Pergamon 0005-7967(94)00063-8

Behav. Res. Ther. Vol. 33, No. 3, pp. 243-258. 1995 Copyright ,i" 1995 Elsevier Science Ltd

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INVITED E S S A Y

A N X I E T Y S E N S I T I V I T Y : T H E O R E T I C A L P E R S P E C T I V E S

A N D R E C E N T F I N D I N G S

STEVEN TAYLOR Department of Psychiatry, 2255 Westbrook Mall, University of British Columbia, Vancouver,

B.C., Canada V6T 2AI

(Received 30 June 1994)

Summary--Anxiety sensitivity (AS) is the fear of anxiety-related sensations, which arises from beliefs that these sensations have harmful somatic, psychological or social consequences. According to Reiss (1991), AS is one of three fundamental fears that amplify or cause many common fears. AS also is thought to play an important role in causing panic attacks. The purpose of the present article is to review recent findings concerning the construct of AS and its place in the nomological network outlined by Reiss. Although the weight of evidence supports a unifactorial model of AS, recent findings suggest AS is multifactorial at the level of first-order factors, and these factors load on a single higher-order factor. People with elevated AS, compared to those with low AS, are more likely to have histories of panic attacks. AS is factorially distinct from other fundamental fears, and is more strongly related to agoraphobia than other common fears. AS can be regarded as a subfactor of trait anxiety, although the question arises as to whether AS is a cause of trait anxiety. Important questions for further investigation concern the etiology of AS and whether it can be reduced to still more basic fears.

Anxiety sensitivity (AS) is the fear of anxiety-related sensations, which arises from beliefs that these sensations have harmful somatic, psychological or social consequences (Reiss, 1987, 1991; Reiss & McNally, 1985). AS and related concepts have been proposed by several theorists over the past five decades [e.g. Fenichel (1945); Frankl (1959); see Reiss, (1987) for an historical review]. However, the theoretical and clinical significance of AS was recognized only recently, with the development of cognitive theories of fears, phobia and panic attacks. The purpose of the present article is to review recent studies of central issues and controversies about the conceptualization of AS and its place in the nomological network proposed by Reiss (1987, 1991; Reiss & McNally, 1985). To place the review in context, we first will examine the theoretical foundations of AS.

THEORETICAL PERSPECTIVES

Elevated AS is thought to play an important role in panic attacks and panic disorder. Clark (1986) proposed that panic attacks arise from the catastrophic misinterpretation of certain bodily sensations. To illustrate, if a physically healthy person misinterprets palpitations as an indication of an impending heart attacks, he/she is likely to become anxious. This will increase or prolong the palpitations which, in turn, will lead to further anxiety. Thus, a vicious cycle develops that culminates in a panic attacks. As the example shows, the vicious cycle is driven by the fear of anxiety-related bodily sensations. That is, the fear of sensations that are rapidly exacerbated by increases in arousal, such as cardiac or respiratory sensations. People prone to panic attacks are said to have an enduring tendency to become alarmed by those sensations (Clark, 1986, 1988). In other words, they have elevated AS.

Clark's (1986) theory can be subsumed within a broader theory of fears, phobia and panic developed by Reiss (1987, 1991; Reiss & McNally, 1985). According to Reiss, fear acquisition and exacerbation are a function of three fundamental fears (sensitivities): (1) Injury/illness sensitivity; (2) fear of negative evaluation; and (3) AS. Injury/illness sensitivity refers to fears of injury, illness

243

244 Steven Taylor

and death. Fear of negative evaluation is a concept developed by Watson and Friend (1969), and refers to apprehension and distress about being rejected or censured by others.

Reiss distinguished fundamental fears from common fears. Common fears are, for example, fears of harmless animals, fears of heights, fears of agoraphobic situations and social fears such as fears of writing or eating in public. Reiss (1991, and personal communication, June, 1991) used two criteria to define fears as fundamental. First, they are fears of stimuli that are inherently aversive for most people. Second, common fears can be logically reduced to fundamental fears: "Fundamental fears provide reasons for fearing a wide range of stimuli, whereas ordinary fears do not have this characteristic" (Reiss, 1991, p. 147).

It is not difficult to find examples where common fears appear to arise from fundamental fears. A person might be frightened of eating in public, not because eating is dangerous, but because of feared consequences such as choking on food (illness/injury sensitivity) or spilling one's food (fear of negative evaluation). Similarly, an agoraphobic might be frightened of shopping malls, not because malls are inherently dangerous, but because of fear of having a panic attack (AS). Fear of flying may arise from feared consequences such as the plane crashing (illness/injury sensitivity), fear of humiliating oneself by becoming air-sick (vomiting) during the flight (fear of negative evaluation), or fear of panicking while enclosed in the plane (AS). A person might be frightened of snakes for fear of being bitten (illness/injury sensitivity). Fear of snakes also would be amplified if the person is frightened about feeling anxious (AS) or worried about being ridiculed for having such an "irrational" fear (fear of negative evaluation). In summary, Reiss (1991) postulated that the fundamental fears amplify or exacerbate many common fears. In other words, common fears can be logically reduced to fundamental fears.

This logical reduction also may account for some rare and otherwise puzzling fears. To illustrate, Rachman and Seligman (1976) described the case of Mrs V., a patient admitted to hospital with a severe compulsive rituals arising from an intense fear of chocolate. She exhibited extreme fear when confronted with chocolate or any object or place associated with chocolate. She avoided most brown objects such as brown furniture and avoided shops that might sell chocolate. According to the patient and the independent report given by her husband, her fear of chocolate began shortly after the death of her mother, to whom she was very closely attached. Prior to her mother's death the patient enjoyed eating chocolate. Rachman and Seligman (1976) offered the following account of this unusual fear:

"It is barely possible that the fear of chocolate had as its origin a strong emotional reaction to the death of her mother during which time she had been obliged to observe the coffin containing the body. The patient believes that this coffin was dark brown in colour and that it may have contributed to the association which she had between death and chocolate. Even more telling, she feels sure that she saw a bar of chocolate in the room containing the coffin. This symbolic connection between death, the colour brown and chocolate might be based on too fanciful an interpretation but we did obtain confirmatory evidence of her fear of death scenes. During a behavioural avoidance test she displayed an inability to approach funeral parlours and considerable fear was aroused during the attempt" (p. 336).

