Figure 1.

Flowchart of patient recruitment and selection. Note that the total number of General Practitioners addressed is a combination of the GPs extracted from the database when the first letter was sent and the new and changed records of the database at the time point the second letter was sent. In the end, in total, only 42 filled-out questionnaires were received, note that 10 GPs did not return the questionnaire (i.e. because of lack of time).