[A new instrument to measure clinical outcomes]

De Haan et al. have developed a new disability score (Amsterdam linear disability score; ALDS) based on item response theory. The advantages of the instrument are its generic applicability for multiple disease categories of varying severity and its linear scaling as a continuous variable, which facilitates interpretation and requires smaller sample sizes. Moreover, such a tool may very well be used as complementary outcome measure in a subset of patients participating in a mega-trial that concentrates on simple outcomes. A limitation is that users of the score still need to become familiar with its interpretation. It is not yet clear how many questions are needed to obtain a reliable estimate of the ALDS and therefore the time needed to complete the instrument is still uncertain.