Intervention studies with group design targeting expressive phonology for children with developmental speech and language disorder: A systematic review and meta-analysis

Received: 27 January 2023 Accepted: 18 August 2024 DOI: 10.1111/1460-6984.13110 REVIEW Intervention studies with group design targeting expressive phonology for children with developmental speech and language disorder: A systematic review and meta-analysis Sari Kunnari1Susana Sanduvete-Chaves2Salvador Chacon-Moscoso2,3 Dina Caetano Alves4,5Martina Ozbič6Kakia Petinou7 Anna-Kaisa Tolonen1Krisztina Zajdó8Pauline Frizelle9 Carol-Anne Murphy10 David Saldana2Marja Laasonen11 1Research Unit of Logopedics, University of Oulu, Oulu, Finland 2Department of Experimental Psychology, Universidad de Sevilla, Sevilla, Spain 3Departamento de Psicología, Universidad Autónoma de Chile, Temuco, Chile 4School of Health, Polytechnic Institute of Setúbal, Setúbal, Portugal 5Center of Linguistics, School of Arts and Humanities, University of Lisbon, Lisbon, Portugal 6LOGOS, private clinical practice, Sežana, Slovenia 7Department of Rehabilitation Sciences, Cyprus University of Technology Limassol, Limassol, Cyprus 8Department of Special Education/Speech-Language Therapy, Széchenyi István University/The University of Győr, Győr, Hungary 9Department of Speech and Hearing Sciences, University College Cork, Cork, Republic of Ireland 10School of Allied Health, University of Limerick, Limerick, Ireland 11Department of Logopedics, School of Humanities, University of Eastern Finland, Kuopio, Finland Correspondence Sari Kunnari, Research Unit of Logopedics, University of Oulu, Oulu, 90014, Finland. Email: [email protected] Funding information Foundation for Science and Technology; Government of Andalusia; Government of Chile; European Union Abstract Background: Phonological difficulties are prevalent in children with speech and/or language disorders and may hamper their later language outcomes and academic achievements. These children often form a significant proportion of speech and language therapists’ caseloads. There is a shortage of information on evidence-based interventions for improving phonological skills in children and adolescents with speech and language disorder. Aims: The aim of this systematic literature review and meta-analysis was to systematically examine the effects of different intervention approaches on speech production accuracy and phonological representation skills in children with speech and language disorders. Methods: A preregistered systematic review (International Prospective Register of Systematic Reviews ID: CRD42017076075) adhering to Preferred Reporting This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. © 2024 The Author(s). International Journal of Language & Communication Disorders published by John Wiley & Sons Ltd on behalf of Royal College of Speech and Language Therapists. 2686 wileyonlinelibrary.com/journal/jlcd Int J Lang Commun Disord. 2024;59:2686–2705. KUNNARI et al. 2687 Items for Systematic Reviews and Meta-Analyses guidelines was completed. Seven electronic databases (PubMed, Web of Science, ERIC, PsychINFO, Cochrane Library, SCOPUS and Linguistics & Language Behavior Abstracts) were searched for studies related to oral language interventions with children with developmental speech and/or language disorder (mean age ranging from 3– 18 years) published between January 2006 and August 2022. The included articles reported intervention studies with a group design in which speech production accuracy was the outcome measure. Studies were appraised using the Cochrane risk of bias tool, and individual effect sizes were calculated using standardised means differences when enough data was available. A meta-analysis was conducted obtaining the average standardised mean difference d. Heterogeneity, influence of possible moderator variables and publication bias were explored. Results: The 23 studies that met the inclusion criteria presented low-medium risk of bias. Nine effect sizes were obtained from seven of these studies that presented a pre-post-test with a control group design. Medium-high average effect sizes were found in phonological accuracy. Heterogeneity was found between individual effect sizes. Significant moderator variables and publication bias were not detected. Conclusions: The results of this meta-analysis indicate positive effects on speech production accuracy. Based on this review, further improvements in the quality of reporting for intervention research are required in developing the evidence base for practice. KEYWORDS intervention, language disorder, meta-analysis, phonology, speech disorder, systematic review What this paper adds What is already known on the subject ∙An increasing number of interventions is available for children and adolescents with developmental speech and/or language disorders. Previous reviews suggest relatively low levels of evidence of interventions having phonology as an outcome measure. What this paper adds to the existing knowledge ∙This review and meta-analysis summarise the intervention evidence from a substantial body of group design studies, indicating positive results from a range of interventions with phonological outcomes. It highlights the need to systematically implement and replicate different intervention procedures to understand factors that will maximise positive outcomes and to grow the evidence base for best practice. What are the potential or actual clinical implications of this study? ∙Tentative evidence is emerging for the effectiveness of various approaches in enhancing speech production accuracy skills of children and adolescents with developmental speech and/or language disorder. 