Behav. Rex. The-r. Vat. 30,No.4, pp.411-413, 1992 Printed in Great Britain. All rights reserved
US-7%7/~2 %5.00+0.00 Copyright 0
1992 Perpmon
Press Ltd
Self-monitoring of panic attacks and retrospective estimates of panic: discordant findings EDWIN DE BEURS,‘* ALFRED LANGE’ and RICHARD VAN DYCK' ‘Department of Clinical Psychology, University of Amsterdam, Roetersstraat 15, 1018 WB, Amsterdam, The Netherlands andZDepartment of Psychiatry, Free University, De Boeielaan 1105, 1081 HY, Amsterdam, The Netherian& (Received 2 October
1991)
Summary-An event sampling method was used to study the frequency of panic attacks during treatment of agoraphobics. Results revealed a much lower incidence of panic attacks in agoraphobics according to self-monitoring than was expected on account of their retrospective estimation. When more stringent criteria for panic attacks are applied, retrospective overestimation becomes even more apparent. The implication of this finding for the classification of panic disorder patients is discussed.
INTRODUCTION Given the central role of panic attacks in the diagnosis of panic disorder (with or without agoraphobia), an adequate measurement of panic attacks is essential. Usually panic frequency is assessed by simply asking patients to estimate the number of panic attacks experienced during the last week or month. This method is applied in diagnostic interviews such as the Anxiety Disorders Interview Schedule--Revised (AD&R, DiNardo, O’Brien, Barlow, Waddell & Blanchard, 1983) and in self-report questionnaires such as the panic frequency scale of the Mobility Inventory (MI-PF) (Chambless, Caputo, Jasin, Gracely 8r Williams, 1985). The reliability of these assessment techniques is obviously impaired by their retrospective character. At best a rough estimate of the actual frequency of attacks is provided (Tellegen, 1985). Still, also in pharmacotherapeutical research, retrospective recall as a method of assessment is commonly used (Klein & Klein, 1989; Klein, Ross & Cohen, 1987; Nagy, Krystal, Woods & Charney, 1989). In recent years, more sophisticated methods of assessing panic have become available, particularly with the development of continuous self-monitoring of panic (Michelson, 1987; Walker, Norton & Ross, 1991). In this continuous monitoring method the patient keeps a diary in which every panic attack is jotted down immediately after the attack occurs (e.g. Margraf, Taylor, Ehlers, Roth & Agras, 1987; Klosko, Barlow, Tassinari & Cerny, 1990). In current research on panic patients, daily monitoring of panic attacks has become a frequently used procedure. In the present study, panic frequency was assessed during treatment by continuous self-monitoring. In addition, the same patients were repeatedly asked to give a retrospective estimation of the frequency of panic. Results of the two methods of assessment are compared. This study was part of a larger project, during which exposure in viva and cognitive behavioural treatment for panic attacks was given. Results of this treatment will not be reported in this article.
