaire, Comrey's
Personality Inventory, Eysenck's Personality Inventory, and
an Adjective Checklist). Conclusions from the work in
Hawaii suggested fairly weak sibling resemblance on
personality variables.

For cognitive variables, intersibling correlations

typically range from .35 to .50 (Rowe & Plomin, 1981).

Reported correlations for monozygotic (MZ) and dizygotic
(DZ) twins on measures of ability are usually as high as
.82 and .52 respectively. In terms of personality
resemblance however, correlations are much lower for twin
and non-twin siblings. For example, in a study conducted
by Loehlin and Nichols (1976) correlations for M2 and D2
twins on three personality factors of the California
Psychological Inventory were, respectively, .50 and .30 on
sense of well being: .53 and .35 on tolerance; and .48 and
.30 on good impression. Similar correlations were found in
another study by Lykken, Tellegen, and DeRubeis (1978).
While these correlations are much higher than those for
personality measures, those for non-twin siblings were
weaker.

These data suggest that siblings who grow up in the
same home environment sharing the same parents and
community show little resemblance on personality variables.
This was especially true for non-twin siblings. The
observation that M2 twins were the most similar, followed
in turn by Dz twins and non-twin siblings, suggests that
genes may influence both cognitive and personality
development. This particular observation is a current
point of much contention in the literature. Some argue
that these differences are accounted for by environmental

factors while others argue that these differences are

primarily genetically mediated with environment playing a
secondary role. Before examining research supporting the
validity of such arguments, it seems necessary to discuss
factors that researchers seem to agree do not account for
the magnitude of personality dissimilarity between
siblings.

Several investigators have studied a variety of
factors that may be related to sibling dissimilarity on
personality factors. Constellation variables such as birth
order, age, and sex of the sibling have been studied and
offered as a partial explanation for such differences
(Jacobs & Moss, 1976; Hilton,l967; Lehman & Christensen,
1985: Abramevitich, Certer, Pelper, 8 Stanhepe, 1986). A
major assumption implicit in studying constellation
variables is the idea that differences in sibling
constellation leads to environmental differences. For
example, differences in age perhaps leads to differences in
parental treatment (i.e., parents being most strict on
older siblings compared to younger ones) or sex differences
leading to differential parental treatment (i.e., males
being socialized to be aggressive and females being
socialized towards passivity). These differences produce
different environments for siblings (Scarr 8
Grajek, 1982).

while there have been studies conducted to support the

importance of constellation variables (Jacob 8 Moss, 1976;
Lehman, Lehman, 8 Christensen, 1985) most researches
believe, however, that the amount of variance these factors
account for is so minute (less than 10%) that there must be
other factors which better explain intersibling personality
differences (Daniels 8 Plomin, 1985; Scarr 8 Grajek, 1982:
Hauser 8 Sewell, 1985; Daniels 8 Plomin, 1987: Plemin 8
Foch, 1981; Ernst 8 Angst (1983); Scarr, Webber, Weinberg,
& Wittig, 1981).

Scarr and Grajek (1982) propose a genotype-environment
(G--->E) correlation theory which incorporates
contributions from an individual's genetic make-up as well
as their environmental experiences-when examining
intersibling differences. They posit that the degree of
personality dissimilarity amount of difference will depend
upon genetic as well as environmental differences. Thus,
the model integrates aspects of nature and nurture in terms
of explaining such differences.

In addition to describing the basic propositions of
the model Scarr and Grajek also hypothesize the likely
process whereby such differences occur. Conceptually,
three kinds of G--->E correlations are proposed to explain
why environmental differences between siblings are likely
to occur:_(1) passive; (2) evocative; and (3) active.

