Natke, U., Sandrieser, P., Ark, M. van, Pietrowsky, R., & Kalveram, K. Th. (2004) Linguistic stress, within-word position, and grammatical class in relation to early childhood stuttering. Journal of Fluency Disorders, 29 (2), 109-122.

Abstract
The purpose of the present study was to investigate whether the link that has been established between stuttering and linguistic stress in adolescents and adults (the so-called stress effect) can also be observed in childhood stuttering. To account for confounding variables, both within-word position and grammatical class were measured, because these factors covary with linguistic stress. Speech samples of twenty-two preschool children (mean time of 9 months since onset of stuttering) were analyzed. The relative stress of each syllable was rated and syllables were categorized into long and short stressed, unstressed and intermediately stressed syllables. Results showed that 98 % of stuttering events occurred on first syllables of words, i.e. a clear word-initial effect. Stuttering frequency on first syllables of function words was 16.9 % and significantly higher than the frequency of stuttered first syllables of content words (11.5 %). In function words short stressed syllables and intermediately stressed syllables were stuttered more often than unstressed syllables. The analysis for individual disfluency types revealed that, for function words, stuttering on short stressed syllables was associated with prolongations and syllable repetitions. However, in intermediately stressed syllables stuttering coincided most often with one-syllable word repetitions. This differentiation of the stress effect may suggest different causal mechanisms underlying these disfluency types.