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Page 1: Is the state-trait anxiety inventory multidimensional?

,%.ron & fnd Lhfl Vol I. pp. 101 10 214 c) Pcrgamon Prcrr ~_td. 1980 Printed in Great Britain

0191.XXh9/80/0701-0207102 W 0

IS THE STATE-TRAIT ANXIETY INVENTORY MULTIDIMENSIONAL?

PETER R. VAGG and CHARLES D. SPIELBERGER

University of South Florida, Tampa

and

THOMAS P. O’HEARN, JR

Lackland Air Force Base, San Antonio, Texas

(Received 5 November 1979)

Summary-The factor structure of the State-Trait Anxiety Inventory (STAI) was investigated to determine whether the STAI State and Trait Anxiety scales were multidimensional. The STAI (Form Y) was administered to a heterogeneous sample of Air Force recruits (N = 1728); the scores for all 40 STAI items were factor-analyzed together, using the principal axis method and varimax rotation. Two- and four-factor solutions were found to be equally good in simple structure and psychological meaningfulness. Clearly defined state and trait anxiety factors were found in the more parsimonious two-factor solution. In the four-factor solution, the factors were: State Anxiety-Present, State Anxiety-Absent, Trait Anxiety-Present and Trait Anxiety-Absent. Using Cattell’s (1966) confactor method, these factors were found to be congruent with similar factors previously identified for high school students by Spielberger et al. (1980). The anxiety- present and anxiety-absent factors were interpreted as reflecting either ‘item method’ variance or ‘item-intensity specificity’. There was no evidence in the present study that the STAI scales were multidimensional in terms of item content.

Almost 20 years ago, Cattell and Scheier (1961) distinguished between anxiety as a transitory emotional state (S-Anxiety) and as a relatively stable personality disposition or trait (T-Anxiety). The State-Trait Anxiety Znoentory (STAB was subsequently developed by Spielberger, Gorsuch and Lushene (1970) to provide operational measures of state and trait anxiety. In responding to the STAI S-Anxiety scale, subjects are instructed to indicate the intensity of their feelings of anxiety at a particular moment; the T-Anxiety scale requires respondents to describe how they generally feel by reporting the frequency of specified symptoms of anxiety. Both scales contain items that describe symptoms of anxiety (e.g. “I feel nervous”), as well as items that indicate the absence of anxiety (e.g. “I feel calm”).

During the past six years, the STAI has been employed more frequently in psychologi- cal investigations than any other anxiety inventory (Buros, 1978). Although the STAI

S-Anxiety and T-Anxiety scales were interpreted as unidimensional measures in most of these studies, several investigators have used the technique of factor analysis to examine the possibility that these scales might be multidimensional. The findings in the eight published factor studies of the STAI have been characterized by great diversity: as few as ttio and as many as eleven different factors have been reported. In keeping with these results, Endler, Magnusson and their colleagues (Endler and Magnusson, 1976; Endler et al., 1976) have argued on the basis of their findings in two recent factor analytic studies that the STAI S-Anxiety and T-Anxiety scales are multidimensional. The present study attempts to clarify the factor structure of the STAI by evaluating the existing literature and presenting some new empirical findings.

ANALYSIS OF RESEARCH ON THE FACTOR

STRUCTURE OF THE STAI

In four studies in which all 40 original STAI items were factored together (Barker et

al., 1977; Gaudry and Poole, 1975; Gaudry et al., 1975; Kendall et al., 1976). the items

207

Page 2: Is the state-trait anxiety inventory multidimensional?

208 PETER R. VAGG. CHARLES D. SPIELBERGER and THOMAS P. O’HEARN. JR

from the STAI S-Anxiety and T-Anxiety scales consistently loaded on different factors. Gaudry et al. and Kendall et al. found a single trait anxiety factor that was loaded exclusively by T-Anxiety items. The single second-order trait anxiety factor reported by Gaudry and Poole was defined by six first-order factors, which were each comprised almost entirely of T-Anxiety items. In the Barker et al. study, two trait anxiety factors were identified: one consisted primarily of trait anxiety-absent items (e.g. “I am content”, “I feel secure”), while the other was loaded primarily by trait anxiety-present items (e.g. “I worry too much over something that really doesn’t matter”).

