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A brief screen for panic disorder
Pergamon
Journal of AnxietyDisorders,Vol.8, No. 1,pp. 71-78, 1994 Copyright0 1994 Elsevier Science Ltd Printedin the USA. AU rights reserved 0887-6185194 $6.00 + .OO
A Brief Screen for Panic Disorder WILLIAM J. APFELDORF,M.D., PH.D., M. KATHERINESHEAR, M.D., ANDREW C. LEON, PH.D., ANDLAURA PORTERA,B.A. Department of Psychiatry, New York HospitaVCornell University Medical College
Abstract - Panic disorder is associated with excessive social morbidity and linancial burden. Delay in its diagnosis is a serious problem confronting the health care system. Screening instruments can be used to alert clinicians to the presence of an illness. In the current study, 143 patients presenting to an outpatient anxiety disorders clinic completed both self-report scales and a structured clinical interview. The 16-item Anxiety Sensitivity Index (ASI) selectively discriminates panic disorder subjects from subjects with other anxiety disorders in an anxiety clinic population. Further analyses demonstrate that a scale composed of merely four ASI items also discriminates panic disorder patients with equal sensitivity and specificity to the overall instrument. This new composite scale, named Brief Panic Disorder Screen (BPDS), will allow rapid identification of those patients who may benefit from more extensive evaluation for the presence of panic disorder.
Panic attacks are sudden and spontaneous discrete periods of intense fear and anxiety associated with shortness of breath, dizziness, palpitations, nausea, or abdominal distress. During an attack, people often believe they are losing control, having a heart attack, or losing their minds. At least four of these attacks must occur within a four-week period, or at least one of the attacks must be followed by a month of persistent fear of having another attack to meet DSM-IIIR diagnostic criteria for panic disorder (American Psychiatric Association, 1987). People with panic disorder frequently believe that they have a severe physical illness and seek medical attention (Katon, 1984). Physicians tend to describe anxiety symptoms from the viewpoint of their own specialty (Skerrit, 1977). For example, cardiologists focus on atypical chest pain, pulmonologists on hyperventilation, and gastroenterologists on irritable bowel symptoms when, in fact, these various symptoms are actually manifestations of a panic disorder. This results in underdiagnosis of panic disorder (Katon, 1984). Delays in proper diagnosis are costly both the individual and the health care delivery system. The average medical costs per patient in the first nine years after panic Dr. Shear is now with the Departmentof Psychiatry, University of Pittsburgh. Correspondence should be addressed to Dr. Apfeldorf, Payne Whitney Clinic, New York Hospital/CornellMedical Center,525 East 68th Street, New York,NY 10021. This research was supported in part by me Reader’s Digest Fund (WJA). 71
72
W. 1.
ET AL.
onset have estimated to greater than (Anthony, Brown, Barlow, 1992). and active could reduce the psychological and financial of panic A structured assessment performed a trained is the accurate way determine if patient meets for a diagnosis. such an is impractical use with patient in general medical More efficient methods are to identify that merit comprehensive evaluation. comprehensive would confirm who clearly diagnostic criteria who should referred for Some diseases particularly important identify by widespread screenstrategy. Three for such have been (Wilson & 1968). Panic appears to all of criteria. First, disease should an important health problem a sizable portion of population. The Catchment Area Program found the lifetime of panic is 1.5% the general ulation of adults (Eaton, & Weissman, Second, there be period which the is present, unrecognized. For subjects with disorder, several elapse during panic symptoms not recognized part of disorder, yet impairment (Anthony, Brown, Barlow, 1992). addition, the Survey found 28.4% of with panic visited emergency for their problem, and sought only general medical (Klerman, Weissman, Johnson, & 1991). Third, should exist may be once the is estabMedication and approaches effectively both the and the of panic (NIH, 1991). Panic Disorder a good for the of a program. Investigators used self-report (Stewart, Hays, Ware, 1988; Ward, Mendelson, & Erbaugh, and structured interviews (Endicott Spitzer, 1978; Williams, Gibbon, First, 1990) screen for disorders. Self-report are easy administer; however, often are diagnostically specific. interviews are specific, but time and makes their difficult and A more approach is two-stage case strategy in a self-report is used select highpatients on a structured is then (Fleiss & 1989; Hoeper, Cleary, Regier, Goldberg, 1979). Disorder patients prone to fearfulness of sensations, of those associated with (McNally, 1990; 1991). Such is postulated play an role in disorder, to the model of disorder (Goldstein Chambless, 1978; 1986). The Sensitivity Index an operationalized measure of of bodily (ASI: Reiss, Gursky, & 1986; McNally Lorenz, 1987). Koch, and (1992) reported the AS1 among the anxiety disorders. scores assowith each the six anxiety disorders, the exception
73
A BRIEFSCREENFORPANIC DISORDER
simple phobia, were greater than those of normal subjects. AS1 scores associated with Panic Disorder were significantly higher than those with other anxiety disorders, with the exception of Post-Traumatic Stress Disorder, where there was a trend for the Panic Disorder score to be higher. In contrast, the State-Trait Anxiety Index - Trait did not discriminate among anxiety disorders. These investigators concluded that the AS1 measures a construct distinct from that measured by the State-Trait Anxiety Index - Trait, and that the AS1 can be used to discriminate anxiety disorder diagnoses. Other studies support the importance of anxiety sensitivity in panic disorder. In a longitudinal study, high AS1 scores predicted frequency and intensity of panic attacks three years later (Maller & Reiss, 1992). In a provocation paradigm, subjects with high anxiety sensitivity scores demonstrated enhanced reactions to a hyperventilation challenge (Donnell & McNally, 1989). To explore further the usefulness of the AS1 as a screening instrument for panic disorder, we replicated the findings of Taylor, Koch, and Crockett (1991) demonstrating the specificity of the AS1 for panic disorder. We then undertook a two-step analytic procedure to attempt to identify a subscale of AS1 items that might be useful as a screen for panic disorder.