In terms of Reiss' (1991) theory, Mrs V.'s intense fear of chocolate can be seen as arising from intense illness/injury sensitivity. This is consistent with Rachman and Seligman's (1976) conjecture that her fear of chocolate was a symbolic fear.

ISSUES AND C O N T R O V E R S I E S

Reiss' theory is an ambitious attempt at a comprehensive framework for understanding fears, phobia and panic attacks. The theory is still in its nascency. Some of its assumptions have been debated (e.g. Lilienfeld, in press; McNally, in press-a, in press-b), and empirical evaluation has begun only recently. The present article will review the literature to address five basic questions about the AS component of the theory:

1. Is AS.a unitary construct? 2. Is elevated AS associated with panic attacks? 3. Is AS distinct from other so-called fundamental fears? 4. How is AS related to common fears? 5. What is the relationship between AS and trait anxiety?

Anxiety sensitivity 245

IS ANXIETY SENSITIVITY A UNITARY CONSTRUCT?

Reiss (1991) assumed that AS is unidimensional, since it was proposed as one of the fundamental fears. Telch, Shermis and Lucas (1989a) argued that AS is multidimensional, with dimensions corresponding to different symptom domains, such as fears of cardiopulmonary symptoms, fears of gastrointestinal symptoms and so forth. If Telch et al. are correct then we will need to reformulate the concept of AS and modify Reiss's theory. In the following sections we review the factor analytic studies of AS scales.

A n x i e t y sensi t iv i ty index

One of the most widely used measures of AS is the Anxiety Sensitivity Index [ASI: Peterson & Reiss (1987)], which is a 16-item self-report inventory that assesses two aspects of AS: Beliefs about the dangerousness of anxiety sensations, and fears of those sensations. Subjects complete the ASI by rating the extent they agree with items such as "It scares me when I feel short of breath" and "When I notice that my heart is beating rapidly, I worry that I might have a heart attack." The ASI was constructed by Reiss, Peterson, Gursky and McNally (1986) to sample the content domain defined by Reiss' conception of AS. If the ASI adequately samples this domain, then evidence that the ASI is multifactorial would indicate that Reiss's theory is in need of modification.

There have been several exploratory factor analyses of the ASI using clinical and nonclinical samples. Three studies obtained single factor solutions (Reiss et al., 1986; Stewart, Dubois-Nguyen & Pihl, 1990; Taylor, Koch & Crockett, 1991), and three studies obtained four factors (Peterson & Heilbronner, 1987; Telch et al., 1989; Wardle, Ahmad & Hayward, 1990). The four factor solutions contained factors such as the following: Fears of cognitive and perceptual symptoms (e.g. dizziness, derealization), fears of cardiopulmonary sensations (e.g. palpitations, dyspnea), fears of gastrointestinal sensations (e.g. nausea), and fears of losing emotional or behavioral control (e.g. trembling). Each four-factor solution also contained one or more general factors, consisting of various combinations of these domains. Although there were some similarities among the four-factor solutions, there also were substantial differences. Indeed, Wardle et al. (1990) obtained markedly different four-factor solutons for agoraphobic and normal samples. The solution for the latter was described as having "little obvious psychological meaning" (p. 332). Peterson and Heilbronner (1987) obtained a four-factor solution but cautioned that it probably was unreliable because there were few salient loadings per factor. They concluded that the ASI is unifactorial.

The inconsistencies across studies may indicate the ASI factor structure is inherently unstable, or that its structure varies across populations. A simpler and more compelling explanation is that the inconsistencies arose from inappropriate methods of analysis. Each study, apart from those of Stewart et al. (1990) and Taylor et al. (1991) used Kaiser's "eigen values > 1" rule to determine the number of factors. Stimulation studies have shown that this rule tends to extract an excessive number of factors (Zwick & Velicer, 1986). Unreliability due to factor overextraction arises mainly at the stage of factor rotation, where the variance is redistributed from "true" factors to residual ("noise") factors. A more accurate extraction rule is the scree test (Zwick & Velicer, 1986). When this rule was used the ASI was found to be unifactorial in clinical and nonclinical samples (Taylor et al., 1991).

To further investigate the structure of AS, Taylor, Koch, McNally and Crockett (1992b) used confirmatory factor analysis to compare the single factor solution with the previously pub- lished four-factor solutions. Separate analyses were performed for patients with anxiety-related disorders, and spider-fearful university studies. Results were replicated across samples. In terms of goodness-of-fit, Telch et al. 's (1989a) solution was the best four-factor model. The degree of fit was little different from that of the single factor solution. Telch et al. 's solution was viable only when the factors were forced to orthogonality. When this constraint was removed, the factors were highly correlated, with rs up to 0.73. We concluded that "the oblique solution could be seen as part of a hierarchical factor structure in which all the oblique factors load on a superordinate factor. The oblique factors, however, are intercorrelated to such an extent that they are more appropriately regarded as facets of a single construct" (p. 250). It remains to be seen whether

246 Steven Taylor

an expanded version of the ASI yields a hierarchical model with factors that are not so highly correlated.

