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

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.

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.

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.

Substantial non-response and limited generalizability.

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.