METHODS Subjects One hundred forty-three outpatients who presented to the Payne Whitney Clinic Anxiety Disorders Clinic and who were diagnosed by structured interview (SCID) as having a primary anxiety disorder were participants in the study. The characteristics of the subject sample are presented in Table 1.
TABLE 1 CLINIC bPULAllON
primary
Diagnosis
A. Panic Disorder Panic Disorder + Agoraphobia Panic Disorder - Agoraphobia Total Panic Disorder
&ARAClERIS?lCS
NUIllber
Female
Age (SD)
85 8
79% 75%
38.9 (12.1) 41.0 (13.4)
93
78%
39.1 (12.2)
B. Other Anxiety Disorders Agoraphobia Social Phobia Simple Phobia Generalized Anxiety Disorder Obsessive Compulsive Disorder Post-Traumatic Stress Disorder Anxiety Disorder NOS
4 18 20 0 0
Total Other Anxiety Disorders
50
100% 29% 50% 61% 50%
33.3 (8.6) 51.8 (13.9) 49.4 (13.8) 37.1 (11.3)
52%
42.3 (13.6)
46
14
W. J. APFELDORF IT AL.
The 143 patients included 99 women and 44 men. The mean age of the subjects was 40.2 f 12.6 years. Ninety-three met DSM-III-R criteria for Panic Disorder with or without Agoraphobia. Fifty met criteria for a different primary anxiety disorder. Gender and age characteristics of each diagnostic group are presented in Table 1. Procedure Patients contacting the Clinic were screened by phone interview to determine the likely presence of an anxiety disorder. Patient evaluation included a questionnaire packet containing self-report scales and participation in a structured clinical interview. Patients agreeing to complete the questionnaires and interview signed informed consents. Psychometric responses and diagnoses were collected independently. Assessments The Anxiety Sensitivity Index is a 16-item self-report measure of fear of anxiety (Reiss et al., 1986). Responses to each item are made on a five-point Likert scale from “very little” to “very much.” AS1 total score is calculated by summing the 16 items, resulting in a possible range of 0 to 64. Representative items include “it is important to me not to appear nervous,” “it scares me when I become short of breath,” and “unusual body sensations scare me.” High scores represent greater fear of bodily sensations. Diagnoses were established using the Structured Clinical Interview for DSM-III-R (SCID, Spitzer et al., 1990). conducted by a trained rater. Testretest reliability of the SCID for the current diagnosis of panic disorder has been reported as X = 0.58, respectively (Williams et al., 1992). Data Analyses The ability of the AS1 to discriminate patients who met criteria for panic disorder (with and without agoraphobia) from those with other anxiety disorders was evaluated. The AS1 total scores for the two groups were compared using t-tests. We conducted further analysis in order to explore the possibility that a subset of questions might be used to identify panic disorder subjects. A stratified randomization procedure was used to generate two groups of subjects: an “index” sample and a “cross-validation” sample. The stratification was based on dividing the study sample into two groups: panic disorder patients and other anxiety disorder patients. Subjects in each of these groups were randomly assigned to either the “index” sample or the “cross-validation” sample. A two-step procedure was then used to select a subset of items that could comprise a brief screen. To identify AS1 items that best differentiated between panic disorder and other anxiety disordered subjects, a between-group effect size (ES) was calculated for each AS1 item. The ES is defined by Cohen (1992) as the ratio of the difference between group means relative to the pooled standard deviation. This quantity reflects the magnitude of the differ-
75
A BREF SCREEN FOR PANIC DISORDER
ence between the two groups relative to variability within each group. It is equal to the absolute value of the difference between group means, divided by the pooled standard deviation, 1jT1 - Ti;,I/ Spooled. Items with ES 2 0.80 were identified and included in the subscale, based on the proposal of Cohen (1992) for a “large” ES in a between-group f-test. An unweighted sum of those items formed the Brief Panic Disorder Screen (BPDS). These item analyses were conducted using the index sample. The internal consistency among the BPDS items was examined using Cronbach’s coefficient a (Cronbach, 1951) on the pooled index and cross-validation samples. The cross-validation sample was then used to contruct receiver operator characteristic (ROC) curves. These curves were used to select an optimal cutscore on the BPDS for case identification (Hsiao, Barko, & Potter, 1989). The ROC curve was used to compare the tradeoff between sensitivity and specificity of the various cutscores. Subjects scoring at or above the respective cutscores are classified as “cases,” and the others as “non-cases.”