Agoraphobic cognitions questionnaire and body sensations questionnaire

The ASI contains items assessing the fear of bodily sensations and items assessing beliefs about the dangerousness of these sensations. The combination of cognitions and subjective fear within the same scale is consistent with the view that fears are composed of multiple components (Rachman, 1990). Chambless, Caputo, Bright and Gallagher (1984) developed two measures of AS with the aim of separating beliefs about anxiety sensations from fears of those sensations. The Body Sensations Question (BSQ) assesses the fear of 17 anxiety-related bodily sensations (e.g. nausea, palpitations, derealization). The Agoraphobic Cognitions Questionnaire (ACQ) requires the subject to rate how frequently they experience each of 14 thoughts when they are anxious. The ACQ contains two rationally derived subscales, assessing physical concerns (e.g. cardiac arrest) and social/behavioural concerns (e.g. losing control, acting foolishly).

There have been three publishing factor analytic studies of these scales. Chambless et al. (1984) administered the scales to 88 panic disordered patients. A two-factor solution was obtained for the ACQ, with factors corresponding to the rationally derived subscales. The factors were correlated 0.26. The BSQ was not factor analyzed, although it had high internal consistency (ct = 0.87), which suggests it was probably unifactorial.

Marks, Basoglu, Alkubaisy, Sengun and Marks (1991) administered the ACQ to 140 anxiety disordered patients. Three factors were extracted. The first corresponded to the physical concerns subscale, and the others split the subscale assessing social/behavioral concerns. There was no clear distinction between the latter factors; both assessed thoughts of losing control and acting in an embarrassing manner. The factors were extracted according to the eigen value > 1 rule, and so it may be that an excessive number of factors were extracted (Zwick & Velicer, 1986).

Arrindell (1993) reported exploratory and confirmatory factor analyses on responses from 94 patients with agoraphobia with or without panic disorder. Exploratory analyses were performed separately for the ACQ and BSQ. The ACQ was found to have two factors, corresponding to the rationally derived subscales. The BSQ was unifactorial. Arrindell factored the pool of ACQ and BSQ items with confirmatory factor analysis. It was hypothesized that three factors underlie the pool of items from the ACQ and BSQ; two corresponding to the ACQ subscales, and one corresponding to the BSQ. The model was found to have an adequate fit to the data. Alternative models were not examined.

It is not clear why Arrindell assumed the BSQ was factorially distinct from the ACQ. Theory (Clark, 1986) and research (e.g. Marks et al., 1991) suggests that subjective fears and cognitions are closely linked. That is, anxiety sensations are feared because the person believes them to be dangerous. Since Arrindell did not examine alternative models it is not known whether a model combining fears and cognitions would have provided a better fit than his 3-factor model. Thus, Arrindell's confirmatory factor sheds little light on the structure of AS.

The findings from the exploratory factor analyses of the ACQ may be taken as evidence that AS consists of two factors, corresponding to physical and social/behavioral concerns about the consequences of anxiety. This conclusion is inconsistent with the findings for the ASI, possibly because the latter have few items pertaining to social consequences of anxiety. The conclusion that AS is bifactorial is accepted only if one adopts a broad definition of this construct; a narrow definition indicates that AS is unifactorial. Reiss (1991) proposed that AS is the fear of anxiety sensations arising from beliefs that the sensations have harmful somatic, psychological or social consequences. Given this definition, AS appears to be bifactoriai. The problem with Reiss' (broad) definition of AS is that it blurs the distinction between AS and the fear of negative evaluation. That is, if anxiety sensations are feared because of anticipated social consequences (e.g. rejection or censure), then how is this different from fear of negative evalution?

A narrower definition of AS proposes that AS is the fear of anxiety sensations arising from beliefs that the sensations have harmful somatic or psychological consequences. This definition eliminates the overlap between AS and fear of negative evaluation. Given this definition, the ACQ factor assessing social/behavioral concerns corresponds largely to fear of negative evaluation, not to AS.

Anxiety sensitivity 247

The factor assessing physical concerns corresponds to AS. Thus, the factor analyses of the ACQ may be taken as evidence that AS is unifactorial.

The ACQ asks subjects to indicate the frequency of each cognition when he/she is anxious. The responses are ambiguous; they may reflect thoughts about the consequences of anxiety (i.e. AS cognitions) or cognitions that cause anxiety. The social/behavioral factor may represent cognitions that cause anxiety (i.e. beliefs about the consequences of negative evaluation). Consistent with this interpretation, Arrindell (1993) found the social anxiety scale of the Fear Survey Schedule-III (Wolpe & Lang, 1964) had a medium-to-large correlation with the ACQ social/behavioral factor (r = 0.45), and a small correlation with the ACQ physical concerns factor (r =0.20). [Cohen's (1988) scheme was adopted here to classify the magnitude of correlations.]

Results of factor analyses of the BSQ are further consistent with the argument that AS is unifactorial. The BSQ assesses a range of feared sensations, such as those corresponding to the "domain specific appraisals" proposed by Telch et al. (1989a); i.e. fears of cardiopulmonary sensations, fears of cognitive incapacitation, etc. Yet, the BSQ has a high internal consistency (Chambless et al., 1984) and is unifactorial (Arrindell, 1993).

Other measures o f anxiety sensitivity

Kenardy, Evans and Oei (1992) developed the Anxiety Symptoms and Beliefs Scale, which they administered to 335 anxiety-disordered patients. This scale consists of 16 items assessing the intensity of anxiety-related sensations and 5 items assessing feared consequences of panic or extreme anxiety. The items were factor analyzed and four factors were obtained: (1) vestibular symptoms, (2) respiratory symptoms; (3) fear of losing control or looking foolish; and (4) autonomic arousal. The authors took this result as evidence that AS is multidimensional.

This conclusion is flawed for several reasons. The scale confounds the intensity of anxiety-related sensations with feared consequences of panic/anxiety. Most items (16 out of 21) assessed the intensity of anxiety-related bodily sensations. Four out of 5 items assessing feared consequences of panic/anxiety loaded on factor 3. The remaining factors were primarily or entirely measures of the intensity of bodily sensations, not the f ear of these sensations. Most feared consequences loaded on a single factor, which is consistent with the single factor conceptualization of AS. However, there were too few items assessing feared consequences of anxiety to adequately assess the dimensionality of AS.

