Description of the studies from which the datasets have been used in this paper
Study A aimed to investigate the characteristics of patients with a nervous breakdown (NB) in general practice . Thirty-seven GPs handed out a questionnaire containing the 4DSQ to a random sample of 3,495 patients aged 15 to 64, and registered their diagnoses or reasons for encounter. The GPs recorded also their assessment of the somatic or psychological background of the consultation on a 5-point scale, from "exclusively somatic" (score 1) to "exclusively psychosocial" (score 5). The questionnaire was returned by 2,127 patients (response rate 61%).
From the respondents a stratified sample (n = 612) was selected for further investigation: all patients with a psychiatric diagnosis as registered by the GP (n = 85), all patients with a NB diagnosis (n = 141), and a sample of patients with psychological or somatic symptoms (n = 386). The follow-up study included a postal questionnaire, issued 1–2 weeks later, containing a checklist of psychosocial problems , a life events checklist, a neuroticism questionnaire , a 5-item social disability questionnaire, and a single question about current sick leave from work. The second questionnaire was returned by 458 patients after a mean interval between the questionnaires of 12.0 days (SD 5.5).
Study B was part of an occupational health survey . All employees of a telecom company (n = 7,522) received a questionnaire containing the 4DSQ, a job stress questionnaire, the Job Content Questionnaire (JCQ) , and a mastery questionnaire, the Pearlin Mastery Scale . The questionnaire was returned by 3,852 employees (response rate 51%).
Study C was designed to investigate an occupational health care intervention for employees who were on sick leave because of an adjustment disorder . There had to be a recent identifiable stressor and the patient had to have at least 8 out of 17 distress symptoms. Patients were excluded if one of the DSM-IV exclusion criteria for adjustment disorder held (e.g. the patient had a major depression). The physicians included 280 patients. The baseline assessment included the 4DSQ, the Symptom Checklist (SCL-90) [31, 32], as well as the Pearlin Mastery Scale .
Study D was designed to investigate the reliability and validity of the Short Depression Interview (SDI) to assess depressive symptoms and to diagnose major depression . Fourteen GPs selected 55 patients (aged 15 years and older) with a psychological problem of any kind, and at least 3 out of the following 6 symptoms: fatigue, sleeping problems, nervousness, irritability, feeling depressed, feeling anxious. The GPs interviewed the patients twice, a few days apart. After the first interview, the patients filled in the 4DSQ, the Self-rating Depression Scale of Zung (SDS) [35, 36] and the General Health Questionnaire (GHQ) [27, 28]. After the second interview, the patients filled in the 4DSQ, the Hospital Anxiety and Depression Scale (HADS) [33, 34] and the Maastricht Questionnaire (MQ) , which assessed "vital exhaustion" . According to the SDI more than half of the patients fulfilled criteria of DSM-IV major depression.
Study E was designed to compare the effectiveness of three interventions for panic disorder and generalised anxiety disorder in primary care patients . Forty-six GPs identified 258 adult patients, aged 18 years and older, who scored 5 or more on the Short and Simple Screening Interview . Reasons for exclusion were: the presence of an organic mental disorder, mental retardation or a psychotic disorder, treatment of an anxiety disorder in the recent past, use of antidepressants or the use of a benzodiazepine in daily doses of more than 30 mg oxazepam equivalents. The patients were given the 4DSQ and a clinical assessment by a mental health professional using the Structured Clinical Interview for DSM-IV (SCID) . Two-hundred-and-thirty-seven patients completed the 4DSQ; 206 of them completed the SCID interview as well. According to this interview, 87% of the patients fulfilled criteria of one or more DSM-IV anxiety disorders.
Study F was designed to investigate the effectiveness of an antidepressant in primary care patients with minor or mild-major depression. Fifty-three GPs included 181 patients, aged 18 years and older, with 3 to 6 depressive symptoms mentioned in the DSM-IV criteria for major depression. Patients with severe suicidal behaviour, addiction, apparent cognitive decline (dementia), or psychotic symptoms, were excluded. At baseline, the patients filled in the 4DSQ, the Beck Depression Inventory (BDI) [37, 38], the Beck Anxiety Inventory (BAI) , the NEO-FFI Neuroticism scale [46, 56], and the Short Form Health Survey (SF-36) [57, 58]. Three patients did not fill in the questionnaires.
Study G was a parallel study of study A. Nineteen primary care based social workers handed out the 4DSQ to a sample of their clients (n = 83). Seventy-seven clients returned the questionnaire (response rate 93%). All respondents filled in the second questionnaire inquiring after psychosocial problems, life events, neuroticism, social disability, and sick leave, after a mean interval of 8.3 (SD 9.8) days.
Study H was designed to test the reliability and validity of the 4DSQ in physiotherapy patients . Twenty-three primary care based physiotherapists handed out the 4DSQ and the State-Trait Anxiety Inventory (STAI) [40, 41] to a consecutive sample of new patients. The questionnaires were returned by 382 patients.
Study I aimed to assess stability and change of the 4DSQ in general practice patients over a 1–2 week period. Five GPs handed out the 4DSQ to 98 patients with various psychological problems. The questionnaire was returned by 86 patients (response rate 88%). One week later, a second 4DSQ was sent to these patients (response: n = 66, response rate 77%). The second 4DSQ was accompanied by one question about the patients' perception of stability/change in their symptoms. This global impression (GI) question had 5 response options: "improved definitely" (score 1), "improved somewhat" (score 2), "unchanged" (score 3), "deteriorated somewhat" (score 4), and "deteriorated definitely" (score 5).
Study J aimed to estimate the amount of time it takes for general practice patients to fill in the 4DSQ. In one general practice (5 GPs) two extra questions were added temporarily to the 4DSQ that was used routinely in the practice. The questionnaire was filled in by 129 patients.