Distinctive state anxiety factors were also found in all four studies that factored the 40 original STAI items. Barker et al. identified a single state anxiety factor. Gaudry and Poole found a single second-order state anxiety factor defined by four first-order factors which were comprised almost entirely of S-Anxiety items. Gaudry et al. identified four state anxiety factors; three of these factors consisted entirely of S-Anxiety items associ- ated with one of three different administrations of the scale, while the fourth consisted of state anxiety-absent items representing all three occasions of measurement. Kendall et al.

found two state anxiety factors: a state anxiety-absent factor similar to the one reported by Gaudry et al. and, in addition, a state anxiety-present factor.

In separate factor analyses of the STAI T-Anxiety and S-Anxiety items, Endler and Magnusson, and Endler et al., identified three trait and three state anxiety factors. Loo (1979) factored only the 20 T-Anxiety items and identified four factors, According to Endler and Magnusson, two of their trait factors were invariant across sex and cultural groups; but a careful inspection of the results of this study revealed substantial differ- ences in the pattern of loadings of items defining factors that were given the same names in different samples (e.g. see Endler et al., Table 3, pp. 84-85). This same criticism also seems to apply to the three state anxiety factors identified by Endler and Magnusson (e.g. see Endler et al., Table 5, p. 88). Two of the trait factors reported by Loo that were given identical labels for males and females also appeared to be unstable across sex.

It was also evident in the Endler and Magnusson studies that several items had salient loadings on two or more factors. Since the assignment of items to factors by Endler and Magnusson was ambiguous, the soluttons they reported had poorly defined simple struc- ture. If fewer factors had been extracted, it is possible that the simple structure of Endler and Magnusson’s solutions would have improved, which might also have resulted in more parsimonious and psychologically-meaningful solutions. Moreover, in both of their studies the eigenvalues of the first unrotated factor were nearly four times as large as the eigenvalues of the second unrotated factor, thus providing some support for the undi- mensionality of the STAI S-Anxiety and T-Anxiety scales. Unfortunately, Endler and Magnusson did not report item loadings for the two-factor solutions, so it is not possible to compare their findings with the state and trait anxiety-present and anxiety-absent factors that were identified in those studies in which all 40 STAI items Were factored together.

In a recent study of the factor structure of the STAI, Spielberger et al. (1980) adminis- tered Form X of the STAI to more than 400 high school students and conducted separate factor analyses of the responses of male and female subjects. Three factors were identified for each sample. For the males, these were State Anxiety, Trait Anxiety-Present and Trait Anxiety-Absent. State Anxiety-Present and Trait Anxiety-Present factors were obtained for the females, along with a single Anxiety-Absent factor that included both state and trait items.

Spielberger et al. (1980) also observed that several of the original STAI (Form X) items had poor psychometric properties and/or confounded the concepts of depression and anxiety. These items were replaced, and the revised 40-item STAI (Form Y) was adminis- tered to a large sample of high school students. In separate factor analyses of all 40 STAI-Y items for males and females, four factors were identified for both sexes: State Anxiety-Present, State Anxiety-Absent, Trait Anxiety-Present and Trait Anxiety-Absent.

The present investigation reports the results of two studies undertaken to further clarify the factor structure of the revised STAI (Form Y). In the first study, the STAI-Y

Page 3: Is the state-trait anxiety inventory multidimensional?

Is the State-Trait Anxiety Inventory multidimensional? 209

was administered to a large sample of male Air Force recruits in an attempt to replicate the findings of Spielberger et al. (1980). The second study used Cattell’s (1966) confactor method to compare the results of the factor analysis of the STAI-Y for Air Force recruits with the factors reported by Spielberger et al. (1980) for high school males.

STUDY I

Subjects and procedures

The subjects were 1728 male U.S. Air Force recruits assigned for basic training to the Lackland Military Training Center in San Antonio, Texas. The revised STAI (Form Y) was administered with standard instructions (Spielberger et al., 1970) to groups of 90 to 300 recruits by Air Force personnel. Since the recruits were tested within one or two days of first reporting for duty, the inventory was administered under conditions that were considered stressful.

