Depression is defined as the score on a depression scale. The higher the score, the more depressive an individual is. The score calculation is based on the 'Mental Health Inventory 5' or 'MHI-5', a test widely used internationally, consisting of 5 questions included in the written part of the 'Health’ module in the Integrated System of Social Surveys (POLS) conducted by Statistics Netherlands. The score on this scale appears to be closely related to feelings of depression.

The MHI-5 questions refer to a person’s feelings in the past 4 weeks. The questions are:
1. Did you feel very nervous?
2. Did you feel so dejected that nothing could cheer you up?
3. Did you feel calm and composed?
4. Did you feel depressed and gloomy?
5. Did you feel happy?
Each question has the following 6 response options: permanently-mostly-frequently-sometimes-seldom-never.

Figures are based upon the Integrated System of Social Surveys (POLS). As POLS is a sample survey, figures are subject to a margin of error. If data are monitored over a longer period (2001 up to and including 2008), the results will be more accurate.