The Four-Dimensional Symptom Questionnaire (4DSQ): a validation study of a multidimensional self-report questionnaire to assess distress, depression, anxiety and somatization

Characteristic distress symptoms are worry, irritability, tension, listlessness, poor concentration, sleeping problems and demoralisation. Mild distress states, which do not interfere much with normal social functioning, can be considered to be part of normal daily life. However, severe distress states (as in NB) force a patient to give up and withdraw from major social roles, especially the occupational role. We conceptualize distress as the direct manifestation of the effort people must exert to maintain their psychosocial homeostasis and social functioning when confronted with taxing life stress [7]. The source of the stress may be anything that has the ability to threaten one's bio-psycho-social homeostasis (e.g. work load, conflicts, life events, traumatic experiences, psychosocial difficulties, grief, somatic disease, or psychiatric disorder).

Because distress symptoms virtually always accompany mood and anxiety disorders, it seems difficult to differentiate distress from depression and anxiety. However, when we try to separate distress from depression and anxiety, what is left must be the very core of these psychiatric disorders. When distress is separated from depression we are left with anhedonia and depressive thoughts. These symptoms are considered to represent the core symptomatology of major depression [8, 9]. When we separate distress from anxiety, we are left with irrational fears, anticipation anxiety and avoidance behaviour. These symptoms are characteristic of the various anxiety disorders [10]. Whereas distress is primarily a manifestation of a stress-coping problem, depression and anxiety are triggered or aggravated by still poorly understood dysfunctions of mood and anxiety regulation systems [11].

Somatization is a tendency to experience medically unexplained somatic symptoms, to attribute them to physical illness, and to seek medical help for them [12]. Various mechanisms may contribute to somatization, including sensitisation of the brain to bodily sensations [13], physiological abnormalities in the nervous and endocrine systems [14], heightened awareness of bodily sensations [15], and inappropriate illness beliefs and sickness behaviour [16]. Experiencing one or just a few medically unexplained symptoms (e.g. dizziness or upset stomach) is common in "normal" people under stressful circumstances [13, 17]. However, experiencing many unexplained symptoms from different organ systems (e.g. dizziness ánd upset stomach ánd palpitations ánd muscular aches) implies somatization as described above [16].

A non-specific general distress factor has been described in the literature before. However, there seems to be little consensus about the exact relationship between distress and anxiety/depression. Goldberg et al. described distress as a general factor of depression and anxiety, representing the overall severity of the disorder [18]. Dohrenwend et al. described a general distress factor as the common factor underlying many psychiatric screening lists [19]. Clark and Watson introduced the tripartite model in which general distress is viewed as a personality trait – "negative affectivity" – that is underlying depressive and anxiety disorders as a non-specific predisposition [20].

In our four-dimensional model of psychological symptoms, distress is not merely a (common) part of anxiety and depression but, instead, we see distress as a fourth dimension of psychopathology besides depression, anxiety and somatization. Distress is the most basic, most general, most "normal" expression of psychological problems. In principle, distress is independent from depression, anxiety and somatization. However, in practice, the dimensions are correlated, presumably because the strain that produces distress, may also trigger disturbances underlying depression, anxiety or somatization in vulnerable people.

Conceptually, as mentioned above, distress represents the most general expression of any psychological problem. Since a true valid and reliable gold standard for distress is not available, we adopted "any psychosocial diagnosis/reason for encounter" as established by the GP as the "criterion" for the 4DSQ Distress score. This criterion should represent a reasonable indicator of distress, with relevance for primary care. Given the unknown reliability of the criterion, any relationship with the 4DSQ Distress score can be interpreted as supporting validity of the 4DSQ Distress scale. In study A 2,127 consecutive primary care patients filled in a 4DSQ while the GPs recorded their diagnoses/reasons for encounter. These diagnoses/reasons for encounter were later categorised as either "psychosocial" or "somatic" by a researcher who was blinded for the 4DSQ scores. Examples of psychosocial diagnoses are "anxiety disorder", "sleeping problem", "nervousness", and "marriage problem". All diagnoses/reasons for encounter not overtly implying a psychosocial problem were coded as "somatic".