METHOD
Assessment
of panic attacks
A panic attack was defined as a sudden outburst of intense fear with the following characteristics: (1) a high level of anxiety, accompanied by (2) strong bodily reactions such as heart palpitations, sweating, etc. Additional characteristics to describe the event (but not a prerequisite) were: (3) a temporary loss of the ability to plan, think, or reason and (4) the intense desire to escape or flee the situation. This rather lenient definition of a panic attack as used by Chambless et al. (1985) was chosen to minimise the risk of the patient not reporting the occurrence of an attack, when in fact one had occurred. During the study, the patients were provided weekly with an adequate supply of forms on which the 13 symptoms of panic attack, as defined in the DSM-III-R (American Psychiatric Association, 1987), were listed. On a 5-point scale the patient could indicate to what extent (not at all to very much) these symptoms were present during the attack. This enabled the differentiation between panic attacks meeting the DSM-III-R criterion of at least four symptoms present or not (‘major’ attacks vs. ‘minor’ attacks, cf. Klein, 1981). On the back of each registration form, the above described definition of a panic attack was written as a memory support. Monitoring started in the week preceding the first treatment session. This first weak of monito~ng was considered to be a training period. In the first treatment session the results of the monito~ng were discussed with the patient to ensure that the registration was based on a correct definition of a panic attack. Results indicated that some patients initially found it difficult to discriminate between panic attacks and intense anxiety due to having a ‘bad day’. Therefore, special care was taken to point out the difference between anticipatory or long-lasting phobic anxiety and a panic attack by stressing the importance of the sudden outburst of fear, characteristic of the latter (cf. Klein & Klein, 1989). One question in the Mobility Inventory (MI; Chambless et al., 1985) pertains to panic frequency (MI-PF). This item is based on the same definition of a panic attack as described above. Patients are asked to indicate the total number of attacks experienced during the past 7 days. The MI was completed 1 week before the treatment started, halfway during the treatment and after the treatment. *Author for correspondence. 411
412
CASE HISTORIES
AND
SHORTER
COMMUNICATIONS
Table I. Mean panic frequency during treatment according to daily monitoring and according to retrosaective estimation of the oat&t Monitoring Major attacks Mean Week Week Week Week Week Week Week Week Week Week Week
I 2 3 4 5 6 7 8 9 IO 11
Week 12
0.73
1.03 1.01 0.83 0.88 I .06 0.60 0.45 0.65 0.54 0.59 0.35
All attacks Mean
SD
I .33 1.34 1.69 1.46 1.58
1.70
0.83 0.86 I .04 0.95 0.89 0.71
0.97 1.25 1.10 0.99 0.95 1.19 0.64 0.54 0.72 0.56 0.71 0.46
MI-PF
SD 1.49 1.79 1.67 1.78 1.64 1.93 0.83 0.87 1.16 0.96 0.94 0.78
Mean
SD
Pretest
1.93
2.40
Midtest
0.86
2.12
Posttest
0.46
0.74
Subjects (DSM-III-R; American Psychiatric Association, All patients met the criteria for ‘Panic Disorder with Agoraphobia’ 1987). Diagnoses were made by an experienced psychiatrist using the Anxiety Disorders Interview Schedule-Revised (ADIS-R; DiNardo et al., 1983; Dutch version: De Ruiter, Garssen, Rijken & Kraaimaat, 1987). Other relevant inclusion criteria were: a minimum duration of the agoraphobic avoidance of 6 months and a minimum score of 17 on the agoraphobia subscale of the Fear Questionnaire (Marks & Mathews, 1979).
RESULTS Thirty-two patients monitored panic attacks during the study. Two patients did not experience any attacks during this period, thus they were omitted from further analysis. Two additional patients experienced panic with such frequency, that they accounted for 24 and 13% respectively of all attacks monitored. Although their panic profile was exactly in line with the prediction of a linear decrease, the extreme frequency of panic of these two patients would bear too much weight on the mean frequency of the entire group. Therefore, they were excluded from the present analysis as well. The DSM-III-R definition of a panic attack is more stringent than the definition utilized in this study. According to the DSM-III-R at least four symptoms out of a list of thirteen should be present for an attack to be considered ‘full blown’ or ‘major’. Attacks not meeting this criterion are called ‘minor’ attacks. In the presentation of results we present the total number of attacks monitored as well as the number of attacks meeting the DSM-III-R criterion. The mean number of panic attacks according to the continuous monitoring method are presented in Table 1 together with the pretest, midtest and posttest means of the retrospective estimation of the patients (MI-PF). The pretest took place 1 week before the treatment started. It should be noted that therefore, the estimation pertained to the period 1 week before the monitoring commenced. The posttest was administered in the week after treatment. Therefore, the MI-PF-post pertained to the week following the last week of monitoring. In the initial phase of treatment, the frequency of panic attacks according to the monitoring method is much lower than the figure the MI-PF yields. The difference becomes even more apparent when the definition of a panic attack is narrowed down to the DSM-III-criterion for a major attack. Comparison of both means of assessment halfway yields a difference as well, but then the frequency of panic according to the monitoring method slightly outnumbers the MI-PF. At the end of treatment the frequency of panic according to monitoring and to the MI-PF match perfectly. The data of both methods of assessment of panic attacks are used to test the effect of the treatment on frequency of panic attacks. Treatment effect is tested by analysis of variance for repeated measurements, whereby a linear decrease of frequency was predicted (planned comparison; cf. Winer, 1971). The results are presented in Table 2. All tests indicated that there was a significant decrease of panic during the treatment, with the most significant decrease according to the MI-PF data. Since patients, when filling in the MI-PF, initially tend to overestimate the frequency of panic, this consequently yields an overestimation of the treatment effect. DISCUSSION
Retrospective estimation results in a substantial overrating of panic frequency compared to an event sampling approach. At pretest this overrating amounted to almost 100%. This result is in line with findings of Margraf et al. (1987), indicating that patients are inclined to overestimate both panic frequency and the severity of the panic attacks, when asked to give a retrospective account. As a consequence, treatment appeared far more effective in diminishing panic, when using the Table 2. Treatment effect according to analyses of variance of monitoring data and the MI-PF Monitoring
Treatment effect
Major attacks
All attacks
MI-PF
F = 1.85 d.f. = 11 P = 0.045
F= 1.78 d.f. = 1I P = 0.058
F = 7.05 d.f. = 2 P = 0.002
CASE HISTORIES AND SHORTER COMMUNICATIONS
413
MI-PF as assessment measure, than is actually the case. When concurrently monitoring their attacks, patients are likely to base their estimation on their own monitoring, which results in more concordance between both assessment methods. Furthermore, when a more precise assessment method is utilized, panic attacks seem to be less common to agoraphobia than is often assumed. This has consequences for the classification of anxiety disorders. Patients meeting the DSM-III-R criterion of four panic attacks in a 4-week period, may not actually suffer that number of attacks, when the frequency of attacks is accurately assessed. In panic research various subtypes of panic are discerned, mainly aimed at discriminating between extreme levels of phobic anxiety (also called situationally bound panic) and spontaneous panic. According to the definition of panic disorder in the DSM-III-R only a non-phobic panic attack should be considered a genuine panic attack (cf. Klein & Klein, 1989). In practice, it is often difficult to decide whether a panic attack is a response to exposure to a phobic situation or appeared ‘out of the blue’. We collected information on the spontaneous nature of each attack. Detailed findings are reported elsewhere (Garssen, De Beurs, Buikhuisen, Van Dyck & Lange, 1992). For the results here it is relevant to mention that about half of the attacks were expected by the patient or took place in a situation they experienced usually as threatening. Leaving these attacks out would further diminish the number of panic attacks experienced weekly. In that case an even smaller subset of our patients would still meet the criteria for panic disorder. REFERENCES
American Psychiatric Association (1987) Diagnostic and sfatistical manual of mental disorders (3rd Edn, rev.) (DSM-III R). Washington D.C.: American Psychiatric Association. Chambless, D. L., Caputo, G. C., Jasin, S. E., Gracely, E. J. &Williams, C. (1985). The Mobility Inventory for agoraphobia. Behaviour Research and Therapy, 23, 35-44. De Ruiter, C., Garssen, B., Rijken, H. & Kraaimaat, F. (1987). Anxiety Disorders Interview Schedule-Revised: Dutch translation. The Netherlands: Department of Psychiatry, University of Utrecht. DiNardo, P. A., O’Brien, G. T., Barlow, D. H., Waddell, M. T. & Blanchard, E. B. (1983). Reliability of DSM-III anxiety disorder categories using a new structured interview. Archives of General Psychiatry, 40, 1070-1075. Garssen, B., De Beurs, E., Buikhuisen, M., Van Dyck, R. & Lange, A. (1992). On distinguishing types of