Chapter Second

Abstract

An important notion that needs to be introduced in support of the plea for an evaluation of ontology in the previous chapter is the difference between the stability of a performance and its accuracy. Although performance may be accurate, for example, a word is read aloud correctly on a reading test, a distinction can and should be made between stable, proficient, coordinated performance and unstable performance leading to that response (see Farrar & Van Orden, 2001; Van Orden, Kloos, & Wallot, 2009; Wijnants, Bosman, Hasselman, Cox, & Van Orden, 2009). The analogy of a path may be useful here: Some paths are easily traversed and get you straight to where you want be (the correct answer), other paths will get you there as well, but may take more time or more effort. In a similar fashion different paths may lead to erroneous answers as well. Exactly which path will be traversed is dependent on the context in which someone is asked to choose a path in the first place. In the context of psychological measurements, the one being asked to choose a path, that is, the participant is a context as well. A theory about both proficient and impaired performance pertaining to a skill like reading should take into account the fact that a scientific theory only makes definite predictions relative to well-­‐defined measurement contexts (see Box 1.1). Such a theory of measurement is not readily available in psychological science as it is in the physical sciences (see e.g., Cox, Hasselman, & Seevinck, 2011). Therefore, in the present chapter we will focus on a detailed task analysis of variables that are hypothesized to be causally related by the speech perception deficit hypotheses of developmental dyslexia. This analysis will show just how well such contexts need to be defined.