Construction of a Danish CDI short form for language screening at the age of 36 months: methodological considerations and results.

Several research groups have previously constructed short forms of the MacArthur-Bates Communicative Development Inventories (CDI) for different languages. We consider the specific aim of constructing such a short form to be used for language screening in a specific age group. We present a novel strategy for the construction, which is applicable if results from a population-based study using the CDI long form are available for this age group. The basic approach is to select items in a manner implying a left-skewed distribution of the summary score and hence a reliable discrimination among children in the lower end of the distribution despite the measurement error of the instrument. We report on the application of the strategy in constructing a Danish CDI short form and present some results illustrating the validity of the short form. Finally we discuss the choice of the most appropriate age for language screening based on a vocabulary score.