Passive G--->E correlations are thought to occur as a

result of genetically related parents providing child-
rearing environments consistent with the child's genotype.
With the passive G--->E correlations the parent's genotype
is said to correlate with the child's genotype. Since
parents provide an environment that correlates with their
own genotype, the environment is also assumed to correlate
with the genotype of the child. Evecative G--->E

correlations suggest that the responses of children with

 

different genotypes are likely to evoke different responses
from those in his/her environment. These responses from
others help shape subsequent development and are also
likely to correlate positively with the individual's
genotype. Active G--->E correlations reflect an
individuals' tendency to seek out environments which he/she
finds compatible and stimulating. Each of these G—-->E
correlations are viewed in a developmental context with
passive G--->E being most predominant in infancy and
childhood, and active being most characteristic of late
adolescence and adulthood. Evecative effects are likely to
exist throughout development. The conceptual foundation of
the model, regardless of the type of correlation explained,
suggests that differences occur as a result of differences
in a person's genetic structure.

Other investigators have proposed that while genetics

may influence differences in personality between siblings,

a theory stressing the importance of non-shared aspects of
an individual's environment may be related to intersibling
variance in personality (Daniels, 8 Plomin, 1985; Daniels,
1986: Dunn 8 Kendrick, 1982). Rowe and Plemin (1981)
presented a theoretical framework for understanding sources
of intersibling personality differences as well as
cognitive differences. These researchers suggested that
the following are possible examples of non-shared
environmental factors which could be related to
intersibling differences: (1) accidental factors which are
experiences unique to the individual: (2) nature of
sibling interaction: (3) family structure: (4) differences
in parental treatment; and (5) differences in extra-
familial networks.

Rowe and Plomin (1981) also reviewed research
conducted in each of the above stated areas. They
indicated that while accidental factors (i.e., physical
illness, prenatal and postnatal trauma, separation) would
probably be very effective in explaining individual
differences, these same factors would be ineffective when
used to explain differences in the general population.
Research conducted on exploring the nature of the sibling
relations suggests that this may not be a major source of
non-shared environmental influence. Research in this area

suggested that siblings behaved mutually towards each other

rather than complementary (Abramovitch, Corter, 8 Lando,
1979: Lamb, 1978). Dunn (1983) however, conducted a study
examining the nature of sibling relations in early
childhood and found some evidence that siblings do behave
in complementary rather than mutual manners.

Research on family structure variables as sources of
non-shared environment have already been discussed in the
section on constellation variables. In terms of parental
treatment, Rowe and Plomin also conclude, contrary to
popular opinion, that parents actually treat their children
more alike than different. Other researchers however,
suggest that differential parental treatment does occur in
families (Hilton, 1967; Jacobs 8 Moss, 1976).. Daniels et
al (1985) found evidence that children reported being
treated differentially by parents who perceive themselves
as treating their children similarly.

The area of extra-familial networks proved to be one
of the more promising major sources of non-shared
environment. Rowe and Plomin reviewed research which
suggested that siblings contact with diverse peer groups,
extended family members, or teachers may be highly related
to intersibling dissimilarity on personality measures.

Not until recently have there been research efforts
directed at examining multiple factors and utilizing

instruments that specifically address the effects of non-

shared environment on personality dissimilarity (Daniels,
1986; Daniels 8 Plomin, 1985; Daniels, Dunn, Furstenberg, 8
Plomin, 1985). Conclusions about the significance of non-
shared environments in explaining intersibling personality
differences have been based on research with genetically
unrelated (adopted) siblings whose resemblances are
considered a direct estimate of shared sibling environment
since there is no genetic influence. Because adopted
siblings are also dissimilar on various personality
measures, this suggests that perhaps what is non-shared
rather than what is shared in siblings environment may
explain intersibling differences (Daniels, 1986).

While Scarr's genetic theory seems to offer an
interesting explanation of why siblings may differ, it is
based on assumptions difficult to assess. Scarr suggested
that parents provide environments which correlate with the
child's genotype. How does one measure the degree to which
one's environment is a result of one's genotype? While
this might be an interesting conception of how siblings
develop distinct personalities, its attractiveness is
somewhat diminished by the inability to assess genotypes
with current technology. On the other hand, Rowe and
Plomin's theory of non-shared environment lends itself to
direct empirical investigation. Not only can this concept

be measured through self-report inventories, it is

 

10

theoretically possible, albeit very difficult, to measure
non-shared environment through direct observations.
W

Consequently, the present study examines the
extent to which self-reports of one's non-shared
environment can predict and account for personality
dissimilarity between biological related sibling. It is r
hypothesized that non-shared environmental measures will

predict and account for most of the variance associated

 

with intersibling personality differences. It is also
predicted that age, sex, and birth order will account for
less than 10* of the total variance in terms of personality

differences.

