“In sum, there is no evidence that the development of function words is best explained from a linear or discontinuous point of view. […] The non-linear fitting has implications for the study of language development. […] It does not mean that age averages are wrong.
However, one must be careful with respect to certain claims about development. Group data do not yield a solid description of (individual) development. Only age dependent development (i.e. strictly timed development) will benefit from such averages. The second point to be made is that whatever the averages, in all cases the data are best modelled by a non-linear fit.”
From: Going the distance: A Non-Linear Approach To Change In Language Development / H.G. Ruhland. Groningen, 1998.
© Rick Ruhland 2018