A stronger case for the multidimensionality of AS can be made from the findings of Hoffart, Friis and Martinsen (1992). They developed the Agoraphobic Cognitions Scale, which assesses the extent the subject is frightened of 10 aversive consequences of anxiety (e.g. fainting, dying, going crazy, making a scene). The scale was administered to 139 patients with anxiety disorders and/or unipolar mood disorders. Factor analysis yielded three factors: (1) fear of bodily incapacitation; (2) fear of losing control; and (3) fear of acting in an embarrassing manner. It is possible an excessive number of factors were extracted, since the authors used the eigene value >1 rule. However, it is noteworthy that the factors correspond to each of the feared consequences of anxiety postulated by Reiss (1987, 1991); i.e. fears that anxiety has harmful somatic, psychological or social consequences. Even if we adopt a narrow definition of AS (i.e. excluding factor 3), Hoffart et al.'s results still suggest AS is multifactorial. Given the possibility of overfactoring, the study merits replication using a more appropriate rule to select the number of factors, such as the scree test or parallel analysis (Zwick & Velicer, 1986). If replicated, then it would appear that AS is not a "fundamental" fear; it may be composed of still more basic fears. This will be taken up in a later section.

Conclusions

Studies of the ASI and BSQ suggest that AS is unifactorial. Studies of the ACQ have been taken as evidence that AS is composed of two factors. However, an equally plausible possibility is that one of the ACQ factors corresponds to fear of negative evaluation rather than AS. Recent findings by Hoffart et al. (1992), using a newly developed Agoraphobic Cognitions Scale, suggest a 3-factor solution, with separate factors corresponding to fears that anxiety has aversive somatic, psychological and social consequences.

248 Steven Taylor

How are we to reconcile these findings? Regardless of whether we adopt a broad or narrow definition of AS, we are still faced with the fact that some studies indicate that AS is unifactorial, while the others suggest it is composed of two or three factors. Hoffart et al. (1992) found their factors had moderate-to-large correlations with one another (rs 0.36-0.49). This suggests that AS may be multifactorial at the level of first-order factors, and these factors may load on a single second-order factor. This model reconciles the different results; studies of the ASI and BSQ examined AS at the level of the second-order factor, while Hoffart et al. examined AS at the level of first-order factors. The hierarchic model of AS was first proposed by Lilienfeld, Turner and Jacob (1993), although they proposed different first-order factors [based on the solution of Telch et al. (1989a)] and were apparently unaware of the study by Hoffart et al. (1992).

IS ELEVATED ANXIETY SENSITIVITY ASSOCIATED WITH PANIC ATTACKS?

AS is thought to drive the vicious cycle of panic (Clark, 1986; Reiss, 1991). Thus, we expect that people with panic attacks should be characterized by elevated AS. If this was not the case, then the theories of Reiss and Clark would be called into question.

Noncl in ical samples

Several studies have examined the relationship between AS and nonclinical panic. Stewart et al. (1990) has 216 college students complete the ASI and the Panic Attack Questionnaire [PAQ: Norton, Dorward & Cox 0986)]. Eight Ss with high AS (ASI mean score -- 38) were compared with 8 Ss with low AS (mean score = 7). None of the low AS Ss had a history of panic attacks, and only 1 of the high AS Ss had ever panicked. Similar findings were reported by Stewart, Knize and Pihl (1992). Nonclinical panickers (n = 22) and nonpanicking controls (n = 94) did not differ in their scores on the ASI (mean scores = 19 and 18, respectively).

It may have been that these studies did not have a sufficiently large samples to reliably determine the relationship between panic attacks and AS. This interpretation is supported by subsequent studies, which used larger samples. Telch et al. (1989a) administered the ASI and a measure of panic attacks to 842 college students. Ss were classified as panickers (n = 20), infrequent panickers (n = 77) or nonpanickers (n = 745). Panickers and infrequent panickers differed in that the former reported four or more panics in a four-week period or had at least a month of persistent worry about panic). Panickers had higher ASI scores than infrequent panickers and nonpanickers.

Donnell and McNally (1990) administered the AS| and a modified version of the PAQ to a sample college students, whose AS levels were classified as high (n = 68), medium (n = 262) or low (n = 59). In this and later studies (see below), high AS was defined as ASI scores _> 27, medium AS was defined by scores 10-26, and low AS by scores _< 9. Thirty-two percent of high AS Ss reported a history of unexpected panic attacks, compared with 16% and 5% of Ss in the medium and low AS groups, respectively. It is of interest to note that two-thirds of Ss with high AS had never experienced an unexpected panic. This suggests that elevated AS is not simply a consequence of panic.

The relationship between AS and panic may have been underestimated by Donnell and McNally (1990) because they assessed unexpected panics but not cued (expected) panics. The two types of panic are very similar in phenomenology and may have common mechanisms (Norton, Cox & Malan, 1992). Accordingly, Cox, Endler, Norton and Swinson (1991) administered the PAQ (assessing both types of panic) and ASI to a sample of college students. Ss were classified as high (n = 82), medium (n = 165) or low on AS (n = 18). Fifty percent of high AS Ss reported panic attacks in the past year (cued or unexpected panics), compared with 20% and I 1% in the medium and low AS groups, respectively.

Similar findings were reported by Asmundson and Norton (1993), who administered the Anxiety Questionnaire (Telch, Lucas & Nelson, 1989b) and ASI to a sample of college students. As before, Ss were classified as high (n = 87), medium (n = 314) or low on AS (n = 49). Fifty-seven percent of high AS Ss reported a history of panic attacks (cued or unexpected), compared with 30% and 29% in the medium and low AS groups, respectively.