Responses were recorded on IBM machine-scored answer sheets. The data for 27 subjects who failed to respond to three or more S-Anxiety or three or more T-Anxiety items were eliminated from the study. For subjects who failed to respond to one or two items on either scale, a value of ‘2’ was assigned as the score for each omitted item. The scores for the 40 STAI-Y items were intercorrelated and factor-analyzed using the princi- pal axis method of factor extraction, with squared multiple correlations as estimates of the communality.

Cattell’s (1966) ‘scree test’ and the ‘breaks’ criterion, suggested by Cliff and Hamburger (1967) and Pennell (1968) were used in determining the number of factors to be extracted. An optimal factorial solution was defined as satisfying both Thurstone’s (1947) and Kaiser’s (1958) notions of simple structure, according to which each variable (item) should load unambiguously on one, and only one, factor. In an optimal solution, the factors should also reflect meaningful psychological concepts and be interpretable within the context of some theoretical network.

Results

The means, standard deviations, and alpha coefficients for the STAI-Y S-Anxiety and T-Anxiety scales are reported in Table 1, where they are compared with similar data reported by Spielberger et al. (1980) for high school males. The S-Anxiety scores for the Air Force recruits were significantly higher than those of the high school students, while the high school students scored significantly higher in T-Anxiety than the Air Force recruits. The alpha coefficient for S-Anxiety was higher for the Air Force recruits (0.93) than for the high school students (0.86): the alphas for the T-Anxiety scale were 0.90 for both samples.

The responses of the Air Force recruits to the 40 STAI-Y items were factor analyzed using the Statistical package for the social sciences (SPSS: Nie et al., 1975). The

Table 1. Means, standard deviations and alphas for the STAI-Y State Anxiety and Trait Anxiety Scales for the Air

Force recruits and high school students

Air Force High school (N = 1701) (N = 202) t-Test

State Anxiety Mean SD Alpha

Trait Anxiety Mean SD Alpha

43.50 40.17 3.t33t 11.95 10.53 0.93 0.86

37.83 39.45 2.93* 9.45 9.74 0.90 0.90

l p < 0.01. t p < 0.001.

Page 4: Is the state-trait anxiety inventory multidimensional?

210 PETER R. VAGG, CHARLES D. SPIELBERCER and THOMAS P. O’HEARN, JR

Table 2. Salient loadings for the two and four factor solutions based on factor analyses of the STAI-Y for Air Force recruits*

STAI-Y item

Two-factor solution Four-factor solution

I II I II III IV

01 02 03 04 05 06 07 08 09 10 11 I2 13 I4 I5 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

Factor

Unrotated eigenvalue

0.64 0.59 0.68 0.54 0.66 0.59 0.49 0.54 0.58 0.67 0.42 0.66 0.59 0.46 0.68 0.48 0.61 0.57 0.58 0.60

0.36 State

Anxiety

12.25

0.60 0.51 0.62 0.36 0.50 0.56 0.63 0.48 0.43 0.72 0.46 0.46 0.70 0.47 0.46 0.60 0.37

(0.32) 0.54 0.38

Trait Anxiety

3.19

0.54 0.60 0.39

0.64

0.59

0.71 0.39

0.38

0.57 0.44

0.52 0.39

0.56

0.70 0.64 0.40

0.69 0.64

0.49 0.37 0.47

0.60 0.65

0.63 0.45 0.59

(0.28) 0.36 0.56 0.66

0.73

0.67 0.45

0.60

0.49

State Trait Anxiety Anxiety absent absent 12.25 3.19

0.41

0.49 0.51

0.62 0.38

0.43

0.59 0.43

0.47 State Trait

Anxiety Anxiety present present

2.39 1.19

* Only salient loadings above 0.35 are reported, except that when an item had no salient loadings, its highest loading is indicated in parentheses.