£31392
All sibling pairs were required to complete a number

of self-report measures which assessed perceptions of
environmental experiences and personality styles.
University resident participants mailed out questionnaires
for their respective siblings to complete and return. A
detailed description of the sample, instruments, and
procedures are indicated below. f
Souls

The participants were 210 undergraduate students

attending a major midwestern University. All were enrolled

 

in an introductory psychology course and received extra
credits toward their course grade. The final sample
(after non-university resident siblings returned
questionnaires that had been mailed out) consisted of 111
sibling pairs, representing a 53% return rate. Of the 111
pairs, one was half-biologically related; 2 pair were
adoptive; and 8 pairs were spoiled due to non-university
resident participants incorrectly completing the
questionnaires or the age span between the siblings was
beyond four years. Thus, 11 pairs were excluded from data
analyses. Of the 100 remaining biological sibling pairs,
83 were of the same sex (37 brothers and 46 sisters) and 17
were not. Most pairs (62) were first-second born, 9 were
first-third born, 14 were second-third born, 10 were third-

forth born, and the remaining six were various combinations

11

12

(second-fifth, first-fourth, etc.). The university-
resident siblings ranged in age from 18 to 22: with an
average age of 19.28 years (SD- 1.08). Their siblings
partners ranged in age from 14 to 25 years; with a mean age
of 19.29 years (SD- 3.10). The average age for the entire
sample was 19.29 (SD - 1.80). In terms of parental
education, mothers averaged 14.33 years of education while
fathers averaged 15.21. Of the total sample 95% were E

Caucasian; 2% were African Americans; 2% were Asian

 

Americans: and 1% was Native American.
Instruments

The Sibling Inventory of Differential Experience
(SIDE) was used as a measure of non-shared environment
(Daniels 8 Plomin 1985, 1984: Daniels, 1986). This 73-item
inventory measures sibling interaction, parental treatment,
peer characteristics, and events specific to the individual
(the scale measuring events specific to the individual was
not used in this study). The following SIDE sub-scales
address 11 separate areas: (1) differential sibling
antagonism: (2) differential sibling jealousy: (3)
differential sibling caretaking; (4) differential sibling
closeness: (5) differential maternal affection: (6)
differential maternal control: (7) differential paternal
affection; (8) differential paternal control; (9)

differential peer college orientation; (10) differential

13

peer delinquency: (11) differential peer popularity. Based
on a sample of 57 biological sibling pairs from the Denver
metropolitan area, two-week test-retest reliabilities of
these sub-scales ranged from .77 to .93, with a mean of .84
(Daniels 8 Plomin, 1985). Their intercorrelations were
generally low to moderate and only 19 of 55 reached the .05
level of significance. Also the extent of sibling
agreement was low to moderate with a -.49 median

correlation value (the negative sign indicates agreement

 

between the two siblings on their perceptions of their
environment).

Personality in this study was operationally defined by
the five temperament scales of the Emotionality Activity
Sociability Temperament Inventory (EAS) (Buss 8 Plomin,
1984). According to Buss and Plomin, aspects of
temperament assessed on this measure show the greatest
amount of stability over time in terms of personality
development. It is assumed by some, but not yet proven,
that aspects of emotionality, activity, and sociability
exist at birth and may be of genetic origin. The five
temperaments assessed by the EAS include emotionality-
anger, emotionality-fear, emotionality-distress, activity,
and sociability. Two-week test-retest reliabilities were
obtained from 34 university undergraduates yielding

stability coefficients ranging from .75 to .85. The EAS

14

also had an overall test-retest reliability of .82.
Intercorrelations among EAS scales were low to moderate
with the largest significant correlation occurring between
distress-anger and activity (2 -.57). The other
temperament measures were fairly independent in their
structure (Buss and Plomin, 1984).