Anxiety sensitivity 249

In a small longitudinal study, Maller and Reiss (1992) administered the ASI to 151 college students. Three years later, a subsample of 23 high-AS Ss and 25 low-AS Ss were reassessed with the ASI and PAQ. High AS was associated with a greater incidence of panic attacks and panic disorder. There were four Ss who experienced panic attacks for the first time during the three-year interval; three had high AS beforehand.

In summary, studies of nonclinical samples generally show that elevated AS is associated with an increased incidence of unexpected and cued panic attacks. These findings are consistent with the theories of Reiss (1991) and Clark (1986).

Clinical samples

Panic attacks occur in all anxiety disorders but, of course, are most frequent in panic disorder (Barlow, Vermilyea, Blanchard, Vermilyea, DiNardo & Cerny, 1985). This suggests that AS should be greatest in panic disorder, and AS in other anxiety disorders should tend to be higher than that of normal controls. Several studies have shown that panic-disordered patients have higher ASI scores than normals (Foa, 1988; Rapee, Ancis & Barlow, 1988; Reiss et al., 1986; Stewart et al.. 1992). Panic patients have been found to have higher ASI scores than obsessive-compulsives (Zeitlin & McNally, 1993) and higher scores than mixed samples of other anxiety disorders (ApfeldorC Shear, Leon & Porter, 1994; Reiss et al., 1986). Studies using the ACQ and BSQ have found that panic patients have higher AS than normal controls (Chambless et al., 1984; Craske, Rachman & Tallman, 1986; Foa, 1988). Craske et al. (1986) found a nonsignificant trend for agoraphobics (defined according to DSM-III criteria) to score higher than social phobics on the ACQ. Foa (1988) reported that panic patients, compared to social phobics and patients with generalized anxiety disorder, had higher scores on the ASI, ACQ and BSQ.

Chambless and Gracely (1989) administered the ACQ and BSQ to patients diagnosed with panic disorder (with or without agoraphobia), generalized anxiety disorder, social phobia, obsessive-com- pulsive disorder or unipolar depression (major depression or dysthymia). Compared to the other groups, panic patients had the highest scores on the BSQ and on the physical concerns subscale of the ACQ Panic patients did not differ from other patients on the social/behavioral concerns subscale. If one adopts a broad definition of AS, these results provide only partial support for Reiss' (1991) theory. The results are entirely consistent with the theory if a narrow definition is adopted (i.e. defining the social/behavioral subscale as being largely a measure of fear of negative evaluation. not AS).

Taylor, Koch and McNally (1992a) assessed 313 anxiety disordered outpatients representing the range of DSM-III-R anxiety disorders. Figure 1 shows the mean ASI scores and standard errors for each diagnostic group. The panic-disordered group had significantly greater AS (P < 0.01 ) than all but the group with posttrauamtic stress disorder, for which there was a trend in the predicted direction (P < 0.06). Compared to ASI scores for normal controls (Peterson & Reiss, 1987). all groups had significantly elevated AS (P < 0.006), except the simple phobics (P > 0.1).

40

~- 30 >

I--

z 20

w

× 10 z

0 PANIC

DISORDER PTSD GAD

iljl OCD SOCIAL SIMPLE

PHOBIA PPIOBIA

Fig. 1. Means and standard errors of ASI scores across the anxiety disorders. (PTSD = Posttraumatic stress disorder, GAD = Generalized anxiety disorder, OCD = Obsessive-compulsive disorder). From Taylor et al. (1992a). Copyright 1992, reproduced with the permission of Elsevier Science Ltd. Oxford,

U.K.

250 Steven Taylor

6O

5 o

D- 30 ~ii

;ANIC PTSD GAD OCD SOCIAL SIMPLE DISORDER PHOBIA PHOBIA

Fig. 2. Mean and standard errors of scores on the Spielberger trait anxiety inventory across the anxiety dis- orders. From Taylor et al. (I 992a). Copyright 1992, reproduced with the permission of Elsevier Science Ltd,

Oxford, U.K.

Patients with panic disorder typically have elevated trait anxiety ( c f Chambless, 1985), and so it is important to determine whether elevated AS was a specific feature of panic disorder, or whether it was merely a concomitant of elevated distress. Taylor et al. (1992a) obtained scores on Spielberger's (1983) Trait Anxiety Inventory from 150 of their 313 patients. Figure 2 shows the means and standard errors of the trait anxiety scores for each diagnostic group. Panic patients had higher trait anxiety than simple phobics (P < 0.01), but did not differ from the other groups (P > 0.1). Thus, elevated AS was not simply a concomitant of nonspecific distress.

Finally, as predicted by the theories of Reiss (1991) and Clark (1986), several studies have found that reductions in panic disorder are accompanied by reductions in scores on the ASI (Foa, 1988; McNally & Lorenz, 1987; Shear, Pilkonis, Cloitre & Leon, 1994) and the ACQ and BSQ (Michelson, Marchione, Greenwald, Glanz, Testa & Marchione, 1990).

Conclusions

Findings from studies of nonclinical Ss generally support the conclusion that elevated AS is associated with an increased incidence of unexpected and cued panic attacks. Studies of clinical samples support the conclusion that AS is greater in panic disordered patients compared to patients with other anxiety disorders, patients with unipolar depression, and normal controls. These results support the theories of Reiss (1991) and Clark (1986), which postulate that AS plays a causal role in panic attacks and panic disorder.

IS ANXIETY SENSITIVITY DISTINCT FROM OTHER FUNDAMENTAL FEARS?

The next question is whether AS is distinct from illness/injury sensitivity and fear of negative evaluation. By postulating three fundamental fears, Reiss's theory assumed these fears are distinct from one another; if they were not then it would be more parsimonious to postulate a smaller set of fundamental fears.