14606984, 2024, 6, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/1460-6984.13110 by Readcube (Labtiva Inc.), Wiley Online Library on [02/12/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License 2688 GROUP INTERVENTIONS TARGETING EXPRESSIVE PHONOLOGY INTRODUCTION Language acquisition is a complex process extending over a long period. A central component of acquiring an ambient language is to learn the speech sounds of the language and their organization into a system (i.e., phonology). For most children, the acquisition of phonology is relatively easily accomplished before children enter formal schooling, but some may encounter significant difficulties. Developmental language disorder (DLD) is a common neurodevelopmental disorder with no known differentiating condition (e.g., hearing loss, brain injury or genetic syndrome) and with persisting language difficulties (Bishop, 2017;Bishopetal.,2017). It can co-occur with other neurodevelopmental disorders, but their causal connection to language problems is unclear. DLD may cover a broad range of problems affecting speech, language and communication, such as difficulties in the areas of phonology, semantics, morphology, syntax, narrative and discourse skills and/or pragmatics (see Venn diagram in Bishop et al., 2017). Phonology is one area of impairment in DLD, but the diagnostic label excludes children with phonological problems without broader language difficulties or evidence of poor prognosis. Thus, the term Speech Sound Disorder (SSD) has been used for cases that do not warrant a diagnosis of DLD. However, in some cases, judging prognostic indicators may be difficult. Current evidence suggests that more than one-third of young children with DLD or SSD exhibit co-occurring features of both conditions (Rodgers et al., 2023). The terminology describing SSDs has varied and changed over time (Dodd, 2014; Stringer et al., 2023). McLeod and Baker (2017) define SSDs as difficulties with speech production and/or perception consisting of both phonological and motor speech disorders that are not typical of the child’s age, cognitive capacities and language background. Phonological speech disorders reflect a cognitive-linguistic difficulty in learning a consistent phonological system of a language, while motor speech disorders (i.e., articulation disorder, childhood apraxia of speech (CAS) and childhood dysarthria) reflect difficulty with the coordination and production of accurate mouth movements, respiration and/or phonation required for fluent speech. Both disorders may affect speech intelligibility. Stringer et al. (2023), in their recent focused literature review, proposed three levels of diagnostic labels for SSDs. At level 1, SSD is used as an overarching term for all childhood speech disorders. At level 2, SSD is divided into SSD with unknown origin and SSD associated with a medical condition and/or underlying deficit (e.g., hearing loss, cerebral palsy or cleft palate). At level 3, SSD is further divided into a motor difficulty that affects articulation and a linguistic difficulty that affects phonology. The focus of the current review is on phonology (i.e., excluding SSDs associated with medical conditions or underlying deficits or motorically based difficulties). It has been estimated that approximately 7% to 10% of children exhibit language disorder (Norbury et al., 2016; Tomblin et al., 1997), with many more children experiencing delayed speech and language development in the preschool or early school years. In a longitudinal cohort study, McKean et al. (2017) showed that almost 19% of 7- year-old children met the criteria for low language in a large sample investigating speech and language impairments. McLeod and Harrison (2009) found that about 25% of parents had concerns about their child’s speech and language production. Furthermore, the comorbidity of DLD and SSD has been found to be high. Broomfield andDodd(2004) reported that about two-thirds of children with receptive language difficulty and over half of children with expressive language difficulty have co-occurring SSD. Correspondingly, Eadie et al. (2015) found a 40% comorbidity of language disorder and SSD at the age of 4 years. Research has emphasised especially a link between DLD and phonological SSDs due to their shared linguistic deficits (Bishop et al., 2017; Rodgers et al., 2023). Developmental speech and language disorders may persist into adolescence and even adulthood despite intervention and may hamper academic achievements, social-emotional health and employment (e.g., Law et al., 2009; Lewis et al., 2015; Norbury et al., 2016). Intervention approaches Children with phonological problems often form a significant proportion of speech and language therapists’ caseloads (Joffe & Pring, 2008; McLeod & Baker, 2017; Mullen & Schooling, 2010). When determining a suitable approach for each individual, several factors (e.g., child’s age, error type, severity of the condition and underlying cause) need to be taken into account (Cabbage & DeVeney, 2020; Waring & Knight, 2013). As phonological problems vary widely according to underlying aetiology and severity, various approaches reflecting different theoretical accounts have been used for intervention. One way of grouping these approaches is to divide them into perceptually based (i.e., input-oriented), phonologically based and motorically based (i.e., output-oriented) approaches (see e.g., Cabbage & DeVeney, 2020; Rvachew & Brosseau-Lapré, 2018). Children with phonological disorders may have difficulties with phonological processing, 14606984, 2024, 6, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/1460-6984.13110 by Readcube (Labtiva Inc.), Wiley Online Library on [02/12/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License KUNNARI