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Association Between Self-reported Childhood Sexual Abuse and Adverse Psychosocial Outcomes
Results From a Twin Study
Elliot C. Nelson, MD;
Andrew C. Heath, DPhil;
Pamela A. F. Madden, PhD;
M. Lynne Cooper, PhD;
Stephen H. Dinwiddie, MD;
Kathleen K. Bucholz, PhD;
Anne Glowinski, MD;
Tara McLaughlin, PhD;
Michael P. Dunne, PhD;
Dixie J. Statham, MCP;
Nicholas G. Martin, PhD
Arch Gen Psychiatry. 2002;59:139-145.
ABSTRACT
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Background Increased risk for serious adverse outcomes has been associated with
a history of childhood sexual abuse (CSA). Whether these risks are directly
attributable to CSA rather than family background remains controversial.
Methods Structured psychiatric telephone interviews were conducted from February
1996 to September 2000 with both members of 1991 same-sex pairs (1159 female
and 832 male pairs) from a young adult Australian volunteer twin panel (mean
[SD] age, 29.9 [2.5] years). A binary composite CSA variable was constructed
from responses to 5 component questions. The association between CSA and adverse
psychosocial outcomes was examined, controlling for family background.
Results A history of CSA, reported by 16.7% of the women and 5.4% of the men,
was more common among those reporting parental alcohol-related problems. Significantly
increased risk was observed in women reporting a history of CSA for subsequently
occurring major depression, suicide attempt, conduct disorder, alcohol dependence,
nicotine dependence, social anxiety, rape after the age of 18 years, and divorce;
most similar risks reached statistical significance in men. The greatest risks
were associated with CSA involving intercourse. Childhood sexual abuse–negative
twins (ie, those who denied having experienced CSA) from CSA-discordant pairs
compared with other CSA-negative individuals had increased risk for many adverse
outcomes suggesting correlated family background risk factors. Childhood sexual
abuse–positive members (ie, those who reported having experienced CSA)
of CSA-discordant pairs had significantly greater risk for all 8 examined
adverse outcomes than their co-twins.
Conclusions Self-reported CSA was associated with increased risk for adverse outcomes,
controlling for family background. Family background risk factors also were
associated with adverse outcome risk. Discordant pair analysis seems to provide
an effective means of controlling for family background risk factors.
INTRODUCTION
INCREASED RISK for serious negative outcomes has been reported for individuals
with a history of childhood sexual abuse (CSA).1-3
However, 2 major methodological issues, ascertainment or selection bias and
confounding aspects of the family environment (eg, parental alcoholism), complicate
interpretation of reported associations. Many investigations have relied on
samples ascertained via agency involvement1-4
(with CSA of greater severity occurring in more problematic family environments)
or from clinical populations1-3,5
(with higher rates of psychiatric illness and greater functional impairment).
Still, general population studies have confirmed findings from these samples
including increased risk for psychiatric illness (anxiety disorders,6-11
depression,6-7,9-10,12-14
alcohol abuse and/or dependence,6-7,9-11,14-15
drug abuse and/or dependence,6-7,10
eating disorders,7, 14, 16
conduct disorder,6-10
and borderline personality disorder17) and
other adverse outcomes (suicide attempt,6, 14
current smoking,18 sexual revictimization,16, 19-20 and relationship
problems12, 14, 16, 20-21)
associated with self-reported CSA. Most studies have used retrospective designs
(ethically mandated interventions preclude entirely naturalistic, prospective
approaches), and are, therefore, subject to retrospective reporting bias.
One study6 that assessed psychiatric diagnoses
prospectively during adolescence and CSA history (required to have occurred
before the age of 16 years) retrospectively at the age of 18 years found increased
rates of subsequently occurring psychiatric disorders, particularly when CSA
involved intercourse.