There have been two studies relevant to this question. Reiss, Peterson and Gursky (1988) factor analyzed a pool of items from the ASI and the Fear Survey Schedule-II [FSS-II: Geer (1965)]. The FSS-II is a 51-item self-report inventory assessing a range of fears, such as fears of harmless animals, fears of illness and injury, social fears and agoraphobic fears. Three factors were obtained, corresponding to each fundamental fear. This result offers some support for the distinction among fundamental fears. However, this conclusion is weakened by methodological problems. Thirty-nine percent of FSS-II items and 50% of ASI items failed to load on any factor, which indicates that an insufficient number of factors were extracted (Gorsuch, 1983). The pattern of loadings of the first three factors may change with the extraction and rotation of a greater number of factors (Velicer & Jackson, 1990).

A further problem is that factor analysis of items from the ASI and FSS-II is an inappropriate method for determining the factorial structure of fundamental fears. The ASI is a measure of a fundamental fear, whereas the FSS-II assesses common fears and fundamental fears. Thus, the joint

Anxiety sensitivity 251

factoring of the ASI and FSS-II items may yield factors consisting of a mix of common fears and fundamental fears.

Given these methodological problems, it cannot be concluded that the results of Reiss et al. (1988) unequivocally support the distinction among the fundamental fears. The question of whether fundamental fears are factorially distinct is best addressed by factoring items that only assess the fundamental fears [cf. Comrey (1978)]. One approach is to construct internally consistent scales for each fundamental fear, and then pool and factor the items. It may be that some fundamental fears are not distinct. AS and illness/injury sensitivity both pertain to fears of interoceptive stimuli, and so they may form a single factor.

Taylor (1993) administered the ASI, Fear of Negative Evaluation Scale, and Illness/Injury Sensitivity Index to 100 community volunteers. Ss also completed Spielberger's (1983) Trait Anxiety Inventory and the Fear Survey Schedule-Ill (Wolpe & Lang, 1964), which are discussed later. The measures of fundamental fears were developed with content validity as a key criterion. The measures were not constructed so as to be uncorrelated from one another, and so it was appropriate to pool the items from these scales to determine whether they corresponded the three fundamental fears.

Factor analysis consisted of principal components analyses with oblique rotation. Two factor extraction rules were used; the scree test and parallel analysis. Both indicated a three-factor solution accounting for 54% of total variance. The factors had low correlations among one another, with rs ranging from 0.26 to 0.32. The factors closely corresponded to each fundamental fears, thus supporting Reiss's theory. The magnitude of Ioadings suggested the factor solution was likely to be stable (Guadagnoli & Velicer, 1988), and encourage replication using clinical samples.

HOW IS ANXIETY SENSITIVITY RELATED TO COMMON FEARS?

Reiss (1991) proposed that AS plays an important role in panic attacks and, more generally, is an amplification factor in many types of common fears: "People who are afraid of anxiety should develop a fear of any situation in which there is even a small chance/expectation of becoming anxious; because there are many such situations, people who are extremely sensitive to anxiety should develop fears of many situations" (p. 147). An alternative possibility is that AS plays a role only in panic attacks and agoraphobia.

In a series of factor analytic studies replicated across gender, assessment instruments, and nationalities, Arrindell and colleagues [e.g. Arrindell, Emmelkamp & van der Ende (1984); Arrindell, Pickersgill, Merkelbach, Ardon & Cornet (1991); Arrindell & van der Ende (1986)] found four main dimensions of fear: (1) social fears; (2) fears of injury, illness, blood, and surgical procedures; (3) animal fears; and (4) agoraphobia. The explanatory power of Reiss's theory depends on its ability to account for the variance in these dimensions of fear.

Using a sample of college students, Reiss et al. (1986) found the ASI accounted for 35-50% of variance in FSS-II total scores. Reiss et al. (1988, Study 2) found the ASI and a measure of injury/illness sensitivity accounted for 27% and 34% of the variance, respectively, in responses to a short scale assessing a range of different fears. The sum of the sensitivity measures accounted for 42% of the total variance. McNally and Lorenz (1987) found the ASI accounted for 41% of the variance in the FSS-II total score.

Few studies have examined whether the fundamental fears can account for specific dimensions of common fears. Watson and Friend (1969) found the fear of negative evaluation accounted for 10-26% in variance of social fears, such as fears of writing or eating in public. Leary (1983) reported similar findings. McNally and Lorenz (1987) found the ASI accounted for only 4% of variance in responses to the agoraphobia subscale of the Fear Questionnaire (Marks & Mathews, 1979). Since all their Ss were agoraphobic, the result was probably an underestimation due to severe range restriction.

McNally and Louro (1992) compared simple phobics and agoraphobics, who all had fears of flying. Agoraphobics were more likely to report they were frightened of flying because they feared that enclosure in the aircraft would precipitate a panic attack. In other words, fear of flying, as part of the agoraphobia syndrome, appeared to arise from AS. Simple phobics were more likely to report they feared flying because of fears the plane might crash (i.e. illness/injury

252 Steven Taylor

sensitivity). This suggests that fear of flying may be due to AS only when it is part of an agoraphobia syndrome.

McNally and Steketee (1985) found that many severe animal-phobics were frightened of animals because exposure elicited panic attacks. This suggests that AS may play a role in severe animal phobia. Similarly, Taylor et al. (1991) found that university studients with intense spider fears had elevated AS, when compared to the norms provided by Peterson and Reiss (1987). In contrast, Taylor et al. (1992a) found the ASI scores of simple phobics did not differ from Peterson and Reiss' ASI norms. The patients in the latter study presented with a variety of phobias, although many (35%) presented with fears of blood, injury or choking. Only 13% presented with animal phobia. In all, these results suggest that elevated AS may play an important role in agoraphobia and severe animal-phobias, and may be less likely to play a role in other types of phobia.

