Estimates of the prevalence of motor speech disorders in children with idiopathic speech delay

Figures & data

Figure 1. The Speech Disorders Classification System (SDCS).

Table 1. Assessment, demographic, cognitive-language, and speech information for participants in six groups of children in six USA cities recruited for idiopathic SD. The groups are listed in descending order by the number of participants in each original sample. Cell values and percentages for demographic, cognitive-language, and speech variables are for the 415 of the original 448 (93.5%) participants that were able to be classified using the SDCSS.

	Assessment			Demographic				Cognitive-Language				Speech
	Original Group	SDCSS Classified		Age (yrs)		Sex (%)		Cognition^a		Language^b		PCC^c		II^d
Group	n	n	%	M	SD	% Female	% Male	M	SD	M	SD	M	SD	M	SD
Idiopathic SD
Group 1	200	188	94.0	4.4	1.1	33.5	66.5	109.4	13.3	99.1	10.5	69.5	12.0	91.3	8.1
Group 2	84	72	85.7	4.0	0.7	26.4	73.6	*	*	*	*	70.0	9.6	88.5	8.9
Group 3	71	67	94.4	5.1	1.5	22.4	77.6	96.3	12.8	95.3	14.5	80.6	11.2	94.4	7.2
Group 4	26	26	100.0	7.8	1.1	30.8	69.2	104.7	12.6	95.0	20.2	89.8	7.1	97.3	2.7
Group 5	22	21	95.5	5.5	0.6	23.8	76.2	*	*	*	*	82.8	6.1	91.7	12.2
Group 6	45	41	91.1	6.2	2.6	19.5	80.5	*	*	*	*	77.5	11.4	86.8	11.0
Total	448	415	93.5	5.5	1.3	26.1	73.9	103.5	12.9	96.5	15.1	78.4	9.6	91.7	8.4

Notes: SD = Speech Delay; SDCSS = Speech Disorders Classification System Summary; PCC = Percentage of Consonants Correct; II = Intelligibility Index, * = no data.

^a Standard scores for IQ Composite: Kaufman Brief Intelligence Test – Second Edition; Kaufman and Kaufman (2004). IQ Scores: Stanford-Binet-4^th Edition; Thorndike, Hagen, and Sattler (1986).

^b Standard scores for Oral Composite: Oral and Written Language Scales (OWLS); Carrow-Woolfolk (1995). Standard scores for Core Language: Clinical Evaluation of Language Fundamentals-4 (CELF–4); Semel, Wiig, and Secord (2003).

^c Shriberg et al. (1997).

^d Shriberg (1993).

Table 2. The five speech classifications and five motor speech classifications in the SDCS are each mutually exclusive. The five dysarthria subtype classifications are not mutually exclusive. That is, a speaker can meet percentile criteria for more than one of the five listed dysarthria subtype classifications (i.e., mixed dysarthria). See Supplement for the procedures and measures used to classify each motor speech disorder.

SDCS Classifications and Dysarthria Subtypes	Abbreviation	Age (yrs;mos) at Assessment	Description	References^a
Five Speech Classifications
Normal(ized) Speech Acquisition	NSA	3–80	Does not meet criteria for any of the four Speech Disorder classifications	2, 3, 4
Speech Errors	SE	6–8;11	Age-inappropriate speech sound distortions	3, 4
Persistent Speech Errors	PSE	9–80	Age-inappropriate speech sound distortions that persist past 9 years of age	4, 5
Speech Delay	SD	3–8;11	Age-inappropriate speech sound deletions and/or substitutions	3, 4
Persistent Speech Delay	PSD	9–80	Age-inappropriate speech sound deletions and/or substitutions that persist past 9 years of age	3, 4, 5
Five Motor Speech Classifications
No Motor Speech Disorder	No MSD	3–80	Does not meet criteria for any of the four Motor Speech Disorders classifications	2, 6, 8
Speech Motor Delay	SMD	3–80	Meets PSI criterion for SMD	2, 6, 8
Childhood Dysarthria	CD	3–80	Meets DI and DSI criteria for CD	2, 6, 8
Childhood Apraxia of Speech	CAS	3–80	Meets PM criterion for CAS	6, 7, 8
Childhood Dysarthria & Childhood Apraxia of Speech	CD & CAS	3–80	Meets SDCS criteria for CD & CAS	2, 6, 8
Five Dysarthria Subtypes
Ataxic		3–80	Cerebellar disorder	1, 2
Spastic		3–80	Upper motor neuron disorder	1, 2
Hyperkinetic		3–80	Basal ganglia disorder; increased movement	1, 2
Hypokinetic		3–80	Basal ganglia disorder; decreased movement	1, 2
Flaccid		3–80	Lower motor neuron disorder	1, 2

Notes: SDCS = Speech Disorders Classification System; PSI = Precision-Stability Index; DI = Dysarthria Index; DSI = Dysarthria Subtype Index; PM = Pause Marker.

