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Psychometrics of Impulsive Aggression
Prepared by Eric Youngstrom, Ph.D. & Robert L. Findling, M.D.
Method
Source Data: The following analyses are based on secondary analyses of data collected under the
auspices of a Center Grant from the Stanley Medical Research Institute (PI: Robert L. Findling,
M.D., and Joseph R. Calabrese, M.D.). The data files used in this reanalysis were previously
published (Youngstrom et al., 2004), and details about the recruitment strategy and participants
are presented there.
Measures: The data file included item scores on four relevant measures: The Parent General
Behavior Inventory (P-GBI) (Youngstrom, Findling, Danielson, & Calabrese, 2001), the Young
Mania Rating Scale (YMRS) , the Achenbach Child Behavior Checklist (CBCL), and the
adolescent self-report of the General Behavior Inventory (A-GBI). The primary caregiver
completed the P-GBI and CBCL at the initial evaluation for all youths ages 5 to 17 years (N =
642). The YMRS was completed by a highly trained rater based on direct interview of both the
parent and the youth (ages 5 to 17). Adolescents ages 11 to 17 years completed the A-GBI (n =
324).
Internal Consistency of Impulsive Aggression Items
Latent class analyses of the ratings by three experts identified eight items as assessing impulsive
aggression on the A-GBI and P-GBI. These included items #27, 42, 44, and 51 from the
depression scale, and #14, 39, 53, and 54 from the hypomanic/biphasic scale. In the present data,
correlations among these items reflected a single underlying dimension according to the three
most accurate decision rules for determining the number of factors: the Scree test, the Minimum
Average Partials method, and Glorfeld’s extension of Horn’s Parallel Analysis. The eight items
on the P-GBI showed good internal consistency, with Cronbach’s alpha = .87. Alpha was .88 for
the same items based on adolescent self report.
Ten items (#20, 21, 37, 57, and 95 unanimously; and #16, 41, 87, 97, and 104 by two out of three
judges) were identified as measuring impulsive aggression on the CBCL. Again, this set of items
indicated a single factor according to all criteria examined, with alpha = .91.
Items #5 (irritable mood) and #9 (disruptive/aggressive behavior) from the YMRS measured
impulsive aggression, correlating r = .91 with each other.
Confirmatory Factor Analysis Across Measures
A confirmatory factor analysis tested whether a single factor of impulsive aggression drove the
relationships between the IA items drawn from each of the four measures. Based on maximumlikelihood estimation, a single factor solution provided acceptable fit to the data: X2 (2 df) =
7.74, CFI = .97. Standardized loadings on the IA factor were .48 for the A-GBI, .51 for the
YMRS, .79 for the CBCL, and .86 for the P-GBI.
Related to Jensen et al., Consensus Report: Impulsive Aggression as a Symptom Across Diagnostic Categories in
Child Psychiatry: Implications for Medication Studies. J Am Acad Child Adolesc Psychiatry 2007
IA Elevations Across Diagnoses
To investigate the level of IA associated with different disorders, participants were grouped by
primary Axis I diagnosis (as determined by KSADS interview and review by a physician). For
these purposes, a bipolar spectrum diagnosis (bipolar I, bipolar II, cyclothymia, or bipolar Not
Otherwise Specified) was considered “primary” regardless of comorbidity; then unipolar mood
disorders were put in a separate category, followed by ADHD and disruptive behavior disorders
(without comorbid mood disorder) and finally those youths not meeting criteria for any Axis I
disorder.
Oneway ANOVAs compared the average level of IA across these five groups (with bipolar I
examined separately from the other bipolar spectrum diagnoses), across all four measures (thus
N = 642 for the P-GBI, YMRS, and CBCL; and n = 324 for the AGBI). The Games-Howell
procedure was used for post-hoc comparisons, because it is robust to violations of the
assumption of homogeneity of variance (and the no diagnosis group had significantly lower
variance than any of the clinical groups across all measures).
The figure below summarizes the pattern of findings, presented in terms of raw scores on each
scale. The bipolar I and other bipolar spectrum groups did not differ in IA, and both bipolar
groups tended to show more IA than the unipolar or ADHD/disruptive behavior groups. All
clinical groups showed significantly more IA than the “no diagnosis” group, p < .05 based on the
Games-Howell tests.