Taylor (1993) examined the relationship between fundamental fears and the four dimensions of common fears assessed by the FSS-III (i.e. social fears, agoraphobia, animal fears and blood-injury fears). The FSS-III scales were modified so the items of the social fear scale were distinct from items assessing fear of negative evaluation, and items of the blood-injury fear scale were distinct from items assessing illness/injury sensitivity. That is, the social fear scale did not assess fear of negative evaluation, but assessed fears of inherently non-aversive social stimuli such as eating, writing, or speaking in public. The blood-injury scale did not measure fears of personal injury or illness. Rather, it assessed fears of external stimuli, such as hospitals, doctors, witnessing other people receive injections and so forth [see Taylor (1993) and Watson & Friend (1969) for further information on these distinctions].

The sample consisted of the 100 community volunteers described earlier. Fundamental fears were represented by the three factors derived from the factor analysis of the ASI, Fear of Negative Evaluation Scale and Illness/Injury Sensitivity Index (described in the previous section). The AS factor was correlated with the FSS-III agoraphobia scale (r = 0.33, P < 0.01), but not with the other FSS-III scales (rs < 0.19, P > 0.05). The correlation between AS and the FSS-III animal fears scale was only 0.06 (P > 0.1). Canonical correlation analysis revealed that all fundamental fears except AS were associated with general fearfulness, and AS was associated only with agoraphobia.

These studies show that AS is correlated with agoraphobia. Since agoraphobia typically arises from fear of panic attacks or fear of limited-symptom attacks (American Psychiatric Association, 1994), these results are consistent with the conclusion that AS plays an important role in panic attacks and panic disorder. The results offer mixed support for the relationship between AS and other fears. Elevated AS is associated with intense animal-phobia (McNally & Steketee, 1985; Taylor et al., 1991). Taylor (1993) found that AS was unrelated to social fears, blood-injury fears and animal fears, The sample in the latter study consisted of community volunteers, not anxiety-disordered patients, and so it is possible the correlations were attenuated to some degree by range restriction. Overall, the results of these studies suggest that AS is more strongly related to agoraphobia than to other types of common fears.

Structural relationships among anxiety sensitivity and agoraphobic fear and avoidance

Taylor and Rachman (1992) used structural equation modeling to further evaluate the relationships among AS, agoraphobic fear and agoraphobic avoidance. We tested a model proposing that AS amplifies agoraphobic fear and promotes agoraphobic avoidance, and that agoraphobic fear promotes agoraphobic avoidance. The model was tested using the responses of 330 university students who completed measures of AS and agoraphobic fear and avoidance.

Figure 3 shows the path diagram of the obtained model, with path coefficients and their standard errors. For clarity, the figure shows only the path coefficients of the structural model, omitting those of the measurement model. The model had a good overall fit to the data, and all path coefficients were significant. Path coefficients are weights that indicate the strength of the hypothesized causal relationship. According to the model, a 1.00 SD increment of AS produces a 0.36 SD increase in agoraphobic fear and a 0.25 SD increase in agoraphobic avoidance.

In future studies it would be of interest to take this work further to examine the relationships among AS, agoraphobia and panic. Reiss's theory states that AS directly amplifies agoraphobia, and also contributes to panic. Panic, in turn, is thought to exacerbate AS and also promote

Anxiety sensitivity

FEAR Of THE SUBJECTIVE EXPERIENCE OF ANXIETY

FEAR OF ANX.- RELATED BODILY SENSATIONS

I ALONE I IACCO"PAN'EDI

Fig. 3. Path diagram of structural equation model, which represents the hypothesized causal pathways between anxiety sensitivity and agoraphobic fear and avoidance. All path coett~cients are significant (P < 0.0001). From Taylor & Rachman (1992). Copyright 1992, reproduced with permission of Elsevier

Science Ltd, Oxford, U.K.

253

agoraphobic fear and avoidance. This model, depicted in Fig. 4, proposes reciprocal causation between AS and panic. A longitudinal multiple-wave study could be used to test this model.

W H A T IS T H E R E L A T I O N S H I P B E T W E E N A N X I E T Y S E N S I T I V I T Y A N D T R A I T A N X I E T Y ?

Lilienfeld et al. argued that the ASI is simply a measure of trait anxiety:

"We argue that the results of these studies can be equally accounted for by positing that the ASI measures trait anxiety" (Lilienfeld, Jacob & Turner, 1989, p. 101).

"Results of most of the studies on the ASI... appear to be equally consistent with the more parsimonious hypothesis that the ASI simply measures trait anxiety" (Jacob & Lilienfeld, 1991, p. 75).

This argument, and the implication that AS is nothing more than trait anxiety, was refuted in several articles (McNally, 1989; Taylor, 1993; in press; Taylor et al., 1991). McNally (1989) pointed out that trait anxiety is a general tendency to respond fearfully to stressors, whereas AS is a specific tendency to respond fearfully to anxiety sensations. Taylor et al. (1991) reviewed the studies correlating the ASI and measures of trait anxiety, and found a median correlation of 0.46 between the two. Thus, the median overlap in variance was only 21%. Taylor et al. also found the ASI and Spielberger's Trait Anxiety Inventory were factorially distinct from one another. This conclusion held for psychiatric and college student samples. In both samples the ASI and trait anxiety factors were correlated 0.39 (15% overlapping variance).

Fig. 4. Hypothesized relationship between anxiety sensitivity, panic attacks and agoraphobia.

254 Steven Taylor

Lilienfeld et al. (1993) subsequently retracted their claim that the ASI is simply a measure of trait anxiety. Instead they proposed that the fundamental fears (including AS) and trait anxiety were hierarchically related:

"'AS is a lower-order trait that is nested hierarchically within a higher-order dimension of trait anxiety • . . According to the hierarchical model proposed here, trait anxiety can be conceptualized as a general tendency to react anxiously to potentially anxiety-provoking stimuli, whereas AS is a more specific tendency to react anxiously to one's own anxiety and anxiety-related sensations" (Lilienfeld et al., 1993, p. 171).