RESULTS The Panic Disorder group (n = 93) had a mean AS1 score of 38.4 f SD 11.6. This was signilicantly higher than the Other Anxiety Disorder group (n = 50) mean score of 27.6 + SD 12.3 (p c 0.001). The stratified randomization of the subjects groups yielded an index sample (n = 82) and a cross-validation sample (n = 63), each containing 65% Panic Disorder subjects. Four AS1 items had large between-group effect sizes (ES 2 0.8) in the index sample. These four items form the new scale, the Brief Panic Disorder Screen (BPDS), and are listed in Table 2. The minimum score possible on the resulting four-item BPDS is 0 and the maximum score possible is 16. In the cross-validation sample, the panic disorder group had a mean score of 12.6 + SD 4.0. This is significantly higher than the other anxiety disorder group, which had a mean score of 7.5 + SD 4.1 (p < 0.001). Cronbach’s coefficient c1 for the BPDS is 0.875, indicating a high degree of consistency among the four items. The ROC curve for the new scale in the cross-validation sample is presented in Fig. 1. Note that as the cutscore increases, the false positive rate TABLE 2 BRIEFPANIC DISORDERSCALE
Please. rate each item by circling one of the five phrases for each statement: 1. It scares 2. It scares 3. It scares 4. It scares 0 very little
me me me me
when when when when 1 a little
I feel shaky. I feel faint. my heart beats rapidly. I become short of breath. 2 SOIlIt?
3 much
4 very much
76
W. 1. APFELDORFET AL.
FIG. 1. ROC CURVEFORTHE BPDS IN THECROSS-VALIDATION SAMPLE.
(complement of specificity) decreases, but so does the true positive rate (sensitivity). For example, a cutscore of 8 on BPDS in the cross-validation sample corresponds to sensitivity of 93% and specificity of 50%, whereas a cutscore of 11 on the BPDS corresponds to 78% sensitivity and 73% specificity in distinguishing panic disorder patients from those with other anxiety disorders, correctly classifying three-quarters of the subjects. DISCUSSION In our clinical sample of anxiety disordered subjects, panic disordered patients scored significantly higher on the AS1 than did the other anxiety disorder patients. This concurs with a smaller clinical sample reported by Taylor and coworkers (1992). Scores on the AS1 in our panic disorder sample are similar to published scores for agoraphobic patients (Reiss et al., 1986; McNally & Lorenz, 1987; Wardle, Ahmad, & Hayward, 1990) and higher than published scores on the AS1 in healthy and spider-phobic samples, which average around 18 (Wardle, Ahmad, & Hayward, 1990; Taylor et al, 1992). In addition, our study identified a new four-item Brief Panic Disorder Screen (BPDS) derived from the ASI. The BPDS appears to be as effective in discriminating panic disordered patients from other anxiety disordered patients. If the utility of this scale is confirmed in a general medical setting, for example, it would provide the clinician with a simple way of identifying patients likely to suffer from panic disorder, and would facilitate early detection and early implementation of appropriate treatment. Identification of a patient scoring 11 or above on the BPDS would trigger referral for a more complete diagnostic interview.
A
BRIEFSCREENFOR PANIC
DISORDER
77
In our sample a cutscore of 11 on the BPDS correctly discriminates Panic Disorder from other anxiety disorders in 75% of cases. Selection of a cutscore depends on the purpose for which the instrument is used. Further work in medical clinic populations is necessary to identify the optimal cutscore for use in that setting. However, in the interim, our cutscore could serve as a guideline for clinicians who implement the scale. The BPDS is a potentially useful self-rated scale, which would have uses both in and outside the psychiatric clinic. The scale may be applied in different patient care settings, as is currently done for alcohol abuse with the Michigan Alcohol Screening Test (Selzer, 1971) and CAGE (Mayfield, McLeod, & Hall, 1974). The sensitivity and specificity of an assessment instrument is ideally studied by administration to both well and ill samples (Johnstone & Goldberg, 1976). Administration of the BPDS in a medical clinic would accomplish this. An alternate technique, the one we used here, is to demonstrate the capacity of the instrument to detect cases shown previously to be responsive to treatment in controlled clinical trials (Meakin, 1992). Ideally, both would be done. The goal in developing the BPDS, as with other screening programs, is twofold. A screen proposes to serve as an economic and efficient means for detecting those individuals who will benefit from more complete assessment. However, it also serves to heighten awareness of a disorder among clinicians and the public. By alerting clinicians to the existence of Panic Disorder, the BPDS may help prevent needless distress, impairment, and cost from this public health problem.
REFERENCES Anthony, M. M., Brown, R. A., & Barlow, D. H. (1992). Current perspectives on panic and panic disorder. Current Directions in Psychological Sciences, 1.79-82. American Psychiatric Association (1987). Diagnostic and statistical manual of mental disorakrs (3rd edition, Revised) (DSM-III-R). Washington, DC: Author. Beck, A. T., Ward, C. H., Mendelson, M.. Mock, J. E., & Erbaugh, J. K. (1961). An inventory for measuring depression. Archives of General Psychiatry, 46,561-571. Clark, D. M. (1986). A cognitive approach to panic. Behaviour Research and Therapy, 24, 461-470.
