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Purpose The goals of the present study were to investigate whether (1) the speech disfluencies of preschool-age children are normally distributed; (2) preschool-age children who do (CWS) and do not stutter (CWNS) differ in terms of non-stuttered disfluencies; (3) age, gender, and speech-language ability affect the number and type of disfluencies children produce; and (4) parents’ expressed concern that their child stutters is associated with examiners’ judgments of stuttered disfluency. Method Four hundred and seventy two children participated, of which 228 were CWS (56 girls), and 244 CWNS (119 girls). Participants provided conversational speech samples that were analyzed for frequency of occurrence of (a) stuttered disfluencies, (b) non-stuttered disfluencies, and (c) total disfluencies. Results Results indicated that the underlying distributions of preschool-age children's stuttered and non-stuttered disfluency counts followed a negative binomial distribution (i.e., were not normal), with more children “piling up” at the low end [none or few disfluencies] and fewer children scoring in the upper [more severe stuttering] end of the distribution. Findings also indicated that non-stuttered disfluencies significantly predicted CWS/CWNS talker group classification, information that may be helpful to augment, but not supplant, talker group classification criteria based on stuttered disfluencies. Moreover, expressed parental concern about stuttering was strongly associated with frequency of stuttered disfluencies. Conclusion Findings suggest that the entirety of preschool-age CWS’ speech disfluencies – non-stuttered as well as stuttered – differs from that of their CWNS peers and that because these disfluencies are not normally distributed statistical analyses assuming normality of distribution are not the most appropriate means to assess these differences. In addition, certain “third-order” variables (e.g., gender) appear to impact frequency of children's disfluencies and expressed parental concerns about stuttering are meaningfully related to examiners’ judgments of stuttered disfluencies. Learning outcomes: The reader will recognize differences in speech disfluencies of preschool-age children who do and do not stutter. The reader will recognize whether age, gender and speech-language ability affect the number and type of disfluencies children produce. The reader will describe whether parental concern about stuttering is associated with examiners’ judgments of stuttering.

During the late 1950s, Johnson et al. (1959) provided normative data regarding the speech disfluencies of children who do and do not stutter. These researchers obtained their data from assessments of audio recordings of children's speech disfluencies. Since then, several others based on similar recordings of speakers of English (e.g., Ambrose and Yairi, 1999, Pellowski and Conture, 2002 and Yaruss et al., 1998a) and speakers of other languages (e.g., Boey et al., 2007, Carlo and Watson, 2003, Martins and Andrade, 2008 and Natke et al., 2006), have contributed data to the foundation laid down by Johnson and colleagues in the 1950s. Combined, these empirical investigations, studied 908 children who stutter (CWS) and 258 children who do not stutter (CWNS). Although the nature of the samples differed (e.g., some involved the child talking to an experimenter, others the child talking to a caregiver, and some collected the data within research whereas others within a clinical setting), this accumulated dataset represents one of the largest repositories of information presently available regarding the speech disfluencies of CWS and CWNS. There are, however, some issues relating to this body of knowledge that bear further consideration. First, there is the issue of how underlying characteristics of stuttered (i.e., sound-syllable and monosyllabic whole-word repetitions and sound prolongations) and non-stuttered (i.e., interjections, phrase repetitions and revisions) disfluencies may impact data analysis. For example, are the distributions of such disfluencies Gaussian or normal? Second, is the issue of whether, in addition to stuttered disfluencies, “non-stuttered,” “other” or “normal” disfluencies are salient to our understanding and/or classification of developmental stuttering in preschool-age children. Third, is the issue of misattribution of effect, that is, do third-order variables (e.g., age, gender or speech-language status) confound our understanding of between-group differences in speech disfluency. Fourth, is the issue of whether there is an association between parents/caregivers’ expressed reports of concern that their child is or is suspected to be stuttering and examiners’ measurement of the child's instances of stuttered disfluencies? Below, we briefly examine each of these issues. The first issue, the distribution of speech disfluencies, has received little attention in data analyses, with a few exceptions. For example, Johnson, Darley, and Spriestersbach (1963) noted that the frequency distributions of speech disfluencies “are