scree/breaks criteria suggested that two to four factors should be rotated: however, to ensure that no meaningful solution was overlooked, two to five factors were rotated by varimax. Each of the resulting solutions was examined for simple structure, parsimony and psychological meaningfulness. The two- and four-factor solutions had good simple structure and could be meaningfully interpreted. These solutions are presented in Table 2, in which the loadings for salient items are reported. (An item was considered salient if it had a loading of 0.35 or greater.) The name given to each factor is indicated at the bottom of the table. In the two-factor solution, all 20 S-Anxiety items had salient load- ings on Factor I, and 19 of the 20 T-Anxiety items had salient loadings on Factor II. (The highest loading for the single nonsalient T-Anxiety item was also on this factor.) Further- more, as can be seen in Table 2, only one item (No. 40) had salient loadings on both factors. Thus, the two-factor solution provided strong support for the conceptual distinc- tion between state and trait anxiety.

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Is the State-Trait Anxiety Inventory multidimensional? 211

In the four-factor solution, Factor I was comprised entirely of state anxiety-absent

items; the highest loadings were for item 10 (“I feel comfortable”) and item 15 (,,I am

relaxed”). Factor II consisted almost entirely of trait anxiety-absent items; the items with the highest loadings were 30 (“I am happy”) and 33 (“I feel secure”). Factor III was defined exclusively by state anxiety-present items (12, “I feel nervous; 13, “I am jittery”), and Factor IV was comprised primarily of trait anxiety-present items (31, “I have dis- turbing thoughts*‘; 37, “Some unimportant thought runs through my mind and bothers me”). Thus, in the four-factor solution the state and trait anxiety factors which were identified in the two-factor solution were subdivided into anxiety-present and anxiety- absent factors.

The five-factor solution was examined and considered unsatisfactory. In addition to the four factors described above, this solution included a poorly-defined “self-confidence” factor consisting of only two salient items. The three-factor solution was also judged to be unsatisfactory because it did not have good simple structure, and this solution lacked psychological meaningfulness and parsimony.

STUDY II

Method

The results of the factor analysis of the STAI-Y for the Air Force sample in the present study were compared with the results of the factor analysis of the STAI-Y for 202 male high school students reported by Spielberger et al. (1980). Since a four-factor solution was most satisfactory for the high school students, the degree of similarity between the four factors obtained in the previous study and the four factors identified for the Air Force recruits in the present study was evaluated.

Cattell’s (1966) congruent factors (confactor) approach provides a method for the quan- titative comparison of factors derived from different samples. In essence, the confactor method involves the computation of the correlations between factor scores based on the factors identified in two or more samples. In the present study, factor scores were calcu- lated for each of the four factors identified in the Air Force and high school samples. The items with salient loadings (i.e. 0.35 or larger) on each of the four factors were determined for each sample; item weights of + 1.00 for each salient item and zero for non-salient items were used in calculating the factor scores. The resulting factor scores were then correlated for each sample as well as for the two samples combined (1903 subjects).

Results

The correlations among the factor scores for each sample were quite similar to those found for the combined sample. Therefore, only the correlations for the combined sample are reported in Table 3. The confactor correlations for the combined sample, based on corresponding factors from the Air Force and high school samples, are italicized in the leading diagonal of this table. All of the confactor correlations are greater than 0.90,

Table 3. Correlations for the combined sample (N = 1903) between factor scores derived from separate factor analyses of the STAI-Y for

Air Force recruits and high school males

Air Force males High school males

I II III IV

Factor I State Anxiety absent Factor II Trait Anxiety absent Factor III State Anxiety present Factor IV

0.92 0.50 -0.58 -0.41

0.75 0.92 -0.36 -0.59

-0.54 -0.23 0.94 0.56

Trait Anxiety present -0.53 -0.31 0.70 0.95

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212 PETER R. VAGG. CHARLES D. SPIELBERGER and THOMAS P. O’HEARN, JR

providing striking evidence of the congruence of corresponding factors from the two

samples.* The correlations between non-corresponding factors in the two samples were consider-

