Endless Loops: Psychometrical foundations of the item type EP [Endlosschleifen: Psychometrische Grundlagen des Aufgabentyps EP]

This paper describes the theory-based construction of the item-type E P (photographic endless loops) as a consecutive three-stage-process consisting of three studies showing the - often arduous - way of obtaining Rasch homogeneity for an item set. In study 1 (n = 324), the origin, the constructive foundations as well as first results are reported. Study 2 (n = 378) marks an important transition in the developmental process as Rasch homogeneity is achieved; in addition new findings about the item generation rules are obtained. Study 3 acts as a validation study confirming the unidimensionality of the item set used in study 2. On the ground of established Rasch homogeneity the theory-led scale construction principle is discussed as a prototypical way of successfully applying the Rasch model for the purpose of scale construction. Content-based considerations concerning the investigated item type and confirmed through preliminary research studies mark the end of the discussion Looking ahead, the developmental potential of the endless loops is pointed out.