Cohen, J. (.1992).A power primer. Psychological Bulletin, 112, 155-159. Cronbach, L. J. (1951). Coefficient alpha and the internal structure of tests. Psychometrika, 297-334. Donnell, C. D., & McNally, R. J. (1989). Anxiety sensitivity and history of panic as predictors of response to hyperventilation. Behaviour Research and Therapy, 27.325-332. Eaton, W. W., Dryman, R., & Weissman, M. M. (1991). Panic and phobia. In L. N. Robins & D. A. Regier (F&G.),Psychiatric disorders in America (pp. 155-179). New York: Free Press. Endicott, J., & Spitzer, R. L. (1978). A diagnostic interview: The schedule for affective disorders and schizophrenia. Archives of General Psychiatry, 35,837&W. Fleiss, J. L., & Shrout, P. E. (1989). Reliability considerations in planning diagnostic validity studies. In L. N. Robins & J. E. Barrett, (Eds.), The validity of psychiatric diagnosis (pp. 279-291). New York: Raven Press. Goldstein, A. J., & Chambless, D. L. (1978). A reanalysis of agoraphobia. Behavior Therapy, 9, 47-59.
Hoeper, E. W., Nycz, G. R., Cleary, P. D., Regier, D. A., & Goldberg, I. D. (1979). Estimated prevalence of RDC mental disorder in primary medical care. International Journal of Mental Health, 8,6-15.
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Hsiao, J. K., Barko, J. J., & Potter, W. Z. (1989) Diagnosing diagnoses: Receiver operating characteristic methods and psychiatry. Archives of General Psychiatry, 46,664&l. Johnstone, A., & Goldberg, D. (1976). Psychiatric screening in general practice: A controlled trial. Lancer, 605-608. Katon, W. (1984). Panic disorder and somatization: A review of 55 cases. American Journal of Medicine, 77,101-106.
Klerman, G. L., Weissman, M. M., Ouelette. R., Johnson. J., & Greenwald, S. (1991). Panic attacks in the community: Social morbidity and health care utilization. Journal of the American Medical Association, 265,742-146. Mailer, R. G., & Reiss, S. (1992). Anxiety sensitivity and panic attacks: A longitudiial analysis. Journal of Anxiety Disorders, 6.241-241.
Mayfield, D., McLeod, G., & Hall, P. (1974). The CAGE Questionnaire: Validation of a new alcoholii screening instrument. American Journal of Psychiatry, 131,1121-1123. McNally, R. J. (1990). Psychological approaches to Panic Disorder: A review. Psychological Bulletin, 108,403--119. Journal of Behavior Therapy and Experimental Therapeutics, 18, 3-l 1. Meakin, C. J. (1992) Screening for depression in the medically ill; ‘lhe future of paper and pencil tests. British Journal of Psychiatry, 160,212-216. NIH (1991). Treatment of Panic Disorder. National Institutes of Health Consensus Development Conference Consensus Statement, 9. Bethesda, MD: Author. Reiss, S. (1991) Expectancy model of fear, anxiety, and panic. Clinical Psychology Review, 11,
McNally, R. J., & Lorenz, M. (1987). Anxiety sensitivity in agoraphobics.
141-153. Reiss S., Peterson, R. A., Gursky, D. M., & McNally, R. J. (1986). Anxiety sensitivity, anxiety frequency, and the prediction of fearfulness. Behaviour Research and Therapy, 24, l-8. Seizer, M. (1971). The Michigan Alcoholism Screening Test: The quest for a new diagnostic instrument. American Journal of Psychiatry, 127.89-94. Skerrit, P. W. (1977). Anxiety and the heart-a historical review, 13, 17-25. Spitzer, R. L., Williams, J. B. W., Gibbon, M., & First, M. B. (1990). Structured Clinical Interviewfor DSM-III-R. Washington, DC American Psychiatric Press. Stewart, A. L., Hays, R. D., & Ware, Jr., J. E. (1988). The MOS short-form general health survey, 26,724-132. Taylor, S., Koch, W. J., & Crockett, D. J. (1991). Anxiety sensitivity, trait anxiety, and the anxiety disorders. Journal of Anxiety Disorders, 5.293-3 11. Taylor, S.. Koch, W. J., h McNally, R. J. (1992). How does anxiety sensitivity vary across the anxiety disorders? Journal of Anxiety Disorders, 6,249-259. Wardle, J., Ahmad, T., & Hayward, P. (1990). Anxiety sensitivity in agoraphobia. Journal of Anxiety Disorders, 4325-333.
Wiiliams, J. B. W., Gibbon, M., First, M. B., Spitzer, R. L., Davies, M., Borus, J., Howes, M. J., Kane, J., Pope, Jr., H. G., Rounsaville, B., & Wittchen, H.-U. (1992). The structured clinical interview for DSM-III-R @CID): II. Multisite test-retest reliability. Archives of General Psychiatry, 49.630-636. Wilson, J. M. G., & Jungner, F. (1968). Principles and practice of screening for disease. Public Health Papers No. 34. Geneva: World Health Organization.