Although many problems have been identified when
relying upon self-report data, this was judged the most
appropriate form of data collection because perceptions of
the participants are central to understanding how they
interpret their environment. Nevertheless, the Marlowe-
Crowne Social Desirability Scale was also administered as a
control measure for positive response bias. A comparison
of those participants who responded in a socially
acceptable manner versus those who did not will be
undertaken in the statistical analyses section. A Personal
Data sheet was also completed by each participant to
compile appropriate demographical information (see Appendix
A, p. 33).

PM

There were four separate group administrations which
consisted of approximately 50 participants at each session.
Packets of questionnaires were placed on each desk face
down when the participants arrived at the testing location.

Each packet contained the following data:

 

15

1. Statement of Informed Consent

2. Personal Data Sheet

3. Sibling Inventory of Differential Experience

4. Emotionality Activity Sociability Inventory

5. Marlowe-Crowne Scale

6. Debriefing Letter

7. Form Letter

8. Envelopes

9. Sibling Packet with same information

' After all participants arrived at the research

location, the examiner introduced herself and the research
project. All participants were told that the project was
being conducted to examine how sibling relationships
related to personality development. Participants were then
instructed to read and sign the Statement of Informed
Consent (see Appendix B, p. 35). After all participants
had completed the consent form, the examiner provided
necessary instructions to complete the Personal Data Sheet
. and the necessary SIDE information.

Once the preliminary information had been completed,
they were told they could begin completing the
questionnaires and to stop at any point and ask questions
if they were unsure about the instructions. For those
participants with more than one sibling within four years

of age, a die was used to randomly determine who they were

 

16

to compare their responses to on the SIDE questionnaire.
Once participants began to complete the questionnaires, the
group was then given instructions on how to complete the
letter that was to accompany the packet being mailed to
their sister or brother (see Appendices C 8 D, pp. 38-41
for forms used in packets). They were also given !
instructions on how to fill out the envelopes in which the
packets were being mailed. A debriefing note (see Appendix

E, p. 43) was provided for each of the participants.

 

After completing all necessary information participants'
packets were checked to make sure they had been filled out
correctly and they were then permitted to leave. This
procedure was followed for each of the subsequent data

collection sessions.

BBEQLIE
The first part of the data analyses involved providing

descriptive statistics on the various measures while
subsequent analyses involved examining how constellation
variables and non-shared environment related to personality
differences. Means and standard deviations for the
Emotionality Activity Sociability Inventory (EAS) are
listed below in Table 1. The present means are very
similar to those in Buss and Plomin's (1984) normative
sample shown in Table 1. The only statistically
significant intersibling difference was university
residents' higher sociability ratings.

Table 1
Eeans_and_Standard_nexiations_for;EA§
Xariables Siblins_b, Sibling_fi Normatixe_uean§
MEAD §D Mean ED Males females
Sociability 3.85‘ :70 3.49 .80 3.81 3.25
Activity 3.53 .68 3.37 .75 3.35 3.20
Fear 2.62 .59 2.59 .79 2.65 2.23

Emotionality 2.39 .76 2.37 .82 2.52 2.43

Anger 2.91 .80 2.95 .86 2.57 2.70

 

Note; Sibling A - University Resident Sibling and

Sibling B a Non-University Resident Sibling. Values ranged
from 1 to 5 on the EAS with 1 being least typical of the
respondent and 5 being most typical of the respondent.

*p < .001.

17

 

18

When separating pairs according to sex (M-M, F-F),
male pairs where found to describe themselves as
significantly (p < .05) less fearful and emotional than
female pairs.

Means and standard deviations for the Sibling

- .‘ 'Afl

Inventory of Differential Experience (SIDE) were based on
the relative scoring system with the following values:
1.00 - my sibling has been much more this way than I have:

2.00 - my sibling has been a bit more this way than I have:

 

3.00 - my sibling and I have been the same in this way:
4.00 - I have been a bit more this way than my sibling; and
5.00 - I have been much more this way than my sibling. The
present means (see Table 2) are very similar to those
obtained in the normative sample and other research
(Daniels, 1986: Plomin 8 Daniels, 1985). The magnitude of
the present standard deviations suggest that siblings
perceived aspects of their environment as being dissimilar.
For example, the mean for differential sibling caretaking
was 3.21 for sibling A with a standard deviation of .70.
This mean implies that on the average sibling A believed
that he/she differed little from sibling B on this
variable. However, the variance (SD - .70) suggests that
some group A siblings viewed themselves as being more of a
caretaker while there were others who viewed group B

siblings as being more of a caretaker.