^a 1. Duffy (2013); 2. Mabie and Shriberg (2017); 3. Shriberg (1993); 4. Shriberg et al. (1997); 5. Shriberg et al. (2010a); 6. Shriberg and Mabie (2017); 7. Shriberg et al. (2017a); 8. Tilkens et al. (2017).

Figure 2. Sample output from the Speech Disorders Classification System Summary (SDCSS). The upper SDCSS includes cross-classification findings for a family member with a disruption in FOXP2 (Shriberg et al., 2006). The lower SDCSS includes speech and motor speech cross-classification findings for 45 speakers with Down syndrome (Wilson et al., 2019).

Table 3. Reliability estimates for interjudge and intrajudge agreement for phonetic transcription, prosody-voice coding, and acoustic analyses.

	Agreement Types
Data	Interjudge	Intrajudge	No. of Tokens Analyzed	Variable	Percentage of Agreement
Phonetic Transcription	X			Consonants
			5562 utterances; 12,813 words	Broad	89.5
				Narrow	76.2
				Vowels
				Broad	85.9
				Narrow	74.9
		X		Consonants
			5562 utterances; 12,907 words	Broad	94.5
				Narrow	85.7
				Vowels
				Broad	89.9
				Narrow	81.9
Prosody-Voice Coding	X		1413 utterances	Appropriate-Inappropriate	90.7
		X		Appropriate-Inappropriate	93.9
Acoustic Analyses	X			Phoneme Duration
			1093 Consonants	Consonants	82.6
			4497 Vowels	Vowels	85.6
		X		Phoneme Duration
			1095 Consonants	Consonants	88.9
			4484 Vowels	Vowels	88.8
	X			Vowel Frequency
			4213 Vowels	F0	97.3
			770 Vowels	F1	89.3
			744 Vowels	F2	92.4
		X		Vowel Frequency
			4225 Vowels	F0	97.1
			1011 Vowels	F1	91.3
			977 Vowels	F2	94.7
	X			Pause Variables
			689 Pauses	Pause–Non-Pause	81.1
			559 Pauses	Appropriate–Not Appropriate	84.9
			19 Pauses	Type 1 –Type 2	89.5
		X		Pause Variables
			684 Pauses	Pause–Non-Pause	80.7
			556 Pauses	Appropriate–Not Appropriate	85.4
			13 Pauses	Type 1–Type 2	92.3

Figure 3. Speech and motor speech classification prevalence estimates from six samples of children (n = 415) recruited for idiopathic speech delay.

Table 4. Summary of dysarthria subtype findings for the 14 participants who met Speech Disorders Classification System criteria for childhood dysarthria.

Dysarthria Subtypes^a
Participants	Ataxic	Spastic	Hyperkinetic	Hypokinetic	Flaccid	No. of Subtypes ≤10^th %ile
1	35	30	21	10	20	1
2	35	15	26	6	43	1
3	45	30	21	4	5	2
4	26	4	3	49	35	2
5	2	30	8	18	60	2
6	56	51	69	7	2	2
7	35	72	37	18	2	1
8	10	17	21	30	20	1
9	26	25	30	30	10	1
10	45	60	13	7	1	2
11	45	72	46	7	5	2
12	45	30	37	4	5	2
13	45	51	46	2	2	2
14	56	17	13	4	20	1
n ≤ 10^th %ile	2	1	2	9	8
Percentage ≤10^th %ile	14.3	7.1	14.3	64.3	57.1

^aDysarthria Subtype Indices Percentile Scores ≤10^th percentile are bolded.

Table 5. Estimates of the prevalence of idiopathic MSD. Estimates of the prevalence of MSD in idiopathic SD are from the present study. Estimates of the prevalence of idiopathic SD are from studies in Australia, England, and the USA.

Present Study			Prevalence of idiopathic SD from three population-based samples of children in three countries				Estimates of the population prevalence of idiopathic MSD
SDCS MSD Classifications	Abbreviation	Prevalence Estimate in Idiopathic SD		Eadie et al. (2015)	Shriberg et al. (1999)	Wren et al. (2016)
			Age:	4 yrs	6 yrs	8 yrs	4-8 yrs
No Motor Speech Disorder	No MSD	82.2%	n:	1,494	1,328	7, 390	10,212
Speech Motor Delay	SMD	12.0%	Population-based estimates of
Childhood Dysarthria	CD	3.4%	the prevalence of idiopathic SD:	3.4%	3.8%	3.6%	3.4 - 3.8/100
Childhood Apraxia of Speech Childhood Dysarthria & Childhood Apraxia of Speech	CAS CD & CAS	2.4% 0.0%	SMD CD CAS CD & CAS	0.4% 0.1% 0.1% 0.0%	0.5% 0.1% 0.1% 0.0%	0.4% 0.1% 0.1% 0.0%	4/1000 1/1000 1/1000 0/1000

Note: MSD = Motor Speech Disorder; SD = Speech Delay; SDCSS = Speech Disorders Classification System Summary.

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