Journal of AnxietyDisorders,Vol.8, No. 1,pp. 71-78, 1994 Copyright0 1994 Elsevier Science Ltd Printedin the USA. AU rights reserved 0887-6185194 $6.00 + .OO
A Brief Screen for Panic Disorder WILLIAM J. APFELDORF,M.D., PH.D., M. KATHERINESHEAR, M.D., ANDREW C. LEON, PH.D., ANDLAURA PORTERA,B.A. Department of Psychiatry, New York HospitaVCornell University Medical College
Abstract - Panic disorder is associated with excessive social morbidity and linancial burden. Delay in its diagnosis is a serious problem confronting the health care system. Screening instruments can be used to alert clinicians to the presence of an illness. In the current study, 143 patients presenting to an outpatient anxiety disorders clinic completed both self-report scales and a structured clinical interview. The 16-item Anxiety Sensitivity Index (ASI) selectively discriminates panic disorder subjects from subjects with other anxiety disorders in an anxiety clinic population. Further analyses demonstrate that a scale composed of merely four ASI items also discriminates panic disorder patients with equal sensitivity and specificity to the overall instrument. This new composite scale, named Brief Panic Disorder Screen (BPDS), will allow rapid identification of those patients who may benefit from more extensive evaluation for the presence of panic disorder.
Panic attacks are sudden and spontaneous discrete periods of intense fear and anxiety associated with shortness of breath, dizziness, palpitations, nausea, or abdominal distress. During an attack, people often believe they are losing control, having a heart attack, or losing their minds. At least four of these attacks must occur within a four-week period, or at least one of the attacks must be followed by a month of persistent fear of having another attack to meet DSM-IIIR diagnostic criteria for panic disorder (American Psychiatric Association, 1987). People with panic disorder frequently believe that they have a severe physical illness and seek medical attention (Katon, 1984). Physicians tend to describe anxiety symptoms from the viewpoint of their own specialty (Skerrit, 1977). For example, cardiologists focus on atypical chest pain, pulmonologists on hyperventilation, and gastroenterologists on irritable bowel symptoms when, in fact, these various symptoms are actually manifestations of a panic disorder. This results in underdiagnosis of panic disorder (Katon, 1984). Delays in proper diagnosis are costly both the individual and the health care delivery system. The average medical costs per patient in the first nine years after panic Dr. Shear is now with the Departmentof Psychiatry, University of Pittsburgh. Correspondence should be addressed to Dr. Apfeldorf, Payne Whitney Clinic, New York Hospital/CornellMedical Center,525 East 68th Street, New York,NY 10021. This research was supported in part by me Reader’s Digest Fund (WJA). 71
72
W. 1.
ET AL.
onset have estimated to greater than (Anthony, Brown, Barlow, 1992). and active could reduce the psychological and financial of panic A structured assessment performed a trained is the accurate way determine if patient meets for a diagnosis. such an is impractical use with patient in general medical More efficient methods are to identify that merit comprehensive evaluation. comprehensive would confirm who clearly diagnostic criteria who should referred for Some diseases particularly important identify by widespread screenstrategy. Three for such have been (Wilson & 1968). Panic appears to all of criteria. First, disease should an important health problem a sizable portion of population. The Catchment Area Program found the lifetime of panic is 1.5% the general ulation of adults (Eaton, & Weissman, Second, there be period which the is present, unrecognized. For subjects with disorder, several elapse during panic symptoms not recognized part of disorder, yet impairment (Anthony, Brown, Barlow, 1992). addition, the Survey found 28.4% of with panic visited emergency for their problem, and sought only general medical (Klerman, Weissman, Johnson, & 1991). Third, should exist may be once the is estabMedication and approaches effectively both the and the of panic (NIH, 1991). Panic Disorder a good for the of a program. Investigators used self-report (Stewart, Hays, Ware, 1988; Ward, Mendelson, & Erbaugh, and structured interviews (Endicott Spitzer, 1978; Williams, Gibbon, First, 1990) screen for disorders. Self-report are easy administer; however, often are diagnostically specific. interviews are specific, but time and makes their difficult and A more approach is two-stage case strategy in a self-report is used select highpatients on a structured is then (Fleiss & 1989; Hoeper, Cleary, Regier, Goldberg, 1979). Disorder patients prone to fearfulness of sensations, of those associated with (McNally, 1990; 1991). Such is postulated play an role in disorder, to the model of disorder (Goldstein Chambless, 1978; 1986). The Sensitivity Index an operationalized measure of of bodily (ASI: Reiss, Gursky, & 1986; McNally Lorenz, 1987). Koch, and (1992) reported the AS1 among the anxiety disorders. scores assowith each the six anxiety disorders, the exception
73
A BRIEFSCREENFORPANIC DISORDER
simple phobia, were greater than those of normal subjects. AS1 scores associated with Panic Disorder were significantly higher than those with other anxiety disorders, with the exception of Post-Traumatic Stress Disorder, where there was a trend for the Panic Disorder score to be higher. In contrast, the State-Trait Anxiety Index - Trait did not discriminate among anxiety disorders. These investigators concluded that the AS1 measures a construct distinct from that measured by the State-Trait Anxiety Index - Trait, and that the AS1 can be used to discriminate anxiety disorder diagnoses. Other studies support the importance of anxiety sensitivity in panic disorder. In a longitudinal study, high AS1 scores predicted frequency and intensity of panic attacks three years later (Maller & Reiss, 1992). In a provocation paradigm, subjects with high anxiety sensitivity scores demonstrated enhanced reactions to a hyperventilation challenge (Donnell & McNally, 1989). To explore further the usefulness of the AS1 as a screening instrument for panic disorder, we replicated the findings of Taylor, Koch, and Crockett (1991) demonstrating the specificity of the AS1 for panic disorder. We then undertook a two-step analytic procedure to attempt to identify a subscale of AS1 items that might be useful as a screen for panic disorder.