Disentangling direct CSA effects from family background risk factors
has proved challenging since traditional case-control designs may inadequately
control for family background overestimating the effects of CSA. Investigators6-7,14, 16, 20-21
who have used statistical controls for family environment have reported that
risks associated with CSA involving intercourse remained significant, but
were much reduced in magnitude; results for less severe CSA were more unclear.
A meta-analysis of studies in college student samples argued that CSA has
limited importance beyond that attributable to the family environment.22
Investigators23-24 have
recently examined these issues in twin pairs, focusing on those discordant
for CSA. Because twins share family background risk factors, within-pair differences
in CSA-discordant pairs are assumed to have resulted either from CSA, or less
plausibly, from risk factors correlated with CSA that are not shared by pair
members. A mailed questionnaire survey assessed CSA history in Virginia female
like-sex pairs24 in whom psychopathologic status
had been previously assessed. In discordant pairs, the twin reporting CSA
involving intercourse had significantly increased risk of depression, alcohol
dependence, and having 2 or more psychiatric disorders. An interview study23 in the older Australian twin panel found a significant
difference in adverse outcomes between CSA-positive (ie, those individuals
who reported having experienced CSA) and CSA-negative (ie, those who denied
having experienced CSA) co-twins only for suicidal ideation in male subjects.
Because almost every odds ratio (OR) exceeded unity in both studies, the relatively
few discordant pairs may have limited power to detect differences. Both samples23-24 contained largely middle-aged respondents
who were considerably removed from the age of CSA occurrence. The Australian
study23 determined CSA status from a single
question about forced sexual activity.
The twin study design provides a means of distinguishing direct CSA
effects from correlated family background effects. If CSA-correlated family
background effects influence outcomes, then significantly higher risk would
be expected for nonabused twins whose co-twins were abused than for members
of pairs where neither was abused. The Australian study23
found significantly increased risk for nonabused individuals with CSA-positive
co-twins only for social phobia in women and conduct problems in men; confidence
intervals (CIs) were broad because of the small sample sizes. The Virginia
study24 instead controlled for a limited range
of parental variables concluding that family background risk factors play
a relatively unimportant role in the observed associations.
Using data from a new, younger Australian twin sample, with a more thorough
CSA assessment, we examined the extent to which CSA outcome associations are
determined by correlated family background risk factors vs direct CSA effects.
The sample includes both female and male like-sex twin pairs; the examined
negative outcomes were not limited to psychiatric disorders.
SUBJECTS AND METHODS
SUBJECTS
Subjects were members of the young adult cohort of the Australian Twin
Register, a volunteer twin panel born between January 1, 1964, and December
31, 1971. Almost all were registered with the panel between 1980 and 1982
by their parents in response to approaches either through school systems or
mass media appeals. All data reported herein are from a comprehensive assessment
completed from February 1996 through September 2000 by trained lay interviewers.
Verbal consent was first obtained from participants as per the protocol approved
by the institutional review boards of Washington University, St Louis, Mo,
and Queensland Institute of Medical Research, Brisbane, Australia. Of 4010
pairs that could be traced, interviews were completed with both members of
2765 pairs (69% pairwise response rate) and 1 member of an additional 735
pairs. The most common reasons for nonparticipation included refusal by twin,
incapacitation and/or death, and lack of available contact information. Singletons,
661 opposite-sex pairs, and pairs in which either member gave no response
to CSA items or responded problematically (see the "Assessment of CSA" section)
were excluded from analyses reported herein. The current sample included the
remaining monozygotic and dizygotic same-sex pairs (N = 1991) in which both
twins responded to at least 1 CSA component question. The sample was 58.2%
female and had a mean (SD) age of 29.9 (2.5) years. Twins were asked for the
"age at which they first lived apart"rather than whether they were raised
together. The 19 individuals (0.5%) who reported having first lived apart
before the age of 14 years included both members of only 3 pairs. Because
of the ambiguous wording and the relatively few like-sex twin pairs involved,
no twin pairs were excluded on this basis.
