• anxiety disorders;
  • depressive disorder;
  • reference values;
  • routine outcome monitoring;
  • instruments;
  • somatoform disorder


Rationale, aims and objectives:  Routine outcome monitoring (ROM) was developed to establish the outcome of psychotherapeutic and pharmacological treatments through repeated assessments before, during and after treatment. Although standardization of psychiatric assessments and their reference values are essential for patient care, for various ROM instruments reference values are not available. The aim of the Leiden ROM Study is to generate reference values for 22 ROM instruments, covering generic and specific mood, anxiety and somatoform (MAS) disorders, for the general population. This article describes the extensive process of recruitment, as well as baseline characteristics of patient versus non-patient groups.

Method:  Cross-sectional study in randomly selected participants aged 18–65 years from the Dutch population, included through general practitioners.

Results:  Extensive demographic, psychosocial, mental health, and biological data from 1302 participants, recruited via general practitioners, were collected during a two-hour standardized assessment including observer-rated and self-report scales. These data will be compared with corresponding data from 7840 patients with psychopathology who were referred to secondary care. On-going quality control and calibration ensured maintenance of high quality during data collection.

Conclusions:  This reference group study for mental health assessments is the first study of this size carried out in the Netherlands. The results of this study are expected to be of value to secondary psychiatric care because they allow the indication of progress in health, treatment effect and possible termination of treatment. Additionally, the reference values can be used by primary care physicians as decision threshold for referral to specialized mental health care and vice versa.