METHODS Subjects One hundred forty-three outpatients who presented to the Payne Whitney Clinic Anxiety Disorders Clinic and who were diagnosed by structured interview (SCID) as having a primary anxiety disorder were participants in the study. The characteristics of the subject sample are presented in Table 1.
TABLE 1 CLINIC bPULAllON
primary
Diagnosis
A. Panic Disorder Panic Disorder + Agoraphobia Panic Disorder - Agoraphobia Total Panic Disorder
&ARAClERIS?lCS
NUIllber
Female
Age (SD)
85 8
79% 75%
38.9 (12.1) 41.0 (13.4)
93
78%
39.1 (12.2)
B. Other Anxiety Disorders Agoraphobia Social Phobia Simple Phobia Generalized Anxiety Disorder Obsessive Compulsive Disorder Post-Traumatic Stress Disorder Anxiety Disorder NOS
4 18 20 0 0
Total Other Anxiety Disorders
50
100% 29% 50% 61% 50%
33.3 (8.6) 51.8 (13.9) 49.4 (13.8) 37.1 (11.3)
52%
42.3 (13.6)
46
14
W. J. APFELDORF IT AL.
The 143 patients included 99 women and 44 men. The mean age of the subjects was 40.2 f 12.6 years. Ninety-three met DSM-III-R criteria for Panic Disorder with or without Agoraphobia. Fifty met criteria for a different primary anxiety disorder. Gender and age characteristics of each diagnostic group are presented in Table 1. Procedure Patients contacting the Clinic were screened by phone interview to determine the likely presence of an anxiety disorder. Patient evaluation included a questionnaire packet containing self-report scales and participation in a structured clinical interview. Patients agreeing to complete the questionnaires and interview signed informed consents. Psychometric responses and diagnoses were collected independently. Assessments The Anxiety Sensitivity Index is a 16-item self-report measure of fear of anxiety (Reiss et al., 1986). Responses to each item are made on a five-point Likert scale from “very little” to “very much.” AS1 total score is calculated by summing the 16 items, resulting in a possible range of 0 to 64. Representative items include “it is important to me not to appear nervous,” “it scares me when I become short of breath,” and “unusual body sensations scare me.” High scores represent greater fear of bodily sensations. Diagnoses were established using the Structured Clinical Interview for DSM-III-R (SCID, Spitzer et al., 1990). conducted by a trained rater. Testretest reliability of the SCID for the current diagnosis of panic disorder has been reported as X = 0.58, respectively (Williams et al., 1992). Data Analyses The ability of the AS1 to discriminate patients who met criteria for panic disorder (with and without agoraphobia) from those with other anxiety disorders was evaluated. The AS1 total scores for the two groups were compared using t-tests. We conducted further analysis in order to explore the possibility that a subset of questions might be used to identify panic disorder subjects. A stratified randomization procedure was used to generate two groups of subjects: an “index” sample and a “cross-validation” sample. The stratification was based on dividing the study sample into two groups: panic disorder patients and other anxiety disorder patients. Subjects in each of these groups were randomly assigned to either the “index” sample or the “cross-validation” sample. A two-step procedure was then used to select a subset of items that could comprise a brief screen. To identify AS1 items that best differentiated between panic disorder and other anxiety disordered subjects, a between-group effect size (ES) was calculated for each AS1 item. The ES is defined by Cohen (1992) as the ratio of the difference between group means relative to the pooled standard deviation. This quantity reflects the magnitude of the differ-
75
A BREF SCREEN FOR PANIC DISORDER
ence between the two groups relative to variability within each group. It is equal to the absolute value of the difference between group means, divided by the pooled standard deviation, 1jT1 - Ti;,I/ Spooled. Items with ES 2 0.80 were identified and included in the subscale, based on the proposal of Cohen (1992) for a “large” ES in a between-group f-test. An unweighted sum of those items formed the Brief Panic Disorder Screen (BPDS). These item analyses were conducted using the index sample. The internal consistency among the BPDS items was examined using Cronbach’s coefficient a (Cronbach, 1951) on the pooled index and cross-validation samples. The cross-validation sample was then used to contruct receiver operator characteristic (ROC) curves. These curves were used to select an optimal cutscore on the BPDS for case identification (Hsiao, Barko, & Potter, 1989). The ROC curve was used to compare the tradeoff between sensitivity and specificity of the various cutscores. Subjects scoring at or above the respective cutscores are classified as “cases,” and the others as “non-cases.”