panic. Manuscript submitted for publication. Klein, D. F. (1981). Anxiety reconceptualized. In Klein, D. F. & Rabkin, J. G. (Eds), Anxiety: New research and changing concepts (pp. 325-365). New York: Raven Press. Klein, D. F. & Klein, H. M. (1989). The substantive effect of variations in panic measurement and agoraphobic definition. Journal of Anxiety Disorders, 3, 45-56. Klein, D. F., Ross, C. R. & Cohen, P. (1987). Panic and avoidance in agoraphobia. Archives of General Psychiatry, 44, 377-385. Klosko, J. S., Barlow, D. H., Tassinari, R. & Cerny, J. A. (1990). A comparison of alprazolam and behavior therapy in treatment of panic disorder. Journal of Consulting and Clinical Psychology, 58, 77-84. Margraf, J., Taylor, C. B., Ehlers, A., Roth, W. T. & Agras, W. S. (1987). Panic attacks in the natural environment. Journal of Nervous and Mental Disease, 175, 558-565. Marks, I. M. & Mathews, A. M. (1979). Brief standard self-rating for phobic patients. Behauiour Research and Therapy, 17, 263-267. Michelson, L. (1987). Cognitive-behavioral assessment and treatment of agoraphobia (pp. 213-279). In Michelson, L. & Ascher, L. M. (Eds), Anxiery and stress disorders: Cognitive-behavioral assessment and treatment. New York: Oxford Press. Nagy, L. M., Krystal, J. H., Woods, S. W. & Charney, D. S. (1989). Clinical and medication outcome after short-term alprazolam and behavioral group treatment in panic disorder. Archiues of General Psychiatry, 46, 993-999. Tellegen, A. (1985). Structures of mood and personality and their relevance to assessing anxiety, with an emphasis on self-report. Hillsdale, N.J.: Erlbaum. Walker, J. R., Norton, G. N. & Ross, C. A. (1991). Panic disorder and agoraphobia: A comprehensive guide to the practitioner. Pacific Grove, Calif.: Brooks/Cole. Winer, B. J. (1971). Statistical principles in experimental design. (2nd Ed.). Tokyo: McGraw-Hill.
US-7%7/~2 %5.00+0.00 Copyright 0
1992 Perpmon
Press Ltd
Self-monitoring of panic attacks and retrospective estimates of panic: discordant findings EDWIN DE BEURS,‘* ALFRED LANGE’ and RICHARD VAN DYCK' ‘Department of Clinical Psychology, University of Amsterdam, Roetersstraat 15, 1018 WB, Amsterdam, The Netherlands andZDepartment of Psychiatry, Free University, De Boeielaan 1105, 1081 HY, Amsterdam, The Netherian& (Received 2 October
1991)
Summary-An event sampling method was used to study the frequency of panic attacks during treatment of agoraphobics. Results revealed a much lower incidence of panic attacks in agoraphobics according to self-monitoring than was expected on account of their retrospective estimation. When more stringent criteria for panic attacks are applied, retrospective overestimation becomes even more apparent. The implication of this finding for the classification of panic disorder patients is discussed.
INTRODUCTION Given the central role of panic attacks in the diagnosis of panic disorder (with or without agoraphobia), an adequate measurement of panic attacks is essential. Usually panic frequency is assessed by simply asking patients to estimate the number of panic attacks experienced during the last week or month. This method is applied in diagnostic interviews such as the Anxiety Disorders Interview Schedule--Revised (AD&R, DiNardo, O’Brien, Barlow, Waddell & Blanchard, 1983) and in self-report questionnaires such as the panic frequency scale of the Mobility Inventory (MI-PF) (Chambless, Caputo, Jasin, Gracely 8r Williams, 1985). The reliability of these assessment techniques is obviously impaired by their retrospective character. At best a rough estimate of the actual frequency of attacks is provided (Tellegen, 1985). Still, also in pharmacotherapeutical research, retrospective recall as a method of assessment is commonly used (Klein & Klein, 1989; Klein, Ross & Cohen, 1987; Nagy, Krystal, Woods & Charney, 1989). In recent years, more sophisticated methods of assessing panic have become available, particularly with the development of continuous self-monitoring of panic (Michelson, 1987; Walker, Norton & Ross, 1991). In this continuous monitoring method the patient keeps a diary in which every panic attack is jotted down immediately after the attack occurs (e.g. Margraf, Taylor, Ehlers, Roth & Agras, 1987; Klosko, Barlow, Tassinari & Cerny, 1990). In current research on panic patients, daily monitoring of panic attacks has become a frequently used procedure. In the present study, panic frequency was assessed during treatment by continuous self-monitoring. In addition, the same patients were repeatedly asked to give a retrospective estimation of the frequency of panic. Results of the two methods of assessment are compared. This study was part of a larger project, during which exposure in viva and cognitive behavioural treatment for panic attacks was given. Results of this treatment will not be reported in this article.