Illness/injury sensitivity and fear of negative evaluation also were said to nest hierarchically within trait anxiety. In other words, according to this model, there is a general trait of anxiety proneness, and lower-order factors representing proneness to specific sorts of fears. The lower- order factors share some variance with the higher-order factor, but also have their own unique variance. The model is shown in Fig. 5, and was tested with confirmatory factor analysis, using responses from the 100 community volunteers (Taylor, in press). Recall that these Ss completed the ASI, Fear of Negative Evaluation Scale, Illness/Injury Sensitivity Index, and Trait Anxiety Inventory. Due to limitations of software and hardware, six items from each of these scales were used to define each latent variable [i.e. the ellipses in Fig. 5; see Taylor (in press) for details].

In the figure, the terms U1, U2 etc. corresponded to uniqueness terms, and D1, D2, D3 correspond to disturbance items (Bollen, 1989). Thus, Fig. 5 shows that each item (i.e. TI, T2, FI, F2, etc.) was hypothesized to be composed of unique variance (U1, U2, etc.) and variance due to the fundamental fears. In turn, the fundamental fears contain unique variance (D1, D2, etc.) and variance due to the higher-order factor (trait anxiety).

The model had an acceptable goodness-of-fit and all loadings were significant. Figure 5 shows the loadings of the fundamental fears on the higher-order trait anxiety factor. For clarity, loadings for the measurement model are omitted. These results support Lilienfeld et al.'s (1993) hypothesis that fundamental fears and trait anxiety are hierarchically structured.

Despite these encouraging findings, the model remains descriptive rather than explanatory. If the model is to serve as a useful explanatory framework for understanding fear, then it is important to further specify the nature of the relationships among trait anxiety and fundamental fears. For example, what are the causal relationships (if any) between trait anxiety and fundamental fears? Lilienfeld et al.'s model implies that trait anxiety exerts some form of causal influence over

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Fig. 5. Path diagram and loadings for a confirmatory factor model, which hypothesizes that fundamental fears are nested within trait anxiety. All loadings are significant (P < 0.002). From Taylor (in press).

Copyright 1994, reproduced with the permission of Elsevier Science Ltd, Oxford, U.K.

Anxiety sensitivity 255

fundamental fears (i.e. fundamental fears contain variance due to trait anxiety). However, it is not clear how this would occur.

An alternative account, which is equally consistent with the results of the confirmatory factor analysis (Fig. 5), is that AS and other fundamental fears are causes of trait anxiety. In other words, the general disposition to become anxious (trait anxiety) may be determined by tendencies to become anxious about specific types of stressors. Fundamental fears are instances of the latter. People with intense fundamental fears are made anxious by a variety of stimuli, and so tend to display high levels of anxiety proneness. Regression analysis indicated that the measures of fundamental fears accounted for 41% of variance in the Trait Anxiety Inventory (Taylor, 1993).

G E N E R A L C O N C L U S I O N S

From the studies reviewed in this article, we can draw five conclusions, which address each of the questions raised at the outset:

I. AS is a unitary construct at a higher-order level, and may be multidimensional at a lower-order level. If one adopts a broad definition of AS, the lower-order dimensions correspond to each of three feared consequences of anxiety: (1) somatic harm (e.g. death); (2) psychological harm (e.g., insanity); and (3) social harm (e.g., ostracism). If we adopt a narrow definition of AS, then the lower-order factors correspond to factor l and 2, but not 3. These conclusions are tentative, pending further work on the factorial structure of AS.

2. Elevated AS is associated with panic attacks. Indeed, people with panic disorder tend to have higher AS than people with other anxiety disorders and normal controls.

3. AS is distinct from other "fundamental" fears. 4. AS is more strongly related to agoraphobia than to other "common" fears. 5. AS is distinct from trait anxiety, but the two appear to be hierarchically organized, as

postulated by Lilienfeld et aL (1993). The causal nature of this organization remains to be determined; may be that AS (and other fundamental fears) are causes of trait anxiety.

F U T U R E D I R E C T I O N S

The findings covered in this review support and extend Reiss's theory, and also raise some important issues for further investigation.

1. How does AS develop, and does a developmental analysis shed light on the dimension(s) of AS? AS, like other fears, may be acquired by observational learning, verbal information, or traumatic experiences (Rachman, 1990). People may tend to learn to fear some anxiety-related sensations but not others (e.g. palpitations but not dizziness or derealization). This would support a multidimensional model of AS consisting of orthogonal (uncorrelated) dimensions. Alternatively, people who learn to fear one set of anxiety-related sensations also may tend to learn to fear others. This would support a unidimensional model of AS, or a hierarchical model consisting of multiple correlated factors.

2. Alternative measures of AS may further our understanding of the fear of anxiety. It may prove fruitful to develop structured interviews of AS, since interview methods are a rich source of data. Vasey and Borkovec (1992) developed a "catastrophizing assessment," which is an interview-based method for assessing feared consequences associated with worry. This method could be readily applied to the assessment of AS.

Beliefs about the dangerousness of anxiety symptoms could be assessed with methods used in the assessment of delusions [e.g. Chadwick & Lowe (1994)]. The development and modifications of AS could be investigated by assessing the strength of beliefs that anxiety-related sensations are dangerous, and by assessing how these beliefs are changed or maintained in the face of corrective information. For example, do the beliefs get stronger when subject to weak therapeutic challenges (i.e. an inoculation effect): This type of assessment may provide important clues as to the best way to reduce excessive AS.

256 Steven Taylor

3. Finally, the concept of "fundamental" fears requires further work at a conceptual and empirical level. Is AS really a fundamental fear or is it often secondary to other fears? Recall that Reiss proposed that AS is the fear of anxiety symptoms arising from beliefs that anxiety has harmful somatic, social and psychological consequences. This suggests that AS can be logically reduced to still more basic fears, such as fear of negative evaluation, fear of pain/death and fear of insanity.

Further research on these issue may advance our understanding of panic, phobia and other anxiety reactions.

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