We considered the standardised psychiatric diagnosis of a current major depressive disorder as the "criterion" for the 4DSQ Depression score. In study D 55 GP patients with psychological symptoms were interviewed twice by their GP with an interval of 1–2 days. The diagnosis DSM-IV major depression was made using the Short Depression Interview (SDI) [22]. The patients filled in the 4DSQ at both occasions. In order to increase the power of the analysis, the measurements of both times were combined as if the retests were independent observations.

We adopted the standardised psychiatric diagnosis of a current anxiety disorder as the "criterion" for the 4DSQ Anxiety score. In study E 206 GP patients, selected because of a positive result of a screening test for anxiety, were interviewed by a mental health professional using the Structured Clinical Interview for DSM-IV (SCID) [23]. The patients filled in the 4DSQ.

We adopted the GP's suspicion of a psychosocial background in the case of a somatic diagnosis/reason for encounter as the "criterion" for the 4DSQ Somatization score. This criterion is not meant to be a true gold standard for somatization, but rather a reasonable indicator of somatization (i.e. the presentation of somatic complaints unexplained by physical illness), relevant for primary care. Given the unknown reliability of the criterion, any relationship with the 4DSQ Somatization score can be interpreted as supporting validity of the 4DSQ Somatization scale. In study A the GPs not only recorded their diagnoses/reasons for encounter, but they also rated the background of the diagnosis/reason for encounter on a 5-points somatic-psychosocial scale. Patients with a somatic diagnosis/reason for encounter were categorised into three groups according to the somatic-psychosocial score: "definite somatization" (score 4–5), "possible somatization" (score 2–3), and "no somatization" (score 1). We investigated the association between the 4DSQ scores and the GPs' suspicion of somatization in patients with a somatic diagnosis.

In study A the GP diagnosis was missing in 90 cases (4%). In 417 of the remaining 2,037 patients (20%) the GP recorded a psychosocial diagnosis/reason for encounter. The psychosocial and somatic groups differed significantly in all four dimensions of the 4DSQ (Table 4). The ROC analysis revealed that all four 4DSQ scales were associated with any psychosocial diagnosis/reason for encounter to some extent (Figure 1), but the Distress score yielded the highest AUC (0.79), being significantly higher than the AUCs of the Depression, Anxiety and Somatization scores (all p-values < 0.001). A Distress cut-off score of ≥ 11 had a sensitivity of 0.71 and a specificity of 0.72 for "detecting" any psychosocial diagnosis/reason for encounter. The final logistic regression model revealed that whether the GP made a psychosocial or a somatic diagnosis was mainly "predicted" by the Distress score (Table 5). With every increase of the Distress score by 1 point (the scale range is 32 points), the odds to receive a psychosocial diagnosis/reason for encounter increased by 13%.

In study D we had 102 instances with both a complete diagnostic assessment and complete results of the 4DSQ. The diagnosis major depression was established in 56%. The mean 4DSQ scores are shown in Table 6. The diagnosis major depression was associated with all four 4DSQ scales. The ROC curves for the 4DSQ scales detecting DSM-IV major depression are shown in Figure 2. The Depression score was the best discriminator between patients with and without a major depression, the AUC of the Depression score (0.83) being significantly larger than the AUCs of the Anxiety and Somatization scores (p-values 0.002 and 0.022 respectively). However, the Distress score performed almost as good, as the difference between the AUCs was not statistically significant (p = 0.555). The Depression score, using a cut-off of ≥ 6, had a sensitivity of 0.72 and a specificity of 0.80 for detecting major depression. Logistic regression analysis showed that the Depression score contributed the most to the prediction of major depression, but curiously, the Somatization score contributed a little to the prediction of major depression in addition (Table 7). For every increase of the Depression score by 1 point (the scale range is 12 points) the odds for having a major depression increased by 46%. Note that the Distress score did not have any additional value with respect to the prediction of major depression with the Depression score already in the equation.

