Incidence of CAS refers to the number of new cases identified in a specified time period. Prevalence of CAS refers to the number of people who are living with the condition in a given time period. Efforts to determine epidemiologically sound estimates of the incidence and prevalence of CAS have been hindered by a number of factors, including a lack of clear and consistent diagnostic guidelines (Shriberg, Aram, & Kwiatkowski, 1997) and adequately validated diagnostic tools (McCauley & Strand, 2008). These same factors may also play a role in the frequent overidentification of CAS by clinicians (Davis, Jakielski, & Marquardt, 1998; Shriberg & McSweeney, 2002).
A population estimate based on clinical referral data suggests that CAS occurs in 1-2 children per 1,000 (0.1%-0.2%; Shriberg et al., 1997) and is found in 3.4%-4.3% of the children referred for speech disorders (Delaney & Kent, 2004). On average, idiopathic CAS affects more boys than girls by a ratio of 2 or 3:1 (Hall, Jordan, & Robin, 1993; Lewis, Freebairn, Hansen, Taylor et al., 2004). Higher prevalence rates have also been reported with certain medical conditions, such as galactosemia and fragile X syndrome (Shriberg, Potter, & Strand, 2011; Spinelli, Rocha, Giacheti, & Richieri-Costa, 1995).