ASSESSMENT OF CSA
The current analyses focus on 5 questions about CSA (Table 1) from which, consistent with other reports,19
a composite CSA variable was developed for use in further analyses. Data from
43 pairs were excluded from all analyses because at least 1 twin endorsed
a CSA item (other than having been raped, see "Assessment of Outcome Measures
and Covariates" section) but reported an onset age of 18 years or older for
all endorsed CSA items. Data from 8 pairs, in which 9 of 13 CSA-positive individuals
failed to provide an age of CSA occurrence, were retained in the analyses.
Childhood sexual abuse was considered to have involved intercourse if respondents
reported having been raped before the age of 18 years. Missing data on the
occurrence of rape (n = 4) or its onset and recency (n = 4) in 8 CSA-positive
subjects led to their exclusion from analyses incorporating either CSA involving
intercourse or rape at the age of 18 years or older.
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Table 1. Component Childhood Sexual Abuse (CSA) Questions, Endorsement
Rates, and Risk by Gender*
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ASSESSMENT OF OUTCOME MEASURES AND COVARIATES
A standardized psychiatric diagnostic assessment, an adaptation of the
Semi-Structured Assessment for the Genetics of Alcoholism (SSAGA),25 was administered via telephone. The interview enabled
lifetime DSM-IV26
diagnoses of major depressive disorder, conduct disorder, and alcohol and/or
nicotine dependence. Nondiagnostic sections included questions about marital
history, contemplated or attempted suicide, traumatic events, parental alcohol-related
problems, family background, and "social anxiety" ( 1 social fear causing
impairment in functioning). Rape occurring at the age of 18 years or older
was included as an outcome measure.19 Divorce
was examined conditional on having been married. Onset information was obtained
for all outcomes other than divorce.
Maternal and paternal alcohol-related problems were assessed by a single
question asked about each parent. Other measures of family background risk
factors included as control variables in some analyses were (1) parental fighting,
coded positive if parents "often" fought or argued in the twin's presence;
(2) parental conflict, coded positive with report of "a lot"of conflict and
tension between parents when the twins were between the ages of 6 and 13 years;
(3) stepparent presence, that is, having been raised by a stepparent or adoptive
parent during part of childhood; (4) neglect, a composite variable reflecting
any positive response to "serious neglect," usually punished by either parent
in a harsh nonphysical way, or necessary medical therapy not provided after
injury; and (5) physical abuse, a composite variable reflecting any positive
response to physical abuse, purposely hurt by an adult relative, or hit by
either parent so hard that it "often" or "sometimes" hurt the next day. To
minimize retrospective recall bias, covariates were coded to reflect a positive
response by either twin.
DATA ANALYSIS
Primary statistical analyses were performed using SAS27
and the Stata Statistics and Data Analysis Package (version 6.0).28 An  level of .05 was required for statistical
significance. The robust variance estimator option in Stata (Stata Corp, College
Station, Tex) was used to obtain 95% CIs adjusted for the statistical nonindependence
of twin-pair observations. Childhood sexual abuse risk associated with the
respondents' responses to questions about their parents' problematic drinking
was examined. To investigate possible reporting bias, a logistic regression
was performed that examined CSA risk via the use of dummy variables coded
to represent respondents' and co-twins' responses to parental drinking items.
Comparisons were made between the age at onset of outcomes and CSA occurrence.
Survival analysis was performed separately by gender using Cox proportional
hazards regression models to calculate hazard ratios representing the risks
for adverse outcomes associated with prior occurrence of CSA. Logistic regression
models that controlled for gender were fitted to test for indirect, family
background contributions to the associations between outcome measures and
the respondent's and co-twin's CSA histories. These analyses used dummy variables
coded to represent whether respondents reported CSA involving intercourse
and for CSA-negative respondents, whether the co-twin was CSA-positive. Members
of pairs in which neither twin reported CSA served as the control group for
these analyses. Analyses were then repeated including family background variables.