Table 8 presents the anxiety disorder diagnoses established in study E. One-hundred-seven patients were diagnosed with one anxiety disorder; 72 patients with two or more anxiety disorders. Table 9 shows the mean scores for patients with no, one, and two or more anxiety disorders. Figure 3 shows the ROC curves of the 4DSQ scales to detect any anxiety disorder. The 4DSQ Anxiety scale outperformed the other 4DSQ scales marginally, but not significantly. The AUC of the Anxiety score (0.66) did not significantly differ from the AUCs of the Distress, Depression and Somatization scores (p-values 0.332, 0.490 and 0.401 respectively). A cut-off Anxiety score of ≥ 10 had a sensitivity of 0.62 and a specificity of 0.56. The logistic regression analysis revealed that in the final model only the Anxiety score was a significant predictor of any anxiety disorder, while the other 4DSQ scales did not add any predictive power (Table 10). For every increase of the Anxiety score by 1 point (the scale range is 24 points) the odds for having any (one or more) anxiety disorder(s) increased by 11%.

In study A 1,620 patients had a somatic diagnosis/reason for encounter. Of these patients 773 patients (48%) were suspected by their GP of definite (n = 256) or possible somatization (n = 517). Table 11 shows that all 4DSQ scores paralleled the GPs' level of somatization suspicion. The ROC analysis revealed that the Somatization score was the best discriminator between patients whose GPs suspected (possible or definitive) somatization and those whose GPs did not (Figure 4), the AUC of the Somatization score (0.65) being significantly larger than the AUCs of the Distress, Depression and Anxiety scores (all p-values < 0.001). A cut-off score of ≥ 7 had a sensitivity of 0.60 and a specificity of 0.62 for the GPs' suspicion of somatization in patients with a somatic diagnosis/reason for encounter. The logistic regression analysis revealed that the suspicion of a psychosocial background in patients with somatic symptoms (i.e. somatization) was primarily predicted by the Somatization score (Table 12). With every increase of the Somatization score by 1 point (the scale range is 32 points), the odds to have the GP suspect a (possible or definite) somatization increased by 10%. Furthermore, the Distress score added a little to the Somatization score in predicting the GPs' suspicion of definite somatization.

The notion that distress is the most general expression of psychological problems of any kind was confirmed by the Distress score, which showed substantial correlations with the scores of various other questionnaires measuring a range of symptoms from distress to depression and from anxiety to somatization. Furthermore, the Distress score was found to be associated with psychosocial stressors, and especially with psychosocial problems such as marital and financial problems and excessive occupational demands. These findings support the assumption that the Distress score is a non-specific indicator of any psychological problem. The Distress score was also shown to be the most important predictor of social dysfunctioning and sick leave. Of special interest is the association between the Distress score and any psychosocial diagnosis established by the GP. Considering that such diagnoses require consensus between GPs and patients on the psychosocial nature of the symptoms, it is plausible that distress plays a role in motivating patients to seek help and to discuss psychological issues with their doctor. Indeed, one of the practical applications of the 4DSQ in general practice is to increase patients' awareness of their distress, and to encourage their acknowledgement of psychological problems and their readiness to discuss these problems with their doctor.

The 4DSQ Depression scale was found to correlate with other depression scales, particularly with the BDI, which focuses on depressive cognitions [49]. After adjusting for the 4DSQ Distress score, the 4DSQ Depression scale showed little correlation with some other depression scales such as the HADS Depression scale and the SDS of Zung, which appeared to be more closely associated with the 4DSQ Distress score. These findings may indicate that the 4DSQ Depression scale measures more severe depressive disorders, whereas the Distress scale measures milder depressive disorders. Indeed, we found that the 4DSQ Depression and Distress scores performed almost equally well in detecting the whole range (from mild to severe) of DSM-IV major depressive disorders. However, the Distress score did not add any predictive power to the Depression score in the logistic regression analysis. Therefore, the 4DSQ Depression score seems to be sufficient to detect depressive disorders. Considering that the Depression score reflects the likelihood of the presence of a DSM-IV depressive disorder, we recommend two cut-off points in clinical practice: a relatively low cut-off point with high sensitivity to exclude a depressive disorder, and a relatively high cut-off point with high specificity to identify a high likelihood of depressive disorder. For the GP, a Depression score between the two cut-off points is a "prompt to consider" the presence of a depressive disorder [50]. Then, depending on the circumstances and the patient's history, the doctor might decide to wait and see, and to re-evaluate the patient a few weeks later, or to continue with a psychiatric diagnostic interview. However, a Depression score above the higher cut-off point is a "prompt to act" [50], i.e. to diagnose a depressive disorder without delay.

