A Diagnostic Marker to Discriminate Childhood Apraxia of Speech From Speech Delay: IV. The Pause Marker Index

Abstract

Purpose: Three previous articles provided rationale, methods, and several forms of validity support for a diagnostic marker of childhood apraxia of speech (CAS), termed the pause marker (PM). Goals of the present article were to assess the validity and stability of the PM Index (PMI) to scale CAS severity. Method: PM scores and speech, prosody, and voice precision-stability data were obtained for participants with CAS in idiopathic, neurogenetic, and complex neurodevelopmental disorders; adult-onset apraxia of speech consequent to stroke and primary progressive apraxia; and idiopathic speech delay. Three studies were completed including criterion and concurrent validity studies of the PMI and a temporal stability study of the PMI using retrospective case studies. Results: PM scores were significantly correlated with other signs of CAS precision and stability. The best fit of the distribution of PM scores to index CAS severity was obtained by dividing scores into 4 ordinal severity classifications: mild, mild-moderate, moderate-severe, and severe. Severity findings for the 4 classifications and retrospective longitudinal findings from 8 participants with CAS supported the validity and stability of the PMI. Conclusion: Findings support research and clinical use of the PMI to scale the severity of CAS.A four-article series (Shriberg et al., 2017a(Shriberg et al., , 2017b(Shriberg et al., , 2017c, and the present article) to develop and assess the theoretical and clinical utility of a singlesign, behavioral marker of childhood apraxia of speech (CAS) poses the following three questions: 1.Do findings from construct and criterion validity studies support the diagnostic accuracy of a behavioral marker, the pause marker (PM), to discriminate CAS from speech delay (SD)?2. Do findings from the PM and other measures support the hypothesis of core representational and transcoding deficits in CAS, and is the PM theoretically coherent with those deficits?3. Do findings from cross-sectional and retrospective longitudinal case studies support an ordinal scale of PM scores, the Pause Marker Index (PMI), to quantify the severity of CAS for research and clinical applications?The short-term goal of the PM is to provide a behavioral marker of CAS for research and clinical practice. A longer term goal of the PM is to provide quantitative inclusionary and exclusionary criteria to identify participants who are true positive for CAS in studies to identify and validate a biomarker of CAS. The present article addresses both goals. As proposed in the first article in this series (PM I; Shriberg et al., 2017a, Table 1), a highly valued attribute of diagnostic markers is generality, that is, a marker has research and clinical utility beyond identifying presence or absence of a disorder. In the present context, a behavioral marker of CAS has research and clinical generality when in addition to being diagnostically sensitive to and specific for a prior, active, and/or future disorder, it also quantifies the severity of the disorder. The three...

A Diagnostic Marker to Discriminate Childhood Apraxia of Speech From Speech Delay: I. Development and Description of the Pause Marker

“…We define a diagnostic marker of a disorder as "one or more operationalized and standardized signs with sensitivity to and specificity for persons with prior, present, and/or future expression of the disorder at estimated levels of accuracy." Some diagnostic markers may have only categorical properties (i.e., presence/absence of disorder), whereas markers that meet distributional criteria for ordinal or interval measurement levels may also be used to scale the severity of a disorder (see PM IV; Shriberg et al, 2017c). As defined herein, positive status for a conclusive behavioral diagnostic marker is the ideal inclusionary criterion on which researchers can base the identification and development of biomarkers for diseases or disorders.…”

“…A marker with such properties to use as the inclusionary criterion in CAS research requires psychometric support for its diagnostic accuracy and empirical support for its theoretical coherence with the speech processing deficits proposed to define CAS. The research reported in the present article (PM I), in PM II (Shriberg et al, 2017a), and in PM IV (Shriberg et al, 2017c) addresses the former needs, with findings in PM III (Shriberg et al, 2017b) assessing the latter need for theoretical coherence. The following review includes relevant terms and concepts in classification, speech processes, and diagnostic marker research in CAS.…”

A Diagnostic Marker to Discriminate Childhood Apraxia of Speech From Speech Delay: II. Validity Studies of the Pause Marker

“…PM IV (Shriberg et al, 2017c): Question 3. Do findings from cross-sectional and retrospective longitudinal case studies support an ordinal scale of PM scores, termed the Pause Marker Index, to quantify the severity of CAS for research and clinical applications?…”

A Diagnostic Marker to Discriminate Childhood Apraxia of Speech From Speech Delay: III. Theoretical Coherence of the Pause Marker with Speech Processing Deficits in Childhood Apraxia of Speech

“…The availability of the several etiologically and demographically diverse databases assembled in the development of the PM and the PMI (see PM IV; Shriberg et al, 2017c) provided the opportunity to address the second of the three questions posed in this series:…”

“…T he second article in this series (PM II;Shriberg et al, 2017b) described rationale and validity support for a diagnostic marker of childhood apraxia of speech (CAS) termed the pause marker (PM), and a following article (PM IV; Shriberg et al, 2017c) reports validity support for an ordinal severity scale for the PM termed the pause marker index (PMI). The present article assesses the theoretical coherence of the PM with speech processing deficits in CAS.…”