Conditional logistic regression was used to determine the relative risks for
adverse outcomes in the CSA-positive vs CSA-negative members of discordant
twin pairs. Additional conditional logistic analyses were performed to determine
whether estimates of intrapair risk differed by gender, zygosity (ie, monozygote
or dizygote), or whether CSA involved intercourse.
RESULTS
All putative CSA component items were more commonly endorsed by women
(Table 1). Of 477 subjects who
endorsed at least 1 of these items, 67 (14.0%) endorsed 1 item, 156 (32.7%)
2, 190 (39.8%) 3, 59 (12.4%) 4, and 5 (1.0%) 5; the mean (SD) was 2.54 (0.92)
items. The Cronbach coefficient values were 0.79 (overall and women)
and 0.75 (men). Given very good internal consistency, the overlap of endorsement
across these nonmutually exclusive items, and the report's focus on comparison
of discordant pairs, a dichotomous composite variable representing endorsement
of at least 1 of these items, henceforth referred to as CSA, was deemed appropriate
for use in further analyses. Prevalence rates for CSA were 16.7% and 5.4%
for women and men, respectively.
A history of CSA was reported by 31.9% of those reporting vs 11.1% of
those denying maternal alcohol-related problems (OR, 3.75; 95% CI, 2.62-5.36)
and 19.5% reporting vs 9.5% denying paternal alcohol-related problems (OR,
2.32; 95% CI, 1.85-2.91). When co-twins' reports were also incorporated into
a logistic model, the ORs for self-reported CSA were as follows: for both
twins reporting maternal alcohol-related problems, OR 3.09 (95% CI, 1.79-5.33);
respondent only reported maternal alcohol-related problems, OR 4.50 (95% CI,
2.79-7.25); and co-twin only reported maternal alcohol-related problems, OR
2.08 (95% CI, 1.19-3.65). Similar values for paternal alcohol-related problems
were as follows: both twins reporting 2.62 (95% CI, 2.00-3.45); respondent
only, OR 1.87 (95% CI, 1.31-2.68); and co-twin only, OR 1.25 (95% CI, 0.83-1.87).
The fact that CSA was more strongly correlated with the respondent's report
of maternal alcohol-related problems (Wald  21 =
8.47, P = .004) with a similar trend for paternal
alcohol-related problems (Wald 21 = 3.59, P = .06) indicates that a mild retrospective recall bias
is contributing to the associations.
Childhood sexual abuse began early (mean [SD] age at onset 10.8 [4.06]
years), generally preceding the onset of adverse outcomes. Childhood sexual
abuse onset predated that of social fears by a mean of 1.7 years (95% CI,
0.3-3.1) and suicide attempt by a mean of 8.9 years (95% CI, 7.1-10.7). Childhood
sexual abuse's onset similarly predated the onset of each of the following
examined psychiatric disorders: conduct disorders by a mean of 1.7 years (95%
CI, 0.4-3.0); major depressive disorder by a mean of 10.3 years (95% CI, 9.3-11.2);
alcohol dependence by a mean of 10.5 years (95% CI, 9.4-11.6); and nicotine
dependence by a mean of 10.6 years (95% CI, 9.7-11.4).
When survival analysis was used to examine the risk for adverse outcomes
subsequent to reported CSA occurrence, significantly increased hazard ratios
were found in women for all examined outcomes and in men for all but divorce
and social anxiety (Table 2). The highest risks were for conduct disorder, suicide attempt, and rape at
the age of 18 years or older.
