Handbook of Psychopathy Chapter 11 Notes: Genetic and Environment on Psychopathy and AB

Chapter 11 Genetic and Environment on Psychopathy and AB

Behavior genetic designs have the advantage of disentangling genetic
and environmental influences, the effects of nature and nurture, and
characterizing the relative magnitudes as an important step in
explaining etiology, to be followed by the search for specific
candidate genes and environmental risk factors. Although is not
possible to disentangle genetic from environmental factors in family
studies because these are confounded in nuclear families, twin and
adoption studies have the unique ability to disentangle genetic and
environmental influences and to estimate the magnitude of both
simultaneously.
p. 205

Confounding among Moderators: 1 of 2
AB is operationalized and assessed differently for children,
adolescents and adults (e.g., CD assessed via parent report in
children versus APD assessed via self-report in adults). Also,
certain operationalizations of AB are most frequently or readily
assessed using certain records (e.g., criminality via official
records). Therefore, age of participants, operizationalization, and
assessment method may be highly correlated across studies of AB. Such
confounding of moderators can make the interpretation of results in
2-ways: 1) if 2-confounded moderators are both found to be
significant, it is possible that the 2nd moderator is significant only
because it correlates with the first. Fortunately, this problem can
be assessed in the present meta-analysis by testing the significance
of a particular moderator after other moderators are controlled for
statistically.
p. 209.

Confounding among Moderators: 2 of 2
2) If one level of a moderator is completely confounded with a level
of another moderator (e.g., all studies examining criminality being
assessed by records) it is possible to determine whether the results
reflect the first or second moderator. It can be addressed in future
research by diversifying the pairings among operationalization,
assessment methods, and age (e.g., more more studies of criminality
using a variety of assessment methods, rather than official records
alone).
p. 209.

Hard to draw conclusions from twin-adoption studies
Although more than 100 twin and adoption studies of AB behavior have
been published, it is difficult to draw clear conclusions regarding
the magnitude of genetic and environmental influences on antisocial
behavior given the current literature. The main reason for this
difficulty is the considerable heterogeneity of the results in this
area of research, which public estimates of heritability (i.e., the
magnitude of genetic influences) ranging from very low (e.g., .00;
Plomin, Foch & Rowe, 1981) to very high (e.g., .71; Slutske et al.,
1997). Various hypotheses have been proposed to explain this
heterogeneity in results across studies, including differences in the
age of the sample (e.g., Cloninger & Gottesman, 1987), the age of
onset of AB (e.g., Moffitt, 1993), and the measurement of antisocial
behavior (e.g., Plomin, Nitz & Rowe, 1990).
p. 205.

meta-analysis of 51 twins & adoption studies
Conducted a meta-analysis of 51 twins & adoption studies in order to
provide a clearer and more comprehensive picture of the magnitude of
genetic and environmental influences on AB, and to test several
alternative hypotheses regarding moderating variables that may explain
the heterogeneity in the magnitude of these influences on AB. p. 206

meta-analysis: behavior genetic studies of psychopathy I
In addition to the main meta-analysis of behavior genetic studies of
AB, and the tests of the various moderators of the various moderators
of the considerable heterogeneity in the genetic and environmental
influences therein, also conducted was a follow-up meta-analysis of
data from studies of psychopathy alone. Additive genetic influences
accounted for 49% of the variance and nonshared environmental
influences accounted for the remaining 51% of the variance in
self-report of psychopathy. Additive genetic influences were clearly
more important than shared environmental influences in explaining the
familiality of psychopathy. A twin study (Taylor et al., 2000) that
used self-reports on the California Psychological Inventory (CPI)
Socialization scale to assess psychopathy yielded identical results.
p. 218.

meta-analysis: behavior genetic studies of psychopathy II
Taylor and colleagues (2003) estimated genetic and environmental
influences on 2-subscales (antisocial & detachment) of the Minnesota
Temperament Inventory (MTI) in 2-cohorts, ages 16-18, from the
Minnesota Twin Family Study. The MTI is a 19-item self-report measure
designed to assess the classical features of psychopathy as described
by Cleckley (1941). There was no evidence for shared environmental
influences on either of the scales. Additive genetic influences
accounted for 53% and nonshared environmental influences accounted for
the remaining 47% of the covariation between the two
psychopathy-related traits (AB and detachment). About 53% of the
genetic influences and 79% of the nonshared environmental influences
on Detachment were shared in common with those that also influence AB.
This indicates that whereas the vast majority of the nonshared
environmental influences on Detachment are the same as those on AB,
just over half of the genetic influences on Detachment are the same as
those on AB, suggesting that many of the genetic influences are unique
to each psychopathy trait.
p. 218-219.

