Reference values for major depression questionnaires: the Leiden Routine Outcome Monitoring Study

Background: The Beck Depression Inventory-II (BDI-II), the Inventory of Depressive Symptoms (self-report) (IDS-SR) and the Montgomery-Äsberg Depression Rating Scale (MADRS) are questionnaires that assess symptom severity in patients with a depressive disorder, often part of Routine Outcome Monitoring (ROM). We aimed to generate reference values for both "healthy" and "clinically depressed" populations.

Methods: We included 1295 subjects from the general population (ROM reference-group) recruited through general practitioners, and 4627 psychiatric outpatients diagnosed with Major Depressive Disorder (MDD) or dysthymia (ROM patient-group). The outermost 5% of observations were used to define limits for one-sided reference intervals (95th percentiles; P95). Receiver Operating Characteristics (ROC) analyses were used to yield alternative cut-off values. Internal consistency was assessed.

Results: The mean age was 40.3yr (SD=12.6) and 39.3 (SD=12.3) for the ROM reference and patient-groups, respectively, and 62.8% versus 61.0% were female. Cut-off (P95) values differed for women and men, being respectively 15 and 12 for the BDI-II, 23 and 18 for the IDS-SR, and 12.5 and 9 for the MADRS. ROC analyses yielded almost equal reference values. The discriminative power of the BDI-II, IDS-SR and MADRS scores was very high. Internal consistency was excellent for total scores and satisfactory for all subscales, except for the IDS-SR subscale Atypical Characteristics.

Limitations: Substantial non-response and limited generalizability.

Conclusions: For the BDI-II, IDS-SR and MADRS a comprehensive set of reference values were provided. Reference values were higher in women than in men, implying the use of sex-specific cut-off values. Either instrument can be offered to every patient with MAS disorders to make responsible decisions about continuing, changing or terminating therapy.