METHOD
Assessment
of panic attacks
A panic attack was defined as a sudden outburst of intense fear with the following characteristics: (1) a high level of anxiety, accompanied by (2) strong bodily reactions such as heart palpitations, sweating, etc. Additional characteristics to describe the event (but not a prerequisite) were: (3) a temporary loss of the ability to plan, think, or reason and (4) the intense desire to escape or flee the situation. This rather lenient definition of a panic attack as used by Chambless et al. (1985) was chosen to minimise the risk of the patient not reporting the occurrence of an attack, when in fact one had occurred. During the study, the patients were provided weekly with an adequate supply of forms on which the 13 symptoms of panic attack, as defined in the DSM-III-R (American Psychiatric Association, 1987), were listed. On a 5-point scale the patient could indicate to what extent (not at all to very much) these symptoms were present during the attack. This enabled the differentiation between panic attacks meeting the DSM-III-R criterion of at least four symptoms present or not (‘major’ attacks vs. ‘minor’ attacks, cf. Klein, 1981). On the back of each registration form, the above described definition of a panic attack was written as a memory support. Monitoring started in the week preceding the first treatment session. This first weak of monito~ng was considered to be a training period. In the first treatment session the results of the monito~ng were discussed with the patient to ensure that the registration was based on a correct definition of a panic attack. Results indicated that some patients initially found it difficult to discriminate between panic attacks and intense anxiety due to having a ‘bad day’. Therefore, special care was taken to point out the difference between anticipatory or long-lasting phobic anxiety and a panic attack by stressing the importance of the sudden outburst of fear, characteristic of the latter (cf. Klein & Klein, 1989). One question in the Mobility Inventory (MI; Chambless et al., 1985) pertains to panic frequency (MI-PF). This item is based on the same definition of a panic attack as described above. Patients are asked to indicate the total number of attacks experienced during the past 7 days. The MI was completed 1 week before the treatment started, halfway during the treatment and after the treatment. *Author for correspondence. 411
412
CASE HISTORIES
AND
SHORTER
COMMUNICATIONS
Table I. Mean panic frequency during treatment according to daily monitoring and according to retrosaective estimation of the oat&t Monitoring Major attacks Mean Week Week Week Week Week Week Week Week Week Week Week
I 2 3 4 5 6 7 8 9 IO 11
Week 12
0.73
1.03 1.01 0.83 0.88 I .06 0.60 0.45 0.65 0.54 0.59 0.35
All attacks Mean
SD
I .33 1.34 1.69 1.46 1.58
1.70
0.83 0.86 I .04 0.95 0.89 0.71
0.97 1.25 1.10 0.99 0.95 1.19 0.64 0.54 0.72 0.56 0.71 0.46
MI-PF
SD 1.49 1.79 1.67 1.78 1.64 1.93 0.83 0.87 1.16 0.96 0.94 0.78
Mean
SD
Pretest
1.93
2.40
Midtest
0.86
2.12
Posttest
0.46
0.74
Subjects (DSM-III-R; American Psychiatric Association, All patients met the criteria for ‘Panic Disorder with Agoraphobia’ 1987). Diagnoses were made by an experienced psychiatrist using the Anxiety Disorders Interview Schedule-Revised (ADIS-R; DiNardo et al., 1983; Dutch version: De Ruiter, Garssen, Rijken & Kraaimaat, 1987). Other relevant inclusion criteria were: a minimum duration of the agoraphobic avoidance of 6 months and a minimum score of 17 on the agoraphobia subscale of the Fear Questionnaire (Marks & Mathews, 1979).
