This contribution explores a methodological problem in language acquisition studies. Much research in language acquisition has shown that children use statistical learning as a strategy in the acquisition of their native language (Saffran et al. 1996 and many others). Frequency of occurrence is also believed to determine the order of acquisition of phonological structures in the construction of the grammar (Boersma and Levelt 2000, Levelt et al. 2000, van de Weijer and Sloos 2013). How do we obtain the relevant frequency information for acquisition studies?
Ideally, we should take into account children's speech or child-directed speech (CDS), depending on the purposes of the investigation. Investigations into the construction of the lexicon and acquisition of the grammar depend on the input, the perception, and the lexical storage of the child, and therefore, frequency data on CDS seem most desirable.