meta-analysis: behavior genetic studies of psychopathy III
A twin study (Blonigen et al., 2003) used an adult male sample from
Minnesota to estimate genetic and environmental influences on the
total score and 8 subscales from the Psychopathic Personality
Inventory (PPI; Lilienfeld & Andrews, 1996; Lilienfeld & fowler,
Chapter 6: The Self-Assessment of Psychopathy: Problems, Pitfalls, and
Promises, this volume). (See: PPI article for subscales) The genitive
appeared to be nonadditive for all of the subscales except Social
Potency and Blame Externalization, for which the genitive influences
were additive. Genetic influences accounted for 29-56% of the variance
in each of the PPI subscales.
p. 219.

moderating effects on twin and adoptive studies
Moderating effects of 3-study characteristics: 1) the
operationalization of AB; 2) assessment method; and 3) and zygosity
(the condition relating to conjugation, or to the zygote, as (1) the
state of a cell or individual in regard to the alleles determining a
specific character, whether identical (homozygosity) or different
(heterozygosity); or (2) in the case of twins, whether developing from
one zygote (monozygosity) or two (dizygosity).Saunders Comprehensive
Veterinary Dictionary, 3 ed. © 2007 Elsevier, Inc) determination
method; and 2 participant characteristics: the age and sex of the
participants, on the magnitude of genetic and environmental
influences on AB. Examining these moderators effects will improve our
understanding of the characteristics will improve our understanding
of the etiology of AB. Examining these characteristics and moderators
has the potential to clarify issues regarding the degree of
heterogeneity in the etiology of AB (i.e., examination of the
operationalization of AB, age of the participants, and sex of the
participants), the development of AB (i.e., the examination of the age
of the participants), and the effects of potential methodological
confouders (i.e., examination of the assessment method and zygosity
determination method) on the results.
p. 206.

Operationalizaton of AB has 4 catagories – hypothesis 3 B Zygosity
Determination Method as a Moderator
Although all zygosity determination methods used in behavior genetic
studies of antisocial behavior have been shown to be valid, the
estimates of the magnitude of genetic and environmental influences may
be affected by the zygosity determination method. McCartney and
colleagues (1990) predicted that studies that used blood grouping
would have higher effect sizes for MZ twins and lower effect sizes for
DZ twins because the use of blood grouping in zygosity determination
would purify the MZ and DZ samples. They found that studies using
blood grouping did have higher effect sizes for MZ twins, but the
zygosity determination method did jnot moderate effect sizes for DZ
twins.
p. 208.

Operationalizaton of AB has 3 categories – hypothesis 1
Operationalization as a Moderator
Operationalizaton of AB has 3 categories (Plomin et al., 1990). 1) AB
has been examined in terms of psychiatric diagnoses, such as
antisocial personality disorder (APD) and conduct disorder (CD). 2)
AB has been operationalizationed in terms of the violation of legal or
social norms (i.e., as criminality and delinquency). 3) AB has been
operationalized as aggressive behavior. Also, several researchers
have examined an omnibus operationalization that includes both
aggression and delinquency items, such as the externalizing scale from
the Child Behavior Checklist (Achenbach & Eddelbrock, 1983). We
tested whether the magnitude of genetic and environmental influences
on AB varies with the operationalization of AB.
p. 206
hypothesis 2 A Assessment
Method as a Moderator
AB has been assessed via self-report, report by others (i.e., parent or teacher
report), objective measures (i.e., aggression toward a Bobo doll
Plomin et al., 1981), official records of criminality, and reactions
to aggressive material (e.g., whether or not one finds aggressive
humor to be funny; Wilson, Rust & Kasiel, 1977).
p. 206

Operationalizaton of AB has 4 categories – hypothesis 2 B Assessment
Method as a Moderator
Several studies have shown that assessment method can influence the
results of behavior genetic studies. McCartney, Harris & Bernieri
(1990) compared parent self-reports of sociability and found that
parent reports resulted in higher correlations than self-reports in
monozygotic (MZ) twins but resulted in lower correlations than
self-reports in dizygotic (DZ) twins. They also found that for
activity-impulsivity, parent reports resulted in higher correlations
than self-reports in both MZ and DZ twins. In contrast, Miles and
Carey (1997) found that behavior genetic studies of aggression using
parent reports resulted in lower heritability estimate when compared
to using self-reports.
p. 207-208