RESULTS The Panic Disorder group (n = 93) had a mean AS1 score of 38.4 f SD 11.6. This was signilicantly higher than the Other Anxiety Disorder group (n = 50) mean score of 27.6 + SD 12.3 (p c 0.001). The stratified randomization of the subjects groups yielded an index sample (n = 82) and a cross-validation sample (n = 63), each containing 65% Panic Disorder subjects. Four AS1 items had large between-group effect sizes (ES 2 0.8) in the index sample. These four items form the new scale, the Brief Panic Disorder Screen (BPDS), and are listed in Table 2. The minimum score possible on the resulting four-item BPDS is 0 and the maximum score possible is 16. In the cross-validation sample, the panic disorder group had a mean score of 12.6 + SD 4.0. This is significantly higher than the other anxiety disorder group, which had a mean score of 7.5 + SD 4.1 (p < 0.001). Cronbach’s coefficient c1 for the BPDS is 0.875, indicating a high degree of consistency among the four items. The ROC curve for the new scale in the cross-validation sample is presented in Fig. 1. Note that as the cutscore increases, the false positive rate TABLE 2 BRIEFPANIC DISORDERSCALE
Please. rate each item by circling one of the five phrases for each statement: 1. It scares 2. It scares 3. It scares 4. It scares 0 very little
me me me me
when when when when 1 a little
I feel shaky. I feel faint. my heart beats rapidly. I become short of breath. 2 SOIlIt?
3 much
4 very much
76
W. 1. APFELDORFET AL.
FIG. 1. ROC CURVEFORTHE BPDS IN THECROSS-VALIDATION SAMPLE.
(complement of specificity) decreases, but so does the true positive rate (sensitivity). For example, a cutscore of 8 on BPDS in the cross-validation sample corresponds to sensitivity of 93% and specificity of 50%, whereas a cutscore of 11 on the BPDS corresponds to 78% sensitivity and 73% specificity in distinguishing panic disorder patients from those with other anxiety disorders, correctly classifying three-quarters of the subjects. DISCUSSION In our clinical sample of anxiety disordered subjects, panic disordered patients scored significantly higher on the AS1 than did the other anxiety disorder patients. This concurs with a smaller clinical sample reported by Taylor and coworkers (1992). Scores on the AS1 in our panic disorder sample are similar to published scores for agoraphobic patients (Reiss et al., 1986; McNally & Lorenz, 1987; Wardle, Ahmad, & Hayward, 1990) and higher than published scores on the AS1 in healthy and spider-phobic samples, which average around 18 (Wardle, Ahmad, & Hayward, 1990; Taylor et al, 1992). In addition, our study identified a new four-item Brief Panic Disorder Screen (BPDS) derived from the ASI. The BPDS appears to be as effective in discriminating panic disordered patients from other anxiety disordered patients. If the utility of this scale is confirmed in a general medical setting, for example, it would provide the clinician with a simple way of identifying patients likely to suffer from panic disorder, and would facilitate early detection and early implementation of appropriate treatment. Identification of a patient scoring 11 or above on the BPDS would trigger referral for a more complete diagnostic interview.
A
BRIEFSCREENFOR PANIC
DISORDER
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In our sample a cutscore of 11 on the BPDS correctly discriminates Panic Disorder from other anxiety disorders in 75% of cases. Selection of a cutscore depends on the purpose for which the instrument is used. Further work in medical clinic populations is necessary to identify the optimal cutscore for use in that setting. However, in the interim, our cutscore could serve as a guideline for clinicians who implement the scale. The BPDS is a potentially useful self-rated scale, which would have uses both in and outside the psychiatric clinic. The scale may be applied in different patient care settings, as is currently done for alcohol abuse with the Michigan Alcohol Screening Test (Selzer, 1971) and CAGE (Mayfield, McLeod, & Hall, 1974). The sensitivity and specificity of an assessment instrument is ideally studied by administration to both well and ill samples (Johnstone & Goldberg, 1976). Administration of the BPDS in a medical clinic would accomplish this. An alternate technique, the one we used here, is to demonstrate the capacity of the instrument to detect cases shown previously to be responsive to treatment in controlled clinical trials (Meakin, 1992). Ideally, both would be done. The goal in developing the BPDS, as with other screening programs, is twofold. A screen proposes to serve as an economic and efficient means for detecting those individuals who will benefit from more complete assessment. However, it also serves to heighten awareness of a disorder among clinicians and the public. By alerting clinicians to the existence of Panic Disorder, the BPDS may help prevent needless distress, impairment, and cost from this public health problem.
REFERENCES Anthony, M. M., Brown, R. A., & Barlow, D. H. (1992). Current perspectives on panic and panic disorder. Current Directions in Psychological Sciences, 1.79-82. American Psychiatric Association (1987). Diagnostic and statistical manual of mental disorakrs (3rd edition, Revised) (DSM-III-R). Washington, DC: Author. Beck, A. T., Ward, C. H., Mendelson, M.. Mock, J. E., & Erbaugh, J. K. (1961). An inventory for measuring depression. Archives of General Psychiatry, 46,561-571. Clark, D. M. (1986). A cognitive approach to panic. Behaviour Research and Therapy, 24, 461-470.