19

Table 2
W
W slum

Mean SD Mean SD
Sibling Caretaking 3.21 .70 2.93 .71
Sibling Antagonism 2.91 .48 2.94 .55
Sibling Jealousy 2.86 .78 3.36 .70
Sibling Closeness 2.86 .65 3.08 .63
Paternal Affection 3.09 .54 2.96 .53
Maternal Control 3.05 .69 3.15 .68
Maternal Affection 3.05 .62 2.77 .57
Paternal Control 3.04 .62 3.05 .59
Peer College Orient. 3.42 .63 2.99 .59
Peer Delinquency 3.33 .67 2.89 .67
Peer Popularity 3.02 .66 3.03 .76

.28
-.05
-.61
-.21

.11
-.11

.29
-.02

.43

.44

-.03

5.1211811 MILD

.05

.00

.05

 

.008

.00

.001

 

Note; sibling A - University Resident Sibling and Sibling
B - Non-University Sibling. Orient. - Orientation.

Responses on the Marlowe-Crowne Scale of Social

Desirability Scale were correlated with the responses on

the EAS and SIDE scales.

These correlations were generally

weak (maximum I - .25) and so few of them (5 of 32) reached

significance that further analyses seemed inappropriate

(see Tables 3 8 4, Appendix F, pp. 45). The lack of

significant correlations between the Marlowe-Crowne with

20

the EAS and SIDE scales suggests the responses of
participants were not likely to be related to attempts to
respond to items in a socially desirable manner.

Since the primary purpose of the study involved
predicting intersibling personality differences from the.
SIDE scales, single personality difference scores were
created for each sibling pair. These scores were computed

by subtracting the score of sibling B from that of sibling

 

A separately for each EAS scale. To obtain single scores
for sibling pairs on the SIDE scales their scores were
averaged since sibling agreement on the SIDE measure ranged
from -.23 to -.73. These negative signs indicate that
siblings agree on the perceptions of their experiences
measured by the SIDE (Daniels 8 Plomin, 1985).

Means and standard deviations for personality
differences scores are listed in Table 5. None of the
differences between sibling pairs were statistically
significant. In addition, when scores were separated by
sex of pair (M-M, F-F), there were no statistically
significant differences. Means and standard deviations for
the average sibling score on the SIDE scales are listed in
Table 6. Even when averaged, most of the scores center
around 3.00. When the sample was separated into female and
male pairs, sisters viewed their mothers as differing

significantly in the degree of affection given,

21

 

 

but brothers reported no parallel differences. No other
significant gender-pair differences where found.
Table 5

WW
5221:: HEAD SD
Sociability .36 1.03
Activity .16 .94
Fear .03 1.02
Emotionality .02 1.06
Anger -.03 1.13

Table 6

W

W

SIDE_§£§12§ Mean 52
Sibling Jealousy 3.10 .38
Sibling Caretaking 3.07 .29
Sibling Closeness 2.96 .38
Sibling Antagonism 2.93 .29
Paternal Control 3.06 .34
Maternal Control 3.10 .37
Paternal Affection 2.94 .43
Maternal Affection 2.90 .30
Peer College Orientation 3.22 .29
Peer Popularity 3.11 .32
Peer Delinquency 3.00 .35

 

22

Correlations for sibling personality resemblance on
the EAS measures are listed in Table 7. These findings
suggest rather modest intersibling resemblance. In terms
of magnitude, these correlations were much like those found
in other studies examining sibling resemblance. There
were, however, a few statistically significant differences
when correlations were separated according to sex of pair,
sisters significantly resembled each other in activity
level and opposite-sexed pairs significantly resembled each

 

other in terms of emotionality.

