This article explores the effect that words from different lexical categories have on disfluency in Persian children who stutter. The authors reported content and content–function words were significantly more likely to show stuttering-like dysfluencies than function words.
Vahab, Maryam, Zandlyan, Azabeh, Hadi kFalahi, Mohammad, and Howell, Peter. (2013). Lexical category influences in Persian children who stutter. Clinical Linguistics & Phonetics. doi:10.3109/02699206.2013.809792