ably lower than the confactor correlations, as can be seen in the values of the off- diagonal correlations in Table 3. It is interesting to note, however, that the correlations between factors defined by anxiety-absent items (I and II) and by anxiety-present items (III and IV) were higher than the correlations between factors defined by items with different anxiety-present or anxiety-absent content. For example, the correlation of Factor I (State Anxiety-Absent) for the high school students with Factor II (Trait Anxiety-Absent) for the Air Force recruits was 0.75, while Factor I for the high school males correlated -0.54 and -0.53, respectively, with the anxiety-present factors (III and IV) for the Air Force recruits (see column 1 in Table 3). Similarly, the correlation of Factor III (State Anxiety-Present) for the high school students with Factor IV (Trait Anxiety-Present) for the recruits was 0.70, while this factor correlated only -0.58 and -0.36 with the anxiety-absent factors (I and II) for the recruits.

The eight correlations between the anxiety-absent and anxiety-present factors in Table 3 are all negative, while the eight correlations of anxiety-absent with anxiety- absent factors and of anxiety-present with anxiety-present factors are all positive. These findings provide further support for the conceptual distinction between the anxiety- absent and anxiety-present factors.

DISCUSSION

In the present study, the two-factor and four-factor solutions for the Air Force recruits were found to be equally good in terms of simple structure. The two-factor solution gave clearly defined state and trait anxiety factors, and thus provided strong support for the meaningfulness of the state-trait distinction in the measurement of anxiety. The four- factor solution indicated that the STAI-Y S-Anxiety and T-Anxiety scales were both comprised of two main components which are defined by anxiety-present and anxiety- absent items.

The results of the present study were generally consistent with the findings in five other studies in which all 40 STAI items were factored together and separate state and trait anxiety factors were found (Barker et al., 1977; Gaudry and Poole, 1975; Gaudry et al., 1975; Kendall et al., 1976; Spielberger et al., 1980). Since Endler and Magnusson (1976), Endler et al. (1976), and Loo (1979) factored the S-Anxiety and T-Anxiety items separ- ately, the results of these three studies do not directly contribute to clarifying the findings of distinctive state and trait anxiety factors in the STAI.

Distinctive factors based on the anxiety-absent and anxiety-present content of the STAI items were identified in the four-factor solution in the present investigation. Similar factors have also been found in several previous studies (e.g. Barker er al., 1977; Gaudry an.! Poole, 1975; Gaudry et al., 1975; Kendall et al., 1976; Spielberger et al., 1980), but these factors were confounded with item differences based on the state-trait distinction. Of the eight published studies in which the original form of the STAI (Form X) was factored, none was successful in identifying the state and trait anxiety-present and anxiety-absent factors that were found in the present study.

There appear to be two major reasons why the results of the present study differ from those of previous factor-analytic studies of the STAI. First, all previous studies factored an earlier form of the scale (STAI-X), which included several items with poor psycho- metric properties and others that confounded the concepts of anxiety and depression. Secondly, the STAI-X T-Anxiety scale had 13 anxiety-present items, but only 7 anxiety- absent items; this imbalance has undoubtedly contributed to the inability to identify a stable trait anxiety-absent factor in previous studies.

l The confactor approach was also used to determine the correlations between the four factors identified for the female sample (N = 222) in the Spielberger et al. (1980) study and the corresponding factors identified for the Air Force recruits and the high school males. The set of correlations between the factors identified for the females and the two male samples were similar to those reported in Table 3. All of the confactor correlations were 0.90 or above, demonstrating that the four factors were invariant across sex.

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Is the State-Trait Anxiety Inventory multidimensional? 213

The imbalance in anxiety-present and anxiety-absent items in the children’s form of the STAI (STAIC) may also have contributed to the differences that have been reported in the factor structure of the STAIC. The T-Anxiety scale of the STAIC contains 20 anxiety- present items but no anxiety-absent items, while the STAIC S-Anxiety scale contains 10 items of each type. While this unbalanced ratio of anxiety-present to anxiety-absent items made it impossible for Gaudry and Poole to identify factors in the STAIC similar to those found in the present study, they also appear to have over-factored their data in interpreting 11 first-order factors. In a recent study based on 10 separate samples of children of different ages, Hedl and Papay (1979) factored the STAIC; they identified independent state anxiety-present, state anxiety-absent, and a single trait anxiety factor in all 10 samples.

