Assessment of Characteristics of Intrusive Thoughts and Their Impact on Distress
Among Victims of Traumatic Events
ANGELA LIEGEY DOUGALL, MS, KARRIE J. CRAIG, PHD, AND ANDREW BAUM, PHD
Objective: This study examines the psychometric properties of the Intrusive Thoughts Questionnaire (ITQ) and its
utility as a predictor of distress among trauma victims. Method: Victims of three types of trauma, a motor vehicle
accident (N 5 115), a hurricane (N 5 182), and recovery work after an airline disaster (N 5 159), completed the ITQ
along with the Impact of Event Scale (IES) and the Symptom Checklist-90, Revised (SCL-90-R), at several different
time points after their exposure. Results: The ITQ was a reliable and valid instrument that was positively related
to concurrent measures of distress as well as a predictor of long-term stress responding. Characteristics of intrusive
thoughts reflecting the extent to which they were unwanted or controllable, were identified as key determinants of
distress. Conclusions: The ITQ is a useful adjunct to current measures of intrusions, allowing for greater specificity
in analyses of responses to trauma. Evaluation of characteristics of intrusions indicated that frequency of intrusions
was neither the only predictor of distress nor the best predictor of trauma-related outcomes. Key words: intrusive
thoughts, trauma, stress, assessment.
ITQ 5 Intrusive Thoughts Questionnaire; IES 5 Im-
pact of Event Scale; SCL-90-R 5 Symptom Checklist-
90, Revised; PTSD 5 posttraumatic stress disorder;
MVA 5 motor vehicle accident; GSI 5 global severity
index.
INTRODUCTION
Intrusive thoughts are often negative, upsetting, and
stressful. These thoughts, images, or memories are not
only hallmark symptoms of PTSD but occur frequently
after a wide range of stressful events. They may reflect
ongoing coping and mental processing of stressful ex-
periences, failed adaptation, overconsolidated memo-
ries, or general disturbance, and they may serve to
promote continued stress responding (eg, Refs. 1–3).
Unwanted and unbidden thoughts about a stressful
experience seem to be important predictors or anteced-
ents of the costs of many stressors. Present measures of
intrusive thoughts have been useful, but are primarily
limited to assessment of the frequency of intrusions.
To determine whether other aspects of intrusive expe-
rience affect the intensity and/or duration of traumatic
stress, an inventory was developed that assesses sev-
eral characteristics of these intrusions. The frequency
of intrusions, the presence of cues, the extent to which
intrusive thoughts are unwanted and disturbing, and
their manifestations during sleep were measured in
three independent samples of trauma victims. This
paper describes the inventory and preliminary evi-
dence of its reliability and validity.
Intrusive thoughts are not a new construct; Freud
suspected them as a cause of distress and they have
been characterized in several psychodynamic systems
(4, 5). They have received considerable empirical at-
tention in the past 20 years, in part because persistent
intrusions are an essential characteristic of PTSD (6).
They are usually defined as unbidden, uncontrollable,
and generally unwanted thoughts or images of a past
event, an anticipated event, or of some other stimulus
or situation (2). They are characteristic of several psy-
chiatric disorders, but they do not occur exclusively as
part of a disorder. Many people report intrusions after
a traumatic event, but the majority of these individuals
do not develop PTSD (7, 8). For most, intrusive
thoughts gradually decrease to very low levels (3, 8).
Intrusive thoughts need not be negative or associ-
ated with a stressor; they may be neutral or positive
and can occur in many benign situations (9). However,
the uncontrollable or unpredictable nature of intrusive
thoughts may be stressful. Intrusive recollections, im-
ages, and other representations of a stressor seem to
contribute to the persistence of chronic stress (1). They
also seem to be related to several stress-related biolog-
ical outcomes, including resting blood pressure and
adrenal activity (eg, Refs. 1, 10). They are ordinarily
transient and often identifiable only after they have
occurred, making them very difficult to measure. Their
significance for stress, mental health, and overall well
being suggests that innovative approaches to their in-
vestigation are warranted.
The most commonly used measure of intrusive
thoughts is the IES (2). This 15-item instrument has
good test-retest reliability and yields an overall score
and values for subscales that address intrusions (Cron-
bach’s a 5 .78) and avoidance (Cronbach’s a 5 .82).
The IES has been widely used in studies of community
disasters and individual traumas (eg, tornados, floods,
From the University of Pittsburgh Cancer Institute, Pittsburgh,
Pennsylvania.
Address reprint requests to: Andrew Baum, University of Pitts-
burgh Cancer Institute, Department of Behavioral Medicine and
Oncology, 3600 Forbes Ave., Suite 405, Pittsburgh, PA 15213.
E:mail: baum@pcicirs.pci.pitt.edu.
Received for publication March 9, 1998; revision received July 23,
1998.
38 Psychosomatic Medicine 61:38–48 (1999)
0033-3174/99/6101-0038
Copyright © 1999 by the American Psychosomatic Society

motor vehicle accidents, rape; Refs. 8, 11, 12). Most of
the data we have about the experience and effects of
intrusions has been derived from this instrument. The
IES has also been studied extensively in conjunction
with formal diagnoses of PTSD and has been used as a
proxy for a diagnostic interview. A recent revision of
the IES by Weiss and Marmar (13) includes seven
symptoms of hyperarousal, another key feature of
PTSD. Additionally, the response format has been
changed in the new version from frequency of symp-
toms on a 0, 1, 3, or 5 scale to amount of distress on a
0 to 4 scale.