considerably skewed or “long-tailed in one direction” with “piling up of scores toward the low end of the distribution” (p. 252). Similar descriptions were also reported by Davis (1939) and Jones, Onslow, Packman, and Gebski (2006). Johnson and colleagues further speculated that from such distributions “we may draw the generalization that there are more relatively mild than relatively severe stutterers” (p. 252). Interestingly, however, researchers assessing between-group differences in speech fluency (e.g., Yaruss et al., 1998a and Yaruss et al., 1998b) have typically employed parametric inferential statistical analyses that assume normality of distribution (e.g., analysis of variance, t-tests, etc.). Unfortunately, despite the observations of Johnson and colleagues, as well as Davis and others, there is little empirical evidence in the literature that the underlying distributions of reported speech disfluencies (e.g., stuttered disfluencies, non-stuttered disfluencies and so forth) are normally distributed. If the distributions of (non)stuttered disfluencies assume a non-normal or non-Gaussian form (e.g., strong positive skew), then the use of parametric inferential statistics may be problematic. If the assumption of normality cannot be met, then the assumption of ordinary least squares regression or analysis of variance is violated, possibly leading to the rejection of the null hypothesis when in fact it is true. If such violation is the case, it leads to the suggestion that researchers’ consider employing analytical statistical models that better fit the data's actual distribution. A second question concerns the frequency of stuttered disfluencies and non-stuttered or normal disfluencies exhibited by children who do and do not stutter. Many studies of developmental stuttering, and reasonably so, have classified the two talker groups based on frequency of instances of “stuttering” (e.g., Ambrose & Yairi, 1999; Anderson & Conture, 2001; Logan and LaSalle, 1999, Sawyer and Yairi, 2006 and Watkins and Yairi, 1997). It should be noted that that some differences do exist across various studies in the way stuttered disfluencies are described as well as what constitutes a stuttered disfluency (for further review, see Einarsdottir & Ingham, 2005). At present, however, some have classified children as stuttering if the child exhibits 3% or greater stuttered disfluencies in their conversational speech sample (e.g., Conture, 2001 and Yairi and Ambrose, 2005). Similarly, Boey et al. (2007), based on a large sample of Dutch-speaking children (n = 772), reported that the “3% rule” has high specificity (true negative CWNS classifications) and high sensitivity (true positive CWS classifications). However, to the present writers’ knowledge, specificity and sensitivity of the “3% rule” have never been assessed in a large sample of English-speaking children. Although frequency of stuttered disfluencies is often used to diagnose and classify stuttering in children, there is less certainty regarding the salience of “non-stuttered,” “other,” or “normal” disfluencies to the diagnosis and/or understanding of developmental stuttering. Some studies have reported that CWS produce significantly more non-stuttered disfluencies than CWNS (Ambrose and Yairi, 1999, Johnson et al., 1959 and Yairi and Ambrose, 2005) whereas others did not find any significant difference (Logan, 2003; Pellowski and Conture, 2002 and Yairi and Lewis, 1984). One may ask, therefore, whether non-stuttered speech disfluencies of CWS objectively differentiate the two talker groups. If they do differentiate the two talker groups, it would suggest that the entirety of CWS's speech disfluencies, not just the stuttered aspects, differ from typically developing children, at least in terms of frequency of occurrence. Certainly, previous empirical findings indicate that CWS produce non-stuttered disfluencies; however, these findings are seldom discussed in detail (cf. Ambrose and Yairi, 1999 and Pellowski and Conture, 2002). Some authors have also suggested that frequency of total disfluencies (i.e., stuttered plus non-stuttered) provides a reasonable criterion for talker group classification (Adams, 1977). Although the use of total disfluency as criterion for talker-group classification does bring non-stuttered disfluencies under the tent of decisions involved with talker group (CWS vs. CWNS) classification criteria, this criterion is confounded by its inclusion of stuttered disfluencies, the latter shown to significantly distinguish between children who do and do not stutter (e.g., Boey et al., 2007). Nevertheless, Adams’ suggestion highlights the possibility that measures besides instances of stuttered disfluency may have diagnostic salience. This possibility raises the question of whether non-stuttered speech disfluencies may augment clinicians’ as well as researchers’ attempts to develop a data-based diagnosis of developmental stuttering. A third issue is the potential misattribution of effect. Specifically, when studying possible differences between CWS and CWNS on a particular variable (e.g., frequency of