Natke, U., Sandrieser, P., Pietrowsky, R., & Kalveram, K. Th. (2006) Disfluency data of german preschool children who stutter and comparison children. Journal of Fluency Disorders, 31 (3), 165-176.

Abstract
This study compared the disfluencies of German-speaking preschool children who stutter (CWS, N= 24) with those produced by age- and sex-matched comparison children who do not stutter (CWNS, N= 24). In accordance with Yairi and Ambrose’s [Yairi, E., & Ambrose, N. (1992). A longitudinal study of stuttering in children: A preliminary report. Journal of Speech and Hearing Research, 35, 755-760] guidelines the CWS group had a narrow age range (2-5 years) and were seen close to the reported time of their stuttering onset (average of 8 months). Furthermore, over 95% of the CWS group had not received any type of speech therapy intervention. Consistent with previous findings for English-speaking preschool children, ‘stuttering-like’ disfluencies (prolongations, blocks, part- and one-syllable word repetitions) were significantly more frequent in CWS (mean = 9.2%) than in CWNS (mean = 1.2%), whereas no significant group differences occurred with respect to ‘normal’ disfluencies. The number of iterations in stuttering-like disfluencies was also significantly higher in CWS (mean = 1.28 iterations) than in CWNS (mean = 1.09 iterations). In contrast to previous findings, a sub-group of children who have been stuttering for a shorter time (1-5 months) did not differ from a sub-group who had stuttered for a longer period (8-22 months).