RESULTS Thirty-two patients monitored panic attacks during the study. Two patients did not experience any attacks during this period, thus they were omitted from further analysis. Two additional patients experienced panic with such frequency, that they accounted for 24 and 13% respectively of all attacks monitored. Although their panic profile was exactly in line with the prediction of a linear decrease, the extreme frequency of panic of these two patients would bear too much weight on the mean frequency of the entire group. Therefore, they were excluded from the present analysis as well. The DSM-III-R definition of a panic attack is more stringent than the definition utilized in this study. According to the DSM-III-R at least four symptoms out of a list of thirteen should be present for an attack to be considered ‘full blown’ or ‘major’. Attacks not meeting this criterion are called ‘minor’ attacks. In the presentation of results we present the total number of attacks monitored as well as the number of attacks meeting the DSM-III-R criterion. The mean number of panic attacks according to the continuous monitoring method are presented in Table 1 together with the pretest, midtest and posttest means of the retrospective estimation of the patients (MI-PF). The pretest took place 1 week before the treatment started. It should be noted that therefore, the estimation pertained to the period 1 week before the monitoring commenced. The posttest was administered in the week after treatment. Therefore, the MI-PF-post pertained to the week following the last week of monitoring. In the initial phase of treatment, the frequency of panic attacks according to the monitoring method is much lower than the figure the MI-PF yields. The difference becomes even more apparent when the definition of a panic attack is narrowed down to the DSM-III-criterion for a major attack. Comparison of both means of assessment halfway yields a difference as well, but then the frequency of panic according to the monitoring method slightly outnumbers the MI-PF. At the end of treatment the frequency of panic according to monitoring and to the MI-PF match perfectly. The data of both methods of assessment of panic attacks are used to test the effect of the treatment on frequency of panic attacks. Treatment effect is tested by analysis of variance for repeated measurements, whereby a linear decrease of frequency was predicted (planned comparison; cf. Winer, 1971). The results are presented in Table 2. All tests indicated that there was a significant decrease of panic during the treatment, with the most significant decrease according to the MI-PF data. Since patients, when filling in the MI-PF, initially tend to overestimate the frequency of panic, this consequently yields an overestimation of the treatment effect. DISCUSSION
Retrospective estimation results in a substantial overrating of panic frequency compared to an event sampling approach. At pretest this overrating amounted to almost 100%. This result is in line with findings of Margraf et al. (1987), indicating that patients are inclined to overestimate both panic frequency and the severity of the panic attacks, when asked to give a retrospective account. As a consequence, treatment appeared far more effective in diminishing panic, when using the Table 2. Treatment effect according to analyses of variance of monitoring data and the MI-PF Monitoring
Treatment effect
Major attacks
All attacks
MI-PF
F = 1.85 d.f. = 11 P = 0.045
F= 1.78 d.f. = 1I P = 0.058
F = 7.05 d.f. = 2 P = 0.002
CASE HISTORIES AND SHORTER COMMUNICATIONS
413