disfluencies during conversational speech), other possible predictors co-exist, for example, age, gender, or expressive language abilities. Researchers have often dealt with this issue by matching the two talker groups (i.e., CWS and. CWNS) for age, gender, speech-language abilities, etc. before assessing between-group differences in speech fluency. However, this matching procedure does not necessarily indicate whether, for example, a variable such as chronological age impacts the actual reported between-group (i.e., CWS vs. CWNS) differences in frequency of speech disfluencies, stuttered or otherwise. One way to address this issue is to statistically model potentially confounding variables as covariates. This model-based approach has an advantage over matching talker groups for possible confounds (e.g., age) because it (a) allows the experimenter to obtain representative samples of both talker groups more closely reflective of the natural variation in these variables and, more importantly, and (b) assess whether such variables (e.g., gender) actually impact reported between-group differences in speech disfluencies. In the present study, and based on review of empirical studies of speech disfluencies in young children, we selected three variables commonly matched or considered when assessing between-group differences: age, gender, and speech-language abilities. These three variables were covariates in our statistical models/data analyses of preschool-age children's speech disfluencies. Certainly, these are not the only possible covariates, but they are three of the most common variables investigators have reported considering when assessing group differences between preschool-age CWS and CWNS. Immediately below we briefly review the possible association of each of these three variables and childhood stuttering. Regarding the chronological age of preschool-age CWS, it should be noted that most if not all standardized speech-language tests are age-normed. Further, experience with stuttering (i.e., time since onset) in young children is intimately connected to chronological age (e.g., Pellowski & Conture, 2002), with some tests used to assess childhood stuttering, for example, the KiddyCAT, apparently being sensitive to chronological age (e.g., Clark, Conture, Frankel, & Walden, 2012). Indeed, frequency of different disfluency types may vary with age and differ between young and older children (e.g., Davis, 1939, DeJoy and Gregory, 1985 and Yairi and Clifton, 1972). Whether chronological age impacts between-group differences in stuttered and non-stuttered disfluencies remains an open empirical question. With regard to the gender of preschool-age CWS, there is considerable evidence that the prevalence of stuttering is greater in males than females (e.g., Bloodstein & Bernstein Ratner, 2008), and that males are also more at risk for persistence (Yairi & Ambrose, 1992; Yairi and Ambrose, 2005 and Yairi et al., 1996). In view of this gender difference among CWS, it seems important to better understand whether gender impacts between-group differences in stuttered and non-stuttered disfluencies, as well as within-group differences. Based on their findings, Johnson et al. (1959) suggest that gender does not impact these between- and within-group differences, but to the present authors’ knowledge this issue has not been empirically replicated, especially with large samples of both preschool-age CWS and their CWNS peers. It is known that speech and language abilities develop with age and that stuttering for many children begins during the time of rapid language growth between the 2.5 and 5 years of age (e.g., Bloodstein & Bernstein Ratner, 2008). Furthermore, there is some evidence of between group-differences (CWS vs. CWNS) in articulation and/or phonological disorder (e.g., Blood, Ridenour, Qualls, & Hammer, 2003; cf. Clark et al., 2013). Likewise, meta-analytical findings suggested that CWS scored significantly lower than CWNS on norm-referenced measures of overall language as well as receptive and expressive vocabulary (Ntourou, Conture, & Lipsey, 2011). Furthermore, preschool-age CWS’ tendency to stutter on utterance-initial words increases with sentence length, a finding suggesting that language/linguistic processes contribute to the frequency/locus of stuttering (Richels, Buhr, Conture, & Ntourou, 2010). Indeed, language growth and complexity appears to be associated with children's speech disfluency (e.g., Yaruss, Newman, & Flora, 1999). It has also been shown that children with histories of specific expressive language impairment are significantly more disfluent than their peers with normal language development (Boscolo et al., 2002 and Hall et al., 1993; cf. Nippold, 2012). It is not clear, however, whether speech and language abilities, as well as age, affect frequency and type of disfluencies in typically developing children who do and do not stutter. A fourth issue is the association parents/caregivers’ expressed concern that their child is or is suspected to be stuttering and examiners’ judgment of frequency of children's stuttered disfluencies. While