Although the IES has been extremely useful in il-
lustrating the importance of intrusions, it does not
provide much information about intrusive experi-
ences. There are many facets to the experience of trau-
ma-related intrusions. Information obtained on each of
these characteristics should improve our ability to pre-
dict long-term outcomes after a trauma over that ex-
plained by a single dimension, such as frequency of
intrusions as seen with the IES. One can identify at
least six variable dimensions of intrusions that may
contribute to overall distress: 1) the frequency of in-
trusive thoughts; 2) the predictability or occurrence of
these thoughts in the presence or absence of cues;
3) whether intrusions are negative and/or upsetting;
4) the degree to which these thoughts are unwanted;
5) the extent to which intrusions are controllable once
they occur; and 6) the extent to which they occur as
dreams during sleep. Previous research has suggested
that these characteristics of intrusive thoughts are re-
lated to stress and mental health outcomes (eg, A.B.,
unpublished data, 1998). The ITQ was developed to
measure these characteristics of intrusive thoughts.
The ITQ yields a composite score that reflects overall
disturbance associated with intrusions that should be
highly correlated with the IES-Intrusion score.
Items for the ITQ were selected and/or discarded
over several years of developing a general item base for
the inventory. Largely drawn from clinical experiences
and research on disasters, the original pool of items
was reduced after examination of item frequencies and
correlations among items when subsets of the items
were given to participants in several disaster studies.
Once constituted, the ITQ was administered to partic-
ipants of three ongoing studies of victims of three
types of trauma: MVAs, a major hurricane, and rescue
and recovery work after an air disaster. In two of these
samples (the MVA victims and the airplane crash
workers), the ITQ was administered four times over
the course of the year after the event. It was expected
that reports of intrusions would decrease with the
passage of time. As part of these larger studies, several
other measures were administered allowing compari-
son of the ITQ to scores on the IES (2) and the SCL-
90-R (15). These comparisons allowed assessment of
the convergent, discriminant, and predictive validity
of the ITQ.
METHOD
Participants
Data were drawn from ongoing studies of three types of traumatic
events. Samples of MVA victims, disaster victims, and emergency
workers from the crash of Flight 427 were studied.
Motor Vehicle Accident Study. Victims of MVAs (N 5 115) were
recruited from either a regional trauma center in a large middle
Atlantic metropolitan area or local police reports of MVAs. Individ-
uals were considered for study participation if they were admitted to
the trauma center or another area emergency room or trauma unit.
Experimenters contacted all potential participants after discharge
from the hospital. Approximately 44% of all eligible candidates
agreed to participate.
A control group of 42 participants was recruited from among
emergency room patients at the same hospital as the MVA victims.
All of these individuals presented with minor injuries (eg, broken
leg, sprained wrist, lacerations). Otherwise comparable to the MVA
sample, these participants were considered to have experienced a
low-threat injury and could not have been in a MVA in the past 5
years. The final sample was 52% female with a mean age of 35 years
(range, 18–64) and a median education of some advanced schooling.
Racial composition reflected the racial make-up of the surrounding
communities and consisted of participants who identified them-
selves as Caucasian (76%), African American (14%), Hispanic (6%),
Asian American (1.5%), or from another race (3%). Participants
were seen four times over the course of a year, 2 to 3 weeks after the
accident, and then 3, 6, and 12 months afterward. About a third of
the sample failed to complete all four assessments.
Hurricane Andrew Study. Participants were recruited from Dade
County in South Florida, which was devastated by Hurricane Andrew.
The sampling areas included some of the most heavily affected areas of
the county. Because of the magnitude of destruction associated with the
storm (eg, homelessness/relocation, sustained phone and power inter-
ruptions, uninhabitable homes), it was difficult to locate potential
subjects by phone or mail. Alternative methods of subject recruitment
were used: flyers were handed out in shopping centers and neighbor-
hoods, the research team went into affected neighborhoods knocking
on doors, and affected staff at local universities and colleges were
contacted regarding possible participation in the study; 183 subjects
were recruited using these methods. However, one subject was ex-
cluded because she did not read well enough to complete the question-
naires. The final sample included 119 women and 63 men with an
average age of 39 years (range, 18–80) and a median education level of
some college or advanced training. Comparison with census data from
1990 suggested that the cultural diversity of the South Florida area was
reflected in the sample: 44% of the sample was Caucasian, 34% was
African American, 18% was Hispanic, and 4% was from other ethnic
groups.
USAir Flight 427 Study. On September 8, 1997, USAir Flight 427
crashed outside of Pittsburgh, Pennsylvania, exploding on impact
and killing all 132 crew and passengers on board. The nature of the
crash, the terrain, and working conditions made the recovery and
cleanup effort very stressful. A total of 159 workers at the crash site
and a control group of 41 occupation-matched participants who did
not participate in the cleanup were recruited. Initial contacts were
made through supervisors of medical, emergency response, and
airport staff of units directly involved at the crash site. Unit members
INTRUSIVE THOUGHTS QUESTIONNAIRE
39Psychosomatic Medicine 61:38–48 (1999)