MI-PF as assessment measure, than is actually the case. When concurrently monitoring their attacks, patients are likely to base their estimation on their own monitoring, which results in more concordance between both assessment methods. Furthermore, when a more precise assessment method is utilized, panic attacks seem to be less common to agoraphobia than is often assumed. This has consequences for the classification of anxiety disorders. Patients meeting the DSM-III-R criterion of four panic attacks in a 4-week period, may not actually suffer that number of attacks, when the frequency of attacks is accurately assessed. In panic research various subtypes of panic are discerned, mainly aimed at discriminating between extreme levels of phobic anxiety (also called situationally bound panic) and spontaneous panic. According to the definition of panic disorder in the DSM-III-R only a non-phobic panic attack should be considered a genuine panic attack (cf. Klein & Klein, 1989). In practice, it is often difficult to decide whether a panic attack is a response to exposure to a phobic situation or appeared ‘out of the blue’. We collected information on the spontaneous nature of each attack. Detailed findings are reported elsewhere (Garssen, De Beurs, Buikhuisen, Van Dyck & Lange, 1992). For the results here it is relevant to mention that about half of the attacks were expected by the patient or took place in a situation they experienced usually as threatening. Leaving these attacks out would further diminish the number of panic attacks experienced weekly. In that case an even smaller subset of our patients would still meet the criteria for panic disorder. REFERENCES
American Psychiatric Association (1987) Diagnostic and sfatistical manual of mental disorders (3rd Edn, rev.) (DSM-III R). Washington D.C.: American Psychiatric Association. Chambless, D. L., Caputo, G. C., Jasin, S. E., Gracely, E. J. &Williams, C. (1985). The Mobility Inventory for agoraphobia. Behaviour Research and Therapy, 23, 35-44. De Ruiter, C., Garssen, B., Rijken, H. & Kraaimaat, F. (1987). Anxiety Disorders Interview Schedule-Revised: Dutch translation. The Netherlands: Department of Psychiatry, University of Utrecht. DiNardo, P. A., O’Brien, G. T., Barlow, D. H., Waddell, M. T. & Blanchard, E. B. (1983). Reliability of DSM-III anxiety disorder categories using a new structured interview. Archives of General Psychiatry, 40, 1070-1075. Garssen, B., De Beurs, E., Buikhuisen, M., Van Dyck, R. & Lange, A. (1992). On distinguishing types of panic. Manuscript submitted for publication. Klein, D. F. (1981). Anxiety reconceptualized. In Klein, D. F. & Rabkin, J. G. (Eds), Anxiety: New research and changing concepts (pp. 325-365). New York: Raven Press. Klein, D. F. & Klein, H. M. (1989). The substantive effect of variations in panic measurement and agoraphobic definition. Journal of Anxiety Disorders, 3, 45-56. Klein, D. F., Ross, C. R. & Cohen, P. (1987). Panic and avoidance in agoraphobia. Archives of General Psychiatry, 44, 377-385. Klosko, J. S., Barlow, D. H., Tassinari, R. & Cerny, J. A. (1990). A comparison of alprazolam and behavior therapy in treatment of panic disorder. Journal of Consulting and Clinical Psychology, 58, 77-84. Margraf, J., Taylor, C. B., Ehlers, A., Roth, W. T. & Agras, W. S. (1987). Panic attacks in the natural environment. Journal of Nervous and Mental Disease, 175, 558-565. Marks, I. M. & Mathews, A. M. (1979). Brief standard self-rating for phobic patients. Behauiour Research and Therapy, 17, 263-267. Michelson, L. (1987). Cognitive-behavioral assessment and treatment of agoraphobia (pp. 213-279). In Michelson, L. & Ascher, L. M. (Eds), Anxiery and stress disorders: Cognitive-behavioral assessment and treatment. New York: Oxford Press. Nagy, L. M., Krystal, J. H., Woods, S. W. & Charney, D. S. (1989). Clinical and medication outcome after short-term alprazolam and behavioral group treatment in panic disorder. Archiues of General Psychiatry, 46, 993-999. Tellegen, A. (1985). Structures of mood and personality and their relevance to assessing anxiety, with an emphasis on self-report. Hillsdale, N.J.: Erlbaum. Walker, J. R., Norton, G. N. & Ross, C. A. (1991). Panic disorder and agoraphobia: A comprehensive guide to the practitioner. Pacific Grove, Calif.: Brooks/Cole. Winer, B. J. (1971). Statistical principles in experimental design. (2nd Ed.). Tokyo: McGraw-Hill.
