Reference values for generic instruments used in routine outcome monitoring: the leiden routine outcome monitoring study

INTRODUCTION The Brief Symptom Inventory (BSI), Mood & Anxiety Symptom Questionnaire -30 (MASQ-D30), Short Form Health Survey 36 (SF-36), and Dimensional Assessment of Personality Pathology-Short Form (DAPP-SF) are generic instruments that can be used in Routine Outcome Monitoring (ROM) of patients with common mental disorders. We aimed to generate reference values usually encountered in 'healthy' and 'psychiatrically ill' populations to facilitate correct interpretation of ROM results. METHODS We included the following specific reference populations: 1294 subjects from the general population (ROM reference group) recruited through general practitioners, and 5269 psychiatric outpatients diagnosed with mood, anxiety, or somatoform (MAS) disorders (ROM patient group). The outermost 5% of observations were used to define limits for one-sided reference intervals (95th percentiles for BSI, MASQ-D30 and DAPP-SF, and 5th percentiles for SF-36 subscales). Internal consistency and Receiver Operating Characteristics (ROC) analyses were performed. RESULTS Mean age for the ROM reference group was 40.3 years (SD=12.6) and 37.7 years (SD=12.0) for the ROM patient group. The proportion of females was 62.8% and 64.6%, respectively. The mean for cut-off values of healthy individuals was 0.82 for the BSI subscales, 23 for the three MASQ-D30 subscales, 45 for the SF-36 subscales, and 3.1 for the DAPP-SF subscales. Discriminative power of the BSI, MASQ-D30 and SF-36 was good, but it was poor for the DAPP-SF. For all instruments, the internal consistency of the subscales ranged from adequate to excellent. DISCUSSION AND CONCLUSION Reference values for the clinical interpretation were provided for the BSI, MASQ-D30, SF-36, and DAPP-SF. Clinical information aided by ROM data may represent the best means to appraise the clinical state of psychiatric outpatients.