 

Table 7
EAS_C9rrelati9n§_netxeen_§iblins_£airs
(N530, iii‘if’éi ”iii???“ iii—iii?
Sociability .05 .07 .05 .30
Activity .11 .30“’ -.12 -.08
Fear .04 -.04 .07 .21
Emotionality .11 -.09 .17 .41'
Anger .09 .08 .17 .09
*p < .05.
**p < .01.
~-.. ;- ‘u! .. - 2 .. - . -. v. .. -~

Table 8 lists the correlations for EAS measures with

constellation variables. The significant correlations

23
suggest that from 1% to 38% of the variance in personality
difference scores may be accounted for by constellation
variables (Ozer, 1985). In terms of gender, females
described themselves as significantly more fearful and
sociable than males. Older siblings were likely to report
being more emotional than younger siblings. Finally, F
later-born siblings reported being more fearful than !

earlier-born siblings.

Table 8

 

-01. D ‘ ‘I : o -‘ .go o! c . o. . .0

gender Ase Dimmer.

 

Sociability - . 25'm - . 02 . 03
Activity .02 -.13 .09
Fear . 37... . 14 . 19'
Emotionality -.13 .17. .09
Anger . 07 . 04 . 06
*p < .05.

**p < .005.

***p < .000.

Tables 9, 10, and 11 present correlations between
personality difference scores and SIDE scores according to
sibling interactions, parental treatment, and peer group

characteristics respectively.

24

Table 9
W

mm 11931933.! Closeness
(n - 89) (n - 97) (n - 85) (n = 97)

I ’ :9“?

 

Sociability . 20' -. 16" . 16 -. 06
Activity .09 -.12 -.07 -.10
Emotionality .12 -.04 .04 -.05
Fear .02 .12 .02 -.11
Anger . 12 . 01 . 17 -. 10
*n < .05.

Table 10

MLQQDLIQI ELAIIQQLIQD
(n = 95) (n = 93) (n - 90) (n = 84)
Sociability .04 -.15 ‘ .07 -.14
Activity .03 .03 .02 -.09
Emotionality .13 .14 -.02 .15
Fear .00 .11 -.08 .08
Anger . 02 . 04 . 19' - . 12

 

Note; M = Maternal and P - Paternal.
*n < .05.

25

Table 11
. - , . ,. __ . . , -
(n " 95) W (n ' 89)
Sociability -.02 -.07 .01
Activity -.01 -.00 -.05
Emotionality -.02 .09 -.03
Fear .18' .00 - .04
Anger .19' .14 -.03

 

Ngtgy Ort. a Orientation, Delinq. - Delinquency.
*p<.05.

Most of the 55 correlations in tables 9, 10, and 11
were weak and non-significant. Of these, five significant
correlations across areas accounted for only 1% to 20% of
the variance in the personality difference scores (Ozer,
1985). In the absence of any substantial statistically
significant correlations, multiple regression analyses

seemed inappropriate.

DIEQHEEIQE_A£D_QQEQLHEIQEE

As was indicated in the results section, the means and
standard deviations for each of the measures utilized in
this study were consistent with both normative samples and
prior samples (Daniels, 1986: Buss 8 Plomin, 1984: Daniels
8 Plomin, 1985). Theses data indicate that the present
sample did not differ appreciably from that of prior
studies.

Results relevant to personality resemblance indicated
that these siblings tended to describe themselves as more
similar than dissimilar even though the relationships were
generally weak and statistically non-significant. In
magnitude these intersibling correlations resembled those
presently reported in the literature (Daniels 8 Plomin,
1987: Scarr 8 Grajek, 1982: Dixon 8 Johnson, 1980). Thus,
the findings in this study are consistent with other
research examining sibling resemblance. The specific
finding that females described themselves as more fearful
and sociable than males was also previously reported
(Daniels, 1986). Gender related differences between males
and females on variables that have been traditionally
associated with one sex versus the other were not
surprising given this society's differences in the
socialization of males and females.