In the first published factor analysis of the revised STAI (Form Y), Spielberger et al. (1980) found state and trait anxiety-present and anxiety-absent factors for male high school students. The results of the present study showed these four factors to be con- gruent with the factors that were identified for a large sample of Air Force recruits. While the consistent finding of anxiety-present and anxiety-absent factors could be interpreted as evidence of the multidimensionality of the S-Anxiety and T-Anxiety scales, it seems more plausible to interpret these factors as resulting from either ‘item-method variance’ (i.e. the STAI consists of two distinctive types of items, anxiety-present and anxiety- absent), or to ‘item-intensity specificity’ (i.e. the anxiety-present items appear to be more effective in measuring higher levels of state and trait anxiety, whereas the anxiety-absent items are more sensitive at lower levels (Spielberger et al., 1970)). Whatever the case may be, the mechanics of factor analysis identifies differences in the properties of anxiety- present and anxiety-absent items, and produces factors that reflect these differences.

As previously noted, Endler and Magnusson and Endler et al. found three factors for both the STAI S-Anxiety and T-Anxiety scales, and interpreted their results as evidence that the STAI was multidimensional. On the basis of the findings of the present study and similar results reported by other investigators, it seems more likely that Endler, Magnusson and their colleagues have consistently over-factored the STAI, thereby pro- ducing more factors than could be meaningfully or parsimoniously interpreted. More- over, Endler and Magnusson studied relatively small homogeneous samples of college students; for example, they tested only 48 Canadian and 54 Swedish males, compared to 1700 Air Force recruits in the present study. Consequently, the factors they identified were relatively unstable, especially for their male samples, and they neither reported nor discussed any alternatives to the three-factor solutions on which they based their conclu- sion that the STAI was multidimensional.

It should also be noted that Endler and Magnusson (1976) factored the original ver- sion of the STAI (Form X). A careful examination of their results reveals that the factors that they identified (see Tables 7 and 8, pp. 156-157) were strongly influenced by items with depressive content (e.g. 23, “I feel like crying”; 35, “I feel blue’*). These items were replaced in the revised STAI (Form Y) by items with content that was more consistent with Spielberger’s (1966, 1976) theoretical conception of anxiety (e.g. 25, “I feel like a failure”; 35, “I feel inadequate”).

The findings of the present study indicate that the STAI-Y scales are multidimensional only in the sense that anxiety-present and anxiety-absent items defined different factors; there was no evidence of multidimensionality in terms of qualitative semantic differences in item content. While it is clear that the anxiety-present and the anxiety-absent wording of individual STAI-Y items is important in determining the factor structure of the scale, we do not know if it is ‘item-method’ variance or ‘item-intensity specificity’ that produces the anxiety-present and anxiety-absent factors.

The results of the present investigation permit us to provide a tentative but qualified answer to the question posed as the title of this paper: The factor structure of the STAI is defined by strong state and trait anxiety components, and by factors that indicate the presence or the absence of state and trait anxiety. While the results of the factor analysis in the present study, and the demonstration that the factors that were identified were

Page 8: Is the state-trait anxiety inventory multidimensional?

214 PETER R. VAGG, CHARLES D. SPIELBERGER and THOMAS P. O’HEARN, JR

congruent with those obtained for high school students in a previous study, provide strong evidence that the STAI-Y measures distinctive, factorially independent state and trait anxiety concepts, further research will be required to clarify whether the anxiety- present and anxiety-absent factors reflect item-method variance or item-intensity speci- ficity.

Acknowledgements-Work on this paper was supported in part by a contract awarded to C. D. Spielberger by the Advanced Research Projects Agencv. United States Department of Defense (MDA 903-77-C-0190). The authors wish to thank Capi. E. Ry Wiiiiams, Dr. WaIlace‘Bloom, S./Sgt. Charles Adkins, S.&t. William Walker, and the officers and enlisted personnel associated with the Air Force Basic Military Training School, for their assistance in conducting the study, and Greg W. Donham for his help in the analysis of the data.

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