Language structure is influenced by the proportion of non-native speakers: A reply to Koplenig (2019)

A recent quantitative study claims language structure, whether quantified as morphological or information-theoretic complexity, to be unaffected by the proportion of those speaking the language non-natively [A. Koplenig, Royal Society Open Science, 6, 181274 (2019)]. This result hinges on either the use of a categorical notion of 'vehicularity' as a proxy for the proportion of L2 (second-language) speakers, or the imputation of an assumed zero proportion of L2 speakers for languages that are considered non-vehicular but for which no direct estimate of that proportion exists. We provide two alternative analyses of the same data. The first reanalysis treats uncertain non-vehicular languages as missing data points; the second one employs multiple imputation to fill in the missing data. Mixed effects models find a statistically significant negative relationship between proportion of L2 speakers and morphological complexity: in both reanalyses, a higher proportion of L2 speakers predicts lower morphological complexity. We find no statistically significant evidence for a relationship between proportion of L2 speakers and information-theoretic complexity, however.