Specifications can be about the psychometric properties of the test, or about technical issues, like a minimum number of items to be selected for a text passage or a graph. For an overview of various types of specifications, see Van der Linden (2005, chap. 2). Kingsbury e Zara (1998) proposed to stratify the item bank with respect to, for example, content classifications, and to rotate item selection over the various strata.