It was hypothesized that constellation variables would

account for 1% to 10% of the variance in personality

26

27

difference scores. The present findings did not support
this hypothesis. This result was inconsistent with
findings by other researchers who suggested that these
variables explain very little of the variance associated
with intersibling dissimilarity. Results indicated that
gender, age, and birthorder combined accounted for 1% to
38% of the variance in personality difference scores.

This difference in variance estimates is apparently an
artifact of statistical methodology used to derive such
estimates. It appears that Daniels (1986) used squared
correlations to estimate the variance accounted for in her
study. The present study employed estimates representing
the actual size of the Pearson correlations. This method
was preferred based on an article by Ozer (1985) which
suggested that using the squared correlations as estimates
of variance could underestimate the amount of variance in
research were the actual correlation coefficient might
better explain the significance of the relationship between
the variables.

It had been predicted that the SIDE measure would
account for much more of the variance in personality
difference scores than would the constellation variables.
This hypothesis was also rejected. Most of the present
correlations between the SIDE scales and personality

difference scores were weak and nonsignificant. This

28

finding suggests that the non-shared environment factors
examined in this study were largely unrelated to
intersibling personality differences. This finding is also
inconsistent with other research in this area.

A number of explanations may account for non-shared
environmental factors being poor predictors of intersibling
personality dissimilarity. Since the SIDE instrument was
developed for junior and senior high school students, it is
possible that it was not fully appropriate for this sample.
However, SIDE's developers indicated that it could be used
with older siblings as long as respondents were instructed
to base their responses on a certain time period when they
were living at home. Although this procedure was adhered
to in this study, perhaps being physically removed from the
home environment may have made it difficult for
participants to accurately recall various aspects of their
home experiences. Although this explanation lacks direct
support, it seems compatible with correlations between
siblings' SIDE responses. Intersibling correlations were
generally low to moderate (-.07 to -.56), indicating weak
to moderate agreement.

It is also possible that there may be events which
occur specific to the individual that could better explain
the obtained degree of intersibling similarity observed.

Similar events which occur in the same home environment and

29

community may impact one sibling differently than another
and mediate differences in personality development. Thus,
future research in this area should utilize instruments
that more closely examine the extent to which experiences
unique to the individual that may be related to personality
development. The exploration of such factors does not
imply that the SIDE inadequately assesses non-shared
environmental factors: perhaps both types of variables play
a significant role in understanding intersibling
personality dissimilarity.

Just as instruments assessing environmental influences
on personality development need refining, the manner in
which personality was conceptualized and assessed in the
present study may also be in need of refinement. The EAS
Inventory was used to operationalize the concept of
personality in this study because these variables were
thought to be present as early as infancy and remain
relatively stable throughout development. Perhaps
personality style does not remain stable, but changes with
experiences and subsequent development. Future research
examining a wider ranger of variables may help clarify the
nature of personality development beyond infancy and
childhood.

In conclusion, even though the constellation variables

were more strongly related to personality difference scores

30

than was SIDE, this does not imply that these are the only
variables that account for variation in personality
dissimilarity. Since genetic contribution was not
controlled in this study, it cannot be concluded that these
findings were not mediated by genetic influence. Despite
the fact that causation cannot be inferred from these data,
the significant relationships that were obtained with
constellation variables suggest that the latter variables
may be more important than previously assumed. While the
current investigator is unlikely to further explore this
area beyond this study, those interested in future research
might do well to explore theories which provide a more
integrative approach with the expectation that such
theories might provide a better understanding of
intersibling personality development.

APPENDICES

APPENDIX A
W

APPENDIX A

 

 

 

 

W
Name:
Address:
City: State:
Zip Code:
Date of Birth: Sex:

 

 

 

Ethnic/Racial Background:

Your Birth Order in family (i.e. Ist born, 2nd born,
etc.):

 

Is your sibling:

 

Biological related: yes no
Adopted: yes no
Half: yes no
Step: yes no
Foster: yes no

Number of additional siblings:

Please indicate the highest grade or degree completed for
each parent:

Mother:

 

Father:

 

33

APPENDIX 8
WW

APPENDIX 8
W

I understand that:

Subject Signature

Date

I.