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Table 2. Prevalence Rates for Adverse Outcomes by Childhood Sexual
Abuse (CSA) History and Hazard Ratios Reflecting the Risk for Outcomes Associated
With Previously Occurring CSA*
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Adverse outcome risks were examined as a function of the extent of CSA
reported by the respondent (whether intercourse was involved) and, in CSA-negative
respondents, whether the co-twin reported having experienced CSA. As demonstrated
by the ORs reflecting their comparison to individuals from CSA-negative concordant
pairs (Table 3), those reporting
a history of CSA involving intercourse had the highest risks for all examined
adverse outcomes, which were significantly greater than those for either group
of CSA-negative respondents and exceeding those for individuals positive for
CSA not involving intercourse for all outcomes other than major depression
and social anxiety. Their risks were highest for conduct disorder, suicide
attempt, and rape at the age of 18 years or older with respective ORs of 14.53
(95% CI, 8.58-24.60), 14.64 (95% CI, 9.18-23.34), and 10.03 (95% CI, 5.66-17.81)
vs individuals from CSA-negative concordant pairs. Those reporting a history
of CSA not involving intercourse had significantly higher risks for all adverse
outcomes other than divorce when compared with individuals from CSA-negative
concordant pairs. Consistent with the hypothesis of a significant family background
effect, CSA-negative respondents whose co-twin was CSA-positive also had significantly
higher risks for all adverse outcomes other than major depression and divorce
when compared with members of CSA-negative concordant pairs. The risks for
CSA-positive individuals for whom abuse did not involve intercourse exceeded
those for CSA-negative, co-twin-positive individuals only for major depression
and social anxiety. When these analyses were repeated controlling for family
background variables, ORs were attenuated to varying degrees but the aforementioned
pattern largely remained. Despite controlling for these family background
variables, increased risk was still observed for CSA-negative, co-twin-positive
individuals for 5 of 8 outcomes.
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Table 3. Adverse Outcomes as a Function of the Childhood Sexual Abuse
(CSA) History of Respondent and Co-twin*
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When conditional logistic regression was used to examine the relative
risks for adverse outcomes in the CSA-positive vs the CSA-negative members
of CSA-discordant pairs, increased risks were noted for all of the examined
adverse outcomes (Table 4). Odds
ratios for this intrapair comparison ranged from 1.56 for major depression
(95% CI, 1.06-2.29) and alcohol dependence (95% CI, 1.01-2.40) to 7.50 (95%
CI, 1.72-32.80) for divorce. Three separate discordant pair analyses (results
not given) that examined whether estimates of intrapair risk differed by gender,
zygosity, and the extent of CSA (if intercourse was involved) reported by
the CSA-positive pair member found no significant differences.
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Table 4. Within-Pair Comparison of Adverse Outcome Risks in Childhood
Sexual Abuse (CSA)–Postive vs CSA-Negative Members of 283 Same-Sex Discordant
Pairs*
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COMMENT
In this large twin study, we found that individuals reporting a history
of CSA had increased risk for subsequently occurring adverse outcomes of depression,
suicide attempt, conduct disorder, alcohol and/or nicotine dependence, social
anxiety, rape after the age of 18 years old, and divorce. Our data suggest
that CSA occurs in the context of family background risk factors that contribute
to adverse outcome risk. We provide strong evidence that CSA is associated
with substantial risk not explained by these factors.
The association of CSA with risk for negative outcomes has been extensively
documented.1-21,23-24
In survival analyses, we observed consistently elevated hazard ratios affirming
that CSA is associated with increased risk for subsequently occurring negative
outcomes in women and men; hazard ratios were highest for conduct disorder,
rape after the age of 18 years, and suicide attempt. We relaxed the criterion
that outcomes must occur subsequent to CSA in further analyses to facilitate
comparisons within our report and with the literature, and because of onset-determination
issues (eg, less severe CSA often predated CSA involving intercourse).
In the comparison of outcomes as a function of the respondent's and
co-twin's CSA history, the highest risks for adverse outcomes were associated
with CSA involving intercourse, a replication of other reports.6-7,10, 16, 21, 24
With control for family background risk factors, these risks were diminished
to varying degrees but remained significant. Individuals who reported CSA
not involving intercourse had increased risk for all outcomes except divorce;
significance was retained (other than for social anxiety) with control for
family background risk factors.