both measures involve perceptual judgments and are, to greater or lesser degrees, somewhat subjective, examiner judgment is often considered relatively objective and parental concern, while certainly a reality with regard to childhood stuttering, seemingly less so (although some, for example, Yairi & Ambrose, 2005, have used an ordinal scale for parents to judge their level of concern). However, to the present writers’ understanding, there has been little attempt to empirically assess the nature of the association between parents’ expressed concern and examiners’ judgment of stuttered disfluencies. Although it might be assumed that some degree of association exists, this remains an open empirical question. Knowing that these two variables – examiners judgment of stuttering and parental expressed concern about their child's stuttering – are associated would seem to lend a degree of demonstrated concurrent validity to both measures, something that appears presently lacking. Overall, some basic variables associated with early childhood speech disfluencies (i.e., distribution of stuttered and non-stuttered disfluencies), as well as the impact of related variables on such disfluencies have received relatively little empirical attention. As a result, our understanding of salient variables associated with preschool-age children's speech fluency is less than comprehensive. Without such understanding, we would seem to be less than aware of how these variables impact our assessment of children's speech disfluencies and/or the diagnosis of childhood stuttering. Therefore, the present study addressed these issues by examining childhood disfluencies in a large (n = 472) sample of preschool-age children. These data were collected in a consistent manner using a standard battery of testing procedures and measures commonly used by practicing clinicians as well as researchers who study childhood stuttering. To assess preschool-age CWS and CWNS's speech disfluencies, four questions were investigated. The first question asked whether the stuttered, non-stuttered and total speech disfluencies of preschool-age children who stutter are normally distributed (a question essential to the selection of analytic statistical models). It was hypothesized that preschool-age children's speech disfluencies are not normally distributed, rather that they are positively skewed with more children “piling up” at the low end of the distribution (none or few disfluencies) and fewer children scoring in the upper (more severe stuttering) end of the distribution. The second question asked whether preschool-age CWS and CWNS differ in terms of stuttered and non-stuttered disfluencies and whether those two variables possess strong classification capacity, thus being useful for differentiating preschool-age CWS from their CWNS peers. We hypothesized that the entirety of CWS's speech, not merely their stuttered disfluencies, is more disfluent than that of CWNS. Specifically, CWS, when compared to CWNS, were hypothesized to exhibit significantly more stuttered, non-stuttered disfluencies and total disfluencies, and that such speech disfluencies would significantly predict talker group membership. The third question asked whether age, gender, and speech-language ability impact young children's stuttered, non-stuttered, and total disfluencies. We hypothesized that children who have lower speech and language scores will exhibit more disfluencies than those who have higher speech and language scores. The fourth question related to the association of parental expressed concern that their child stutters and examiners’ judgments of stuttering, a particularly salient issue given the common use of “parental concern” to categorize children as stuttering. We hypothesized that there would be a strong association between parents’ expressed concern that their children stutter or are suspected to be stuttering and the frequency of examiner-judged stuttered disfluencies.

Although it was not the purpose of the present study to empirically test extant theories of childhood stuttering, our study did assess four salient issues germane to classification and measurement of childhood stuttering in preschool-age children. Among those issues are non-normality of distributions of speech disfluencies; inclusion of frequency of non-stuttered disfluencies as an additional criterion for talker-group classification to augment the 3% stuttered disfluencies criterion in difficult-to-classify cases, and gender effects on overall fluency of preschool-age children regardless of their talker-group classification. Results of this study provide additional perspective on findings reported by Johnson et al. (1959) as well as others (e.g., Jones et al., 2006). Whereas our findings do not provide an absolute, error-free means for classifying preschoolers who stutter (something seldom possible, if ever, for classification schemas for human disorders), present findings do move us toward a more comprehensive understanding of salient behaviors and characteristics of preschool-age children's stuttering as well as the empirical means to measure same.