The 4DSQ Anxiety scale was found to correlate well with other scales that are used to measure anxiety, including the SCL Agoraphobia and Anxiety scales, the BAI, and the HADS Anxiety scale. However, one other anxiety scale, the STAI State scale, was not found to correlate much with the 4DSQ Anxiety scale, but appeared to correlate more with the Distress scale. On further consideration, the anxiety concept measured by the STAI State scale seems to be quite different from the anxiety concept measured by the other anxiety scales, in that it seems to be related to "normal" nervousness and lack of wellbeing (i.e. distress), as opposed to the kind of "abnormal" anxiety that is expressed in panic attacks and phobic anxiety. It is this "abnormal" anxiety, which is characteristic of anxiety disorders, that is measured by the 4DSQ Anxiety scale. Yet, we failed to demonstrate unequivocal criterion validity of the Anxiety scale with respect to standardised DSM-IV anxiety disorder diagnoses. In retrospect, we suspect that study E was not ideal for investigating the criterion validity of the Anxiety scale because the patients were highly selected (for anxiety), leaving little contrast between patients with and without an anxiety disorder. More research, with more heterogeneous study samples, is needed to establish the criterion validity of the 4DSQ Anxiety scale.

The 4DSQ Somatization scale was shown to measure exactly the same construct as the SCL Somatization scale (taking the reliability of both scales into account). Furthermore, we demonstrated criterion validity with respect to the GP's suspicion of somatization in patients with a somatic diagnosis/reason for encounter. Although the relatively low AUC (0.65) indicates that the Somatization score is not a perfect predictor of a GP's suspicion of somatization, the association between the score and the GP's assessment is interesting. Apparently, GPs recognise something that is expressed through an elevated Somatization score in a patient. It should be realised at this point that the GPs and patients probably were not able to discuss any psychosocial issues, because otherwise the GPs would have established a psychosocial diagnosis. Thus, the GP's assessment of the presence of a psychosocial background in patients with somatic symptoms must have been the result of a rather subjective process with questionable reliability. Assuming a relatively low reliability of our "criterion" for somatization, and considering that validity can never surpass reliability, an AUC-value of 0.65 may not be too bad at all. One of the practical applications of the 4DSQ in general practice is to obtain Somatization scores for patients who the GP suspects of having complaints with a psychological background. Discussing the 4DSQ scores with the patient provides valuable opportunities to address any psychosocial issues.

We found a special relationship between Distress, on the one hand, and Depression and Anxiety (and Somatization to a lesser extent) on the other hand: in most patients Distress seemed to underlie Depression and Anxiety (and Somatization to a lesser extent). To a large extent this peculiar relationship between the 4DSQ dimensions is responsible for the high correlations between Distress, on the one hand, and Depression, Anxiety and Somatization on the other hand. A low Distress score is highly predictive of the Depression and Anxiety scores (which must be low), but a high Distress score is minimally predictive of the Depression and Anxiety scores (which can be anywhere between low and high). This special relationship was also evident in the factorial structure of the 4DSQ scales. These findings support the use of the 4DSQ Distress scale as a screener for psychological problems of any kind in primary care.

It seems plausible to attach causal inferences to the relationships between the 4DSQ dimensions in accordance with our conceptual four-dimensional model [51]. Whenever individuals are confronted with the pressure of stress in their life or work, they start to experience distress because they have to put more effort into coping with the stressors, trying to maintain their normal level of social functioning. This is the most basic, most general, most "normal" response to stress. However, some of these people will also experience bodily symptoms (somatization) to some degree, due to a certain tendency [12]. Moreover, distress may act as a steppingstone to the development of a depressive and/or anxiety disorder in individuals with specific vulnerabilities. Of course, longitudinal studies are needed to confirm this interpretation of our cross-sectional data.