The results of comparisons involving CSA-negative individuals whose
co-twins were CSA-positive deserve further discussion. These individuals displayed
significantly greater risk for most outcomes than members of CSA-negative
pairs, strong evidence that the family backgrounds of those who experience
CSA are also, on average, associated with considerable risk. However, despite
controlling for family background risk factors that included parental alcohol-related
problems, fighting, and conflict, presence of a stepparent, physical abuse,
and neglect, many of these risks retained significance. Moreover, few significant
differences were found with comparison to CSA-positive, intercourse-negative
respondents. A recent examination29 found that
unreliability in CSA reporting largely consisted of false-negative reports
in CSA-positive individuals. Similar reporting problems in our sample might
explain these findings, particularly if CSA false-negative respondents were
more forthcoming about psychosocial outcomes. The closeness of twin relationships
could have further blurred distinctions if the nonabused twin's supportiveness
led to greater co-twin resiliency at some personal cost. Alternatively, the
pattern of risks retaining significance in CSA-negative, co-twin-positive
individuals suggests that we may have inadequately controlled for familial
risk factors associated with impulsivity and substance abuse. Because all
ORs were higher (though not significantly so) for CSA-positive, intercourse-negative
individuals than CSA-negative, co-twin CSA-positive individuals, the lack
of significance for these comparisons may have resulted from limited power.
In discordant pairs analyses, we observed significantly greater risk
for all 8 examined adverse outcomes in CSA-positive respondents vs their CSA-negative
co-twins. Because data from CSA false-negative reports would reduce risk estimates,
our values are likely conservative. Despite the aforementioned finding of
greater risks associated with CSA involving intercourse, we observed no significant
heterogeneity of conditional ORs as a function of CSA severity in these discordant
pair analyses. Greater levels of family background risk factors occurring
in association with CSA involving intercourse may have contributed to our
difficulty distinguishing risks associated with less severe CSA. Discordant
pair analysis appears to provide an effective means of controlling for family
background risk factors across a range of CSA severity.
Two prior twin studies23-24
used discordant pair analyses to estimate the association between CSA history
and negative outcomes. Although few comparisons reached significance in either
report, the ORs for the same outcomes essentially fall within our study's
95% CIs. Presumably, because these studies included considerably fewer discordant
pairs, their power to detect differences was limited. One investigation23 also found no significant zygosity effect in discordant
pair analyses.
General population studies6-7,14, 16, 20-21
have attempted to control for family background factors by identifying important
predictors and entering them as control variables in regression models. They
typically have reported risks for adverse outcomes associated with CSA to
be preserved but considerably decreased in magnitude. This approach may have
been overly conservative with considerable correlation of predictor variables
(collinearity), including CSA history, limiting significance. In controlling
for family background risk factors, we accepted either twin's report of their
presence to minimize retrospective recall bias. By definition, this approach
could not alter discordant pair analysis results. As noted, we found evidence
persisted for family background effects notwithstanding the inclusion of control
variables into the logistic models.
Despite our cutoff for CSA (age 18 years) being the highest limit used
commonly,3 our sample's mean age of CSA occurrence
(10.8 years) is similar to values previously reported.2-3,11, 30-31
The prevalence of CSA in our sample is consistent with that for contact CSA
in general population samples.2-3,30-35
Our rates for CSA involving intercourse were essentially identical to those
in a New Zealand study.32 Previous reports
have also found higher CSA rates associated with parental alcoholism2-3,32-33,35
and female gender3, 8, 10, 23, 30-32,34
with smaller gender differences when abuse involved extrafamilial perpetrators.30
Associations between self-reported CSA and earlier smoking initiation
and heavier tobacco use have previously been reported.36
A positive relationship has been found between the total number of adverse
childhood experiences and risk for subsequent smoking behavior.18
Our finding that, controlling for family background risk factors, self-reported
CSA is associated with significantly increased nicotine-dependence risk is
a logical extension of these results.5, 18, 36
Our results must be interpreted in the context of potential biases from
the following sources: (1) retrospective reporting, (2) CSA definition, (3)
sample selection, and (4) assumptions made in control for family background.
