6.2 Fixed instrument
Preparing a fixed instrument has some additional and different considerations compared with preparing an adaptive test. Fixed instrument are often consisting of separate age-forms, with different and overlapping items in each age-form. Depending on how wide the age-band is, the children within the age-group may differ more or less. This should all be considered with selecting the items and especially with assigning items to age-forms. For face-validity the domain representation in each age-form can be checked separately. And additionally the reliability of the instrument can be checked as well.