Operationalizaton of AB has 4 categories – hypothesis 2 C Assessment
Method as a Moderator
Researchers using temperament have found that parent reports tend to
yield DZ correlations that are very low or even negative. This may be
the result of parents exaggerating the differences between their DZ
twins, which as been described as a rater contrast effect (Loehlin,
1992a). One example of such findings emerged from the MacArthur
Longitudinal Twin Study (Emede et al., 1992). No resemblance of DZ
twins on measures of behavioral inhibition and shyness was found using
parent reports, but significant DZ resemblance was found using
observational measures of the same constructs.
p. 208

hypothesis 2 D Assessment
Method as a Moderator
Plomin’s (1981) review of twin studies examining personality concluded
that objectivity assessed behavior yielded lower heritabilities than
self-reports and parent reports. Similarly, Miles and Carey’s (1997)
meta-analysis of behavior genetic studies of aggression concluded that
2-studies using an objective method found little evidence of genetic
influences on aggression, in contrast to studies using self-report or
parent report. We thus tested whether assessment method is a
moderator of the magnitude of genetic and environmental influences on
AB.
p. 208

hypothesis 3 A Zygosity Determination Method as a Moderator
Also tested was whether zygosity determination method is a moderator
of genetic and environmental influence on individual differences in
AB. Zygosity determination methods used in twin studies of AB
behavior include blood grouping and questionnaires, and a combination
of the two methods. The inaccuracy of blood grouping in determining
the zygosity of twin pairs is less than 1% (e.g., Smith & Penrose,
1955). Questionnaire methods of determining zygosity, which involve
asking about the physical similarity of the twin pairs, have been
found to agree highly with zygosity diagnosis by blood groupings and
DNA markers. Kasriel and Eaves (1976) found that if all twin pairs
who agree that they were confused in childhood and are alike in
appearance are determined to be MZ, only 3.9% of the simple would be
diagnosed incorrectly, while Rieveld and colleagues (2000) found that
agreement between zygosity determined questionnaire method and
zygosity determined by DNA markers and blood typing was around 93%.
p. 208

hypothesis 4 A Age as Moderator
Age as a moderator, comparing results for children (below age 13),
adolescents (13-18), and adults (above age 18). Age was tested as a
moderator of the magnitude of genetic and environment influences on AB
for 2-reasons: 1) in the behavior genetics literature, there is a
general finding for a variety of traits that as age increases, the
magnitude of genetic and nonshared environmental influences increases,
whereas the magnitude of shared environmental influences decreases
(Lochlin, 1992a; Plomin, 1986). One example of such a finding is
Matheny’s (1989) longitudinal study of temperament. Over 12 to 30
months of age, MZ twins become more concordant than DZ twins for
age-to-age changes in temperament measures of emotional tone,
fearlessness, and approach. In Miles and Carey’s (1997) meta-analysis
of behavior genetic studies examining aggression, the magnitude of
shared environmental influences decreased and the magnitude of genetic
influences increased from childhood to adulthood.
For Reason 2 see: Operationalizaton of AB has 4 categories –
hypothesis 4 B Age as Moderator
P. 208-209.

hypothesis 4 B Age as Moderator
For Reason 1 see: Operationalizaton of AB has 4 categories –
hypothesis 4 A Age as Moderator
Reason 2) Age was examined because of the potential to test an
interesting alternative hypothesis regarding the development of AB.
DiLalla and Gottesman (1989) and Moffitt (1993) have suggested that AB
individuals can be divided into a smaller group whose AB is persistent
throughout the life course and influenced predominantly by genetic
influences; and a larger group whose AB is limited to adolescence and
influenced primarily by environmental influences. If their hypothesis
is correct, the relative magnitude of genetic influences on AB should
be lower in adolescence than in childhood than in childhood or
adulthood.
p. 209.

hypothesis 5 Sex as Moderator
No matter how AB is operationalized or assessed, it is more prevalent
in males than females (e.g., Hyde, 1984; Wilson & Hernstein, 1985).
Given this sex difference is prevalent, it is important to consider
whether the magnitude of genetic and environmental influences differs
in males in males and females. Past literature reviews (e.g., Widom &
Ames, 1988) have suggested that the magnitude of genetic and
environmental influences on AB is equal for the 2-sexes, whereas Miles
and Carey (1997) found that the magnitude of genetic influences on
aggression was slightly higher for males than for females.
p. 209.

PPI: Psychopathic Personality Inventory
The PPI subscales include: Machiavelian Egocengtricity, Social
Potency, Fearlessness, Coldheartedness, Impussive Nonconformity, Blame
Externalization, Carefree Nonplanfulness and Stress Immunity.
p. 219.

summary on meta-analysis & recent behavior genetic studies of
psychopathy
A meta-analysis of behavior twin studies suggested that genetic
influences on psychopathic traits are appreciable and may be
nonadditive, with moderate nonshared environmental influences but no
evidence for shared environmental influences across studies (in
contrast to the meta-analysis results for the aforementioned behavior
genetic studies of AB). These studies raise the possibility that some
of the genetic influences on development of AB may be mediated via
psychopathic personality traits (e.g., Taylor et al., 2003), and raise
the question as to what extent the heritability of psychopathic traits
is coextensive with genetic influences on “normal range” personality
traits such as negative and positive emotionality, and daring or
constraint (Benning, Patrick, Blonigen, Hicks & Iacono, 2005; Lahey &
Waldman, 2003).
p. 219.

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