A bias would result from the use of retrospective self-report data if individuals
currently experiencing problems were more likely to recall prior abuse, resulting
in an inflation of the observed associations. However, a recent examination29 of the stability of CSA reports found no relationship
between variations in reports and psychiatric status before, during, or after
the reported abuse. The greater CSA risk observed with respondents' vs co-twins'
report of parental alcohol-related problems could indicate greater willingness
for CSA survivors to acknowledge negative aspects of childhood. Onset-dating
inaccuracies may have occurred, but would not be expected to systematically
bias results.
The level of internal consistency displayed by component items, coupled
with the necessity of a binary measure for discordant pair analyses, provide
adequate rationale for our composite CSA variable. Although consistent with
other studies,19-20 our use of
a cutoff date (respondents'18th birthday) before which forced intercourse
was considered CSA and after which, rape at the age of 18 years old or older
would have included abuse persisting into adulthood under both categories,
amplifying the association with rape after the age of 18 years. We required
conservatively that contact be forced if it involved either another child
within the family or someone outside the family at least 5 years older. Those
who have suggested22 that males suffer less
consequences after CSA may object to combining data across gender, however,
we found no evidence for a significant gender effect.
A selection bias may have arisen from the panel's initial recruitment
since parents aware of abuse may have been less likely to volunteer their
twins. The similarities of CSA prevalence and characteristics to other reports2-3,30-35
suggest that this bias was limited. Similarly, it is unlikely that telephone
assessment introduced any substantial bias over face-to-face32
approaches. Our exclusion of pairs in which either twin was not interviewed
could have eliminated the most severely abused individuals reducing the magnitude
of effects attributed to CSA. A post hoc examination including data from same-sex
twins with noninterviewed co-twins revealed that CSA-positive women were actually
more likely to belong to pairs where both twins were interviewed; no significant
differences were observed for male subjects.
We controlled for family background risk factors between rather than
within pairs to minimize reporting bias. However, the CSA-positive twin may
have received a larger dose of trauma or differentially negative treatment.
Alternatively, additional stressors may have had a larger influence on either
twin. Our approach could have biased estimates in either direction. Finally,
we cannot infer a causal link from results for CSA-discordant pairs. It remains
possible that other unmeasured risk factors, for which the twins are discordant,
predict both increased risk of CSA and other outcomes.
In the largest sample of CSA-discordant same-sex pairs thus evaluated,
we observed significantly greater risk for all 8 examined adverse outcomes
in CSA-positive respondents vs their co-twins. The most straightforward interpretation
of our results is that there is a direct association between CSA and risk
for adverse outcomes. We also provide evidence that family background risk
factors contribute increased negative outcome risk. These findings demonstrate
the considerable potential of sibling studies for dissecting the direct and
correlated family background effects associated with CSA.
AUTHOR INFORMATION
Accepted for publication June 26, 2001.
This work was supported by grants AA00277 (Dr Nelson) and AA07728, AA10249,
and AA11998 (Dr Heath) from the National Institutes of Health, Bethesda, Md,
and grants 941177 and 981351 (Dr Martin) from the Australian National Health
and Medical Research Council, Canberra.
Corresponding author and reprints: Elliot C. Nelson, MD, Washington
University School of Medicine, Department of Psychiatry, 40 N Kingshighway,
Suite 1, St Louis, MO 63108 (e-mail: nelsone{at}psychiatry.wustl.edu).
From the Department of Psychiatry, Washington University School of
Medicine, St Louis, Mo (Drs Nelson, Heath, Madden, Bucholz, Glowinski, and
McLaughlin); Department of Psychology, University of Missouri–Columbia
(Dr Cooper); Finch University of the Health Sciences–The Chicago Medical
School, North Chicago, Ill (Dr Dinwiddie); Queensland University of Technology,
Kelvin Grove, Australia (Dr Dunne); and Queensland Institute of Medical Research,
Brisbane, Australia (Ms Statham and Dr Martin).
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