Noun distribution in natural languages

Previous research on word class distribution claimed that 37% of word tokens are nouns, suggesting that there might exist a certain regularity of noun proportion among human languages. To explore this possibility, we examined the proportion of noun and four other word classes within British and American English, and across seven languages in terms of different word frequency band. Results indicated that the noun proportion is evidently about or larger than 37%, and meanwhile increases with word rarity. Among frequent words, nouns increase as minor word classes decrease, whereas among rare words, the noun proportion remains a stable level.