The authors reported that this study revealed that anxiety may not always be related to overt indicators of stuttering. The authors concluded that traditional procedures for assigning severity ratings to individuals, who stutter based on percent syllables stuttered and the Stuttering Severity Instrument are not significantly related to psychological processes central to the stuttering experience.
Manning, Walter & Beck, J. Gayle. (2013). The role of psychological processes in estimates of stuttering severity. Journal of Fluency Disorders. http://dx.doi.org/10.1016/j.jfludis.2013.08.002