14
12
10
8
6
4
2
0
PGBI Imp-Agg
AGBI Imp-Agg
Bipolar I
Disruptive Beh D/Os
YMRS Imp-Agg
Other Bipolar Spectrum
No Diagnosis (V71.09)
CBCL Imp-Agg
Unipolar Mood D/O
Latent Class Analyses of IA
Related to Jensen et al., Consensus Report: Impulsive Aggression as a Symptom Across Diagnostic Categories in
Child Psychiatry: Implications for Medication Studies. J Am Acad Child Adolesc Psychiatry 2007
Latent Class Analysis was performed on the 8 items from the P-GBI using the full data set (N =
624), using Latent Gold version 3.0.1 software. Based on examination of multiple model fit
criteria, three clusters were present in the data (L2 = 4089, df = 3,111,633, 7.5% classification
errors, and lowest relative AIC and BIC values compared to 1 or 2 through 10 cluster models).
The item score profiles were roughly parallel (as shown in the figure below), and the three
groups represented low, medium, and high levels of impulsive aggression.
4
3.5
3
Low
Medium
High
2.5
2
1.5
1
PGBI27 PGBI42 PGBI44 PGBI51 PGBI14 PGBI39 PGBI53 PGBI54
As shown below, more than 95% of cases with diagnoses of bipolar I (according to strict DSMIV criteria) showed moderate or severe IA, as did more than 90% of all other bipolar spectrum
cases. Two thirds of youths with unipolar depression and half of youths with ADHD or
disruptive behavior disorders also showed moderate or high IA, whereas fewer than 10% of
youths with no Axis I diagnosis showed even moderate levels of IA. The figure below details the
breakdown of levels of IA within each of the diagnostic groupings, using the eight PGBI items as
indicators.
Related to Jensen et al., Consensus Report: Impulsive Aggression as a Symptom Across Diagnostic Categories in
Child Psychiatry: Implications for Medication Studies. J Am Acad Child Adolesc Psychiatry 2007
100
90
80
70
60
50
40
30
20
10
0
Bipolar I
Cyclothymes,
BP II, BP
NOS
Unipolar
Mood D/O
Low
Disruptive
Beh D/Os
Medium
residual grab bag
No Diagnosis
(V71.09)
High
Latent class analyses were also performed on the 10 items from the CBCL. Based on the same
decision rules, a three cluster solution provided the best fit for these data as well. The breakdown
of IA levels across diagnostic groups is reported as Figure 2 in the main body of the manuscript.
Impulsive Aggression and Treatment Discontinuation
Another set of analyses examined the association between IA and treatment outcome, using data
from an open-label stabilization lead-in phase of a maintenance study for pediatric cases with
bipolar I (Findling et al., 2003***). These analyses were based on data from 130 youths enrolled
in the first phase. All participants in the stabilization phase received open-label combination
therapy with divalproex and lithium. Cox regression analyses tested whether any covariates
predicted the length of time until stabilization, as well as whether or not the patient was able to
continue onto the maintenance phase of the study. IA at the end of phase I was the only
significant predictor of treatment length, with higher IA indicating a greater risk of dropping out
from the study. When measured with the PGBI items, IA was associated with a regression
weight of -.15, Wald = 52.13, p < .0005. Although residual mood symptoms also predicted
greater risk of dropout, they were no longer significant after controlling for IA. People who
discontinued the study for any reason also had substantially higher average levels of IA than
people who were maintained in the study. For example, discontinuers had an average score of 5.5
on the PGBI IA scale, versus an average of 1.0 at end of phase for the persons able to continue to
the maintenance phase; F (1, 124 df) = 8.75, p = .004.
Related to Jensen et al., Consensus Report: Impulsive Aggression as a Symptom Across Diagnostic Categories in
Child Psychiatry: Implications for Medication Studies. J Am Acad Child Adolesc Psychiatry 2007
References
Youngstrom, E. A., Findling, R. L., Calabrese, J. R., Gracious, B. L., Demeter, C., DelPorto
Bedoya, D., et al. (2004). Comparing the diagnostic accuracy of six potential screening
instruments for bipolar disorder in youths aged 5 to 17 years. Journal of the American
Academy of Child & Adolescent Psychiatry, 43, 847-858.
Youngstrom, E. A., Findling, R. L., Danielson, C. K., & Calabrese, J. R. (2001). Discriminative
validity of parent report of hypomanic and depressive symptoms on the General Behavior
Inventory. Psychological Assessment, 13, 267-276.
Related to Jensen et al., Consensus Report: Impulsive Aggression as a Symptom Across Diagnostic Categories in
Child Psychiatry: Implications for Medication Studies. J Am Acad Child Adolesc Psychiatry 2007