Cohen, J. (.1992).A power primer. Psychological Bulletin, 112, 155-159. Cronbach, L. J. (1951). Coefficient alpha and the internal structure of tests. Psychometrika, 297-334. Donnell, C. D., & McNally, R. J. (1989). Anxiety sensitivity and history of panic as predictors of response to hyperventilation. Behaviour Research and Therapy, 27.325-332. Eaton, W. W., Dryman, R., & Weissman, M. M. (1991). Panic and phobia. In L. N. Robins & D. A. Regier (F&G.),Psychiatric disorders in America (pp. 155-179). New York: Free Press. Endicott, J., & Spitzer, R. L. (1978). A diagnostic interview: The schedule for affective disorders and schizophrenia. Archives of General Psychiatry, 35,837&W. Fleiss, J. L., & Shrout, P. E. (1989). Reliability considerations in planning diagnostic validity studies. In L. N. Robins & J. E. Barrett, (Eds.), The validity of psychiatric diagnosis (pp. 279-291). New York: Raven Press. Goldstein, A. J., & Chambless, D. L. (1978). A reanalysis of agoraphobia. Behavior Therapy, 9, 47-59.
Hoeper, E. W., Nycz, G. R., Cleary, P. D., Regier, D. A., & Goldberg, I. D. (1979). Estimated prevalence of RDC mental disorder in primary medical care. International Journal of Mental Health, 8,6-15.
W. 1. APFELDORF ET AL.
78
Hsiao, J. K., Barko, J. J., & Potter, W. Z. (1989) Diagnosing diagnoses: Receiver operating characteristic methods and psychiatry. Archives of General Psychiatry, 46,664&l. Johnstone, A., & Goldberg, D. (1976). Psychiatric screening in general practice: A controlled trial. Lancer, 605-608. Katon, W. (1984). Panic disorder and somatization: A review of 55 cases. American Journal of Medicine, 77,101-106.
Klerman, G. L., Weissman, M. M., Ouelette. R., Johnson. J., & Greenwald, S. (1991). Panic attacks in the community: Social morbidity and health care utilization. Journal of the American Medical Association, 265,742-146. Mailer, R. G., & Reiss, S. (1992). Anxiety sensitivity and panic attacks: A longitudiial analysis. Journal of Anxiety Disorders, 6.241-241.
Mayfield, D., McLeod, G., & Hall, P. (1974). The CAGE Questionnaire: Validation of a new alcoholii screening instrument. American Journal of Psychiatry, 131,1121-1123. McNally, R. J. (1990). Psychological approaches to Panic Disorder: A review. Psychological Bulletin, 108,403--119. Journal of Behavior Therapy and Experimental Therapeutics, 18, 3-l 1. Meakin, C. J. (1992) Screening for depression in the medically ill; ‘lhe future of paper and pencil tests. British Journal of Psychiatry, 160,212-216. NIH (1991). Treatment of Panic Disorder. National Institutes of Health Consensus Development Conference Consensus Statement, 9. Bethesda, MD: Author. Reiss, S. (1991) Expectancy model of fear, anxiety, and panic. Clinical Psychology Review, 11,
McNally, R. J., & Lorenz, M. (1987). Anxiety sensitivity in agoraphobics.
141-153. Reiss S., Peterson, R. A., Gursky, D. M., & McNally, R. J. (1986). Anxiety sensitivity, anxiety frequency, and the prediction of fearfulness. Behaviour Research and Therapy, 24, l-8. Seizer, M. (1971). The Michigan Alcoholism Screening Test: The quest for a new diagnostic instrument. American Journal of Psychiatry, 127.89-94. Skerrit, P. W. (1977). Anxiety and the heart-a historical review, 13, 17-25. Spitzer, R. L., Williams, J. B. W., Gibbon, M., & First, M. B. (1990). Structured Clinical Interviewfor DSM-III-R. Washington, DC American Psychiatric Press. Stewart, A. L., Hays, R. D., & Ware, Jr., J. E. (1988). The MOS short-form general health survey, 26,724-132. Taylor, S., Koch, W. J., & Crockett, D. J. (1991). Anxiety sensitivity, trait anxiety, and the anxiety disorders. Journal of Anxiety Disorders, 5.293-3 11. Taylor, S.. Koch, W. J., h McNally, R. J. (1992). How does anxiety sensitivity vary across the anxiety disorders? Journal of Anxiety Disorders, 6,249-259. Wardle, J., Ahmad, T., & Hayward, P. (1990). Anxiety sensitivity in agoraphobia. Journal of Anxiety Disorders, 4325-333.
Wiiliams, J. B. W., Gibbon, M., First, M. B., Spitzer, R. L., Davies, M., Borus, J., Howes, M. J., Kane, J., Pope, Jr., H. G., Rounsaville, B., & Wittchen, H.-U. (1992). The structured clinical interview for DSM-III-R @CID): II. Multisite test-retest reliability. Archives of General Psychiatry, 49.630-636. Wilson, J. M. G., & Jungner, F. (1968). Principles and practice of screening for disease. Public Health Papers No. 34. Geneva: World Health Organization.