Compared with other methods of psychological assessment, the observation of behaviour shows some advantages, especially when standardised rating scales are used. Such a scale is developed for use in psychogeriatric nursing homes, geriatric wards of psychiatric hospitals and daycare units: the Gedragsobservatieschaal voor de Intramurale Psychogeriatrie (GIP). Scales that already existed were too limited or tested insufficiently. Rasch analyses are used to develop fourteen separate subscales of the GIP.