II.

III.

IV.

If at any point I begin to feel uncomfortable
about participating, I can discontinue my
participation.

The study that I am participating in is designed
to explore the nature of sibling interaction and
personality styles.

The study requires me to attend one lab sessions
where I will complete three questionnaires and
personal data inventory. My responses to the
questions will be treated confidential and I
will remain anonymous as results are discussed.
I may also obtain information regarding the
results of my participation, if requested.

My sibling will be mailed the same
questionnaires to be completed. My credit for
participation, however, will not be based on
whether or not my sibling returns the
questionnaires.

I am not to discuss the manner in which I
responded to the questions with my sibling or

other students.

35

”Du rsv'zqnnnon F "

APPENDIX e
W

 

APPENDIX C
W.

Dear :

As a part of a project I am participating in at MSU,
I need you to complete and return the enclosed
questionnaires as soon as possible. I have already
completed a copy of the questionnaires, but my responses
cannot be evaluated unless you also complete the
questionnaires. There is a statement of informed consent
you must read and sign. If there are any questions you do
not understand, please leave them blank. You should
complete the questionnaires without assistance from anyone.
After they are complete, please mail them back in the self-
addressed stamped envelope as soon as possible.

Thanks!!!!!
(Form Letter for Minors)

Dear :

As a part of a project I am participating in at MSU,
I need you to finish and mail back the enclosed
questionnaires. I have already finished a copy of the
questionnaires, but my answers can not be checked unless
you also complete the questionnaires. There is a
permission statement enclosed that you and mom or dad must
read and sign before completing the questionnaires. If

there are any questions you do not understand, please leave

37

 

38

them blank. You should complete them without help from
anyone. After they are complete, please mail them back in

the self-addressed stamped envelope as soon as possible.

APPENDIX D

Wages;

APPENDIX D

Want

I understand that:

I.

II.

III.

IV.

VI.

VII.

Participant's Signature

Date

If at any point I begin to feel uncomfortable
about participating in the study, I can
discontinue my participation.

If I am under the age of 18 I must have one of
my parents sign this consent form.

The study in which I am participating in is

 

designed to elicit information about sibling
interaction and personality styles.

This study requires me to complete three
questionnaires and one personal data inventory.
These questionnaires should be completed without
soliciting help from my sibling who has also
completed the questionnaires or my parents. Any
questions that are not understood should be left
blank.

That my participation is voluntary and no
penalty will be imposed upon my sibling if I
choose not to participate.

Results of the study can be obtained if

requested.

Parent's Signature (if a minor)

 

4O

APPENDIX E
W

 

APPENDIX E
W

The study in which you have participated was
designed to better understand factors associated with
personality dissimilarity between siblings. Currently,
most of the research indicates that siblings from the same
family tend to develop very dissimilar personality styles.
Some argue that this is basically due to genetic factors,
while others argue that dissimilarity is due to
environmental factors. Undoubtedly, both factors influence
personality development, however: it would be very
beneficial to research on personality development to
determine which of the two factors have the greatest impact

on development.

42

APPENDIX F

APPENDIX F

-- ,- ._ » --
' r. .A '..' '. i '__ '

Table 3
EAS_Inxent9rX_8_EaIlorezsroune_sorrelations
Ysriables Siblins_8. .Siblins_n
Sociability .09 .02
Activity -.05 -.02
Fear -.02 -.25"
Emotionality -.01 -.23'
Anger .11 -.08

 

Note; Sibling A a University resident sibling and Sibling
B - non-University resident sibling.

gun-luv

 

*p < .01.
up < .005.
Table 4
W
W 51.121.189.15 W
Sibling Antagonism .12 -.08
Sibling Caretaking -.04 .02
Sibling Jealousy .01 -.05
Sibling Closeness -.05 .01
Maternal Affection -.22" -.12.
Maternal Control .08. .19
Paternal Affection .17 .14
Paternal Control .01 .13
Peer College Orientation -.11 -.03
Peer Delinquency .21 .09
Peer Popularity .11 .03

Hose. *2 < .05.

*R < .01.

44

 

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