The current study evaluated the psychometric properties of the OASIS, a self-report measure of anxiety severity and impairment. A previous investigation provided evidence for the reliability and validity of the OASIS in a college student sample (Norman et al. 2006
); however, conclusions could not be drawn regarding the utility of the OASIS for assessing anxiety in clinical samples or samples more diverse in age and education level. Our study addressed this limitation by evaluating the OASIS in a diverse sample of primary care patients who were referred to an anxiety treatment study. We conclude that the OASIS has good reliability and validity for clinical samples, as well as applicability to a diverse range of anxiety disorders.
The convergent validity of the OASIS was supported by robust correlations with a well-validated global measure of anxiety (BSI-A) as well as with each of the four disorder-specific measures. The OASIS also showed expected correlations with other constructs that overlap significantly with anxiety. Patients with higher OASIS scores scored lower on mental health and higher on disability. Finally, discriminant validity analyses demonstrated that OASIS scores are not substantially related to scores on measures of other constructs that have minimal overlap with anxiety (e.g., alcohol use).
Overall, our results suggest that the OASIS effectively captures severity and impairment regardless of the specific focus of the anxiety disorder. As noted above, the OASIS displayed salient correlations with measures of generalized anxiety, social anxiety, posttraumatic stress, and panic. In addition, the anxiety disorder identified by the patient as most distressing was not a significant predictor of OASIS scores. In contrast, number of anxiety diagnoses was positively correlated with OASIS score. We view this as supporting the validity of the OASIS, given that prior research has shown that presence of multiple anxiety disorders is associated with greater impairment than presence of a single disorder (Mennin, et al., 2000; Kroenke et al., 2007
The results regarding the internal consistency and dimensionality of the OASIS were similar to those reported for an undergraduate sample (Norman et al. 2006
). We concluded that a single-factor model that accounted for correlated error variance between two items provided the best fit for the data. Therefore, use of a total score (computed by summing the five items) is recommended when the OASIS is used in clinical samples. Statistical analyses to determine an appropriate cut-score for identification of clinically anxious individuals suggested that an OASIS score of 8 or above (which correctly classified 87% of the patients in this sample) would be indicative of a probable anxiety disorder. We did not attempt to statistically determine a cut-score for classifying patients as remitted in the present study, but future investigations that include the OASIS as a treatment outcome measure should address this question.
A common question posed for anxiety scales is how well they can be differentiated from measures of depression. Many well-established anxiety measures correlate significantly with depression scales, and in some cases appear equally sensitive to depression as to anxiety (Moras et al. 1992
; Bieling et al. 1998
). In this sample (largely comprised of clinically anxious individuals), the OASIS correlated with a measure of depressive symptoms (PHQ-9). The magnitude of this correlation (r
= .50) was identical to the correlation between the OASIS and the convergent validity measure of global anxiety symptoms. Hierarchical regression further showed that presence of unipolar mood disorders predicted variance in OASIS scores beyond the variance accounted for by anxiety disorders. In fact, MDD predicted a greater increase in OASIS score than any of the anxiety disorders.
There are several possible explanations for the association between depressive symptoms and more severe profiles on the OASIS. First, having both anxiety and depression may reflect the presence of a more severe diathesis that makes individuals prone to anxiety syndromes of greater severity. Second, presence of more severe anxiety may lead to depression, or conversely presence of depressive symptoms may exacerbate anxiety in some patients. Finally, it is possible that patients do not discriminate well between anxious and depressive symptoms and are considering both when they fill out a questionnaire like the OASIS (i.e., scores are artificially inflated in patients with co-occurring depression).
In practice, the potential influence of depressive symptoms on OASIS scores may cause some patients with mood disorders to score at or above the recommended cut-score of 8, even if they do not meet full criteria for a co-occurring anxiety disorder. As with any self-report scale, the OASIS should not be used in isolation for diagnostic purposes. A “positive” screen on the OASIS should prompt the clinician to inquire about anxiety disorders as well as symptoms of conditions that commonly co-occur with anxiety disorders such as mood disorders. In some cases a mood disorder may be the most appropriate diagnosis for a patient with an elevated OASIS score. This type of clinician-based differential diagnosis, while at times logistically challenging in settings such as primary care, is essential for adequate assessment and treatment planning for patients with anxiety and other psychiatric disorders.
The possible influence of depressive symptoms on OASIS scores may be considered a limitation of the measure, albeit one that applies to many other anxiety assessment tools (see for examples). In the current study we were not able to investigate the most appropriate manner to differentiate presence of anxiety disorders from presence of mood disorders on the OASIS for two reasons. First, the number of patients with mood disorders in the absence of anxiety disorders was low (n = 43). Second, this small sample was likely heavily biased toward cases of “anxious depression” given that the patient’s physician perceived enough anxiety symptoms to refer the patient to an anxiety treatment study. Therefore, it would be invalid to estimate OASIS norms for patients with mood disorders using this sample. Future studies using samples that are not predetermined to have an increased risk of anxiety disorders should evaluate the ability of the OASIS to differentiate anxiety disorders from mood disorders and other conditions.
Several limitations of this study must be noted. First, convergent validity measures consisted solely of other self-report inventories. Therefore, some of the relationships observed between the OASIS and other measures of anxiety may have been attributable to method effects. Future studies should attempt to demonstrate meaningful relationships between the OASIS and measures of anxiety severity that do not rely on self-report. Second, demographic information was only available for participants who were enrolled in the larger CALM study. Because this information is unknown for participants who were ineligible or refused, we cannot assume that the subsamples used for the convergent and discriminant validity analyses were representative of the total sample. Third, the format of the OASIS is such that each response option is linked to 1–3 short sentences describing a certain level of symptoms or impairment. The need to read through these response options may sometimes be burdensome to patients or clinicians interpreting the measure. However, an alternative view is that this format promotes more thoughtful responses on the part of the patient and provides more informative details to the clinician.
In summary, the present investigation suggests that the OASIS is a reliable and valid instrument for measurement of anxiety severity and impairment in clinical samples. These results build upon those of a prior study supporting use of the OASIS for assessment of anxiety in non-clinical samples (Norman et al. 2006
). To the best of our knowledge, this is the only available measure that captures severity and impairment across anxiety disorders
. The combination of its broad applicability and brevity enhance the utility of the OASIS as an assessment tool for primary care, outpatient psychiatric, and other settings that require broad and efficient assessment (e.g., community-based research). In particular, the fact that the OASIS demonstrated a favorable balance of sensitivity and specificity with just five items suggests that the OASIS could be a highly efficient and effective screening tool. In addition to identifying patients with probable anxiety disorders, the OASIS provides valuable information to the clinician regarding severity of symptoms and impairment related to the patient’s anxiety.
Finally, the OASIS also may prove a useful tool for clinical assessment of treatment outcome, especially for patients with multiple anxiety disorders who would otherwise need to complete multiple self-report inventories that might be difficult to integrate and/or prioritize. The recent emergence of behavioral treatments that can be applied to multiple anxiety disorders (Barlow et al. 2004
; Sullivan et al. 2007
) also suggests a need for assessment tools that capture severity and impairment across a variety of anxiety-related problems. Given its applicability to a wide range of anxiety disorders, the OASIS appears to be a promising measure for evaluating the effects of interventions aimed broadly at anxiety rather than one specific anxiety diagnosis.