et al. 2689 and a minority of them may as well have auditory processing difficulties (Rvachew & Brosseau-Lapré, 2018,p. 446). These difficulties often manifest as poor speech perception and phonological awareness skills. Therefore, perceptually based approaches (e.g., ear training or focused stimulation procedure) that strengthen acoustic-phonetic representations of words are needed. In the literature, links between children’s speech production difficulties measured with the percentage of consonants correct (PCC), among other variables and underlying phonological representations have been identified (Sutherland & Gillon, 2007). Children may also have limitations in phonological knowledge (Dodd et al., 2008). This in turn suggests underlying deficits in relevant cognitive-linguistic processes. In this case, phonologically based approaches (e.g., contrastive approaches) that aim to reorganise a child’s linguistic system may be beneficial. For inconsistent speech disorder, core vocabulary intervention targeting lexical consistency may be used. When children have concomitant phonology and morphosyntax difficulties, the morphosyntactic approach—targeting, for example, the production of finite morphemes—can also be used alongside other phonological approaches (McLeod & Baker, 2017). Motorically based approaches (e.g., traditional articulation intervention or use of production cues) are also used to supplement perceptually and phonologically based approaches. The aim of motorically based approaches is to improve children’s motor speech control to establish articulatory placements and movements (Cabbage & DeVeney, 2020). Two surveys of clinical practice in the United Kingdom for phonological disorders have indicated that several intervention approaches are used to promote speech and language abilities and to remove barriers to participation in society (Hegarty et al., 2018; Joffe & Pring, 2008). The three approaches used most often by clinicians were auditory discrimination, minimal pair intervention and phonological awareness interventions. Furthermore, Hegarty et al. (2018) identified traditional articulation therapy as one of the most popular approaches to remediating phonological disorders. In addition to the approaches listed above, McLeod and Baker (2014) identified four other frequently used approaches in their survey of Australian speech-language pathologists (i.e., cued articulation, auditory bombardment, Nuffield CentreDyspraxia Programme and core vocabulary). The findings from the surveys mentioned also indicated that eclectic intervention, blending different approaches is quite often adopted in clinical practice instead of a single approach. In any case, accurate diagnosis and labelling of subtypes of DLD and SSD are crucial for the choice of effective approaches (Stringer et al., 2023). Effectiveness of intervention Three previous reviews were identified that examined the effectiveness of intervention approaches for phonological disorders. In Baker and McLeod’s (2011), narrative review of children with SSD, 134 eligible studies with different research designs and participants ranged in age between 1.11 and 10.5, and with or without concomitant difficulties (e.g., hearing loss, cleft lip and/or palate or stuttering) were identified. Studies described seven distinct approaches for target selection and 46 for intervention. Most studies indicated relatively low levels of evidence, and the benefits of different approaches were difficult to interpret, because various research outcomes and designs were employed. Wren et al. (2018) expanded the work of Baker and McLeod (2011) by conducting a systematic review of interventions for preschool children that categorised the included studies (n=26) according to the procedure used in the intervention (i.e., environmental, auditory–perceptual, cognitive–linguistic, production and integrated approaches), and by including speech motor difficulties as well as phonological difficulties. The approaches were organised according to the area targeted in the intervention (i.e., the area where change was expected to occur). Wren et al. found initial evidence for the effectiveness of auditory–perceptual and integrated intervention approaches for children with SSD. A recent scoping review by Rodgers et al. (2022) explored evidence for interventions for preschool children with co-occurring phonological SSD and expressive language difficulties. They found emerging evidence for both integrated (i.e., speech and language) and single-domain (i.e., either speech or language) interventions. In addition to these three systematic reviews focusing specifically on interventions for phonological disorders, Law et al. (2004) conducted a meta-analysis of interventions targeting phonology, syntax or vocabulary for children with primary speech and language disorders. They included data from randomised controlled trials only. Their findings suggested that interventions for phonological disorders were effective. The effect size increased either when parent-implemented interventions or interventions lasting less than 8 weeks were excluded. Furthermore, Law et al. (2012, 2015) conducted a study in which they synthesised the evidence underpinning interventions for children with speech, language and communication needs, using different data sources such as online surveys to practitioners, research literature and parent reports. They identified 58 interventions used in England by speech and language therapists (SLTs) to improve speech and language skills. The level of evidence for the interventions used by SLTs varied considerably, with 5% considered to 14606984, 2024, 6, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/1460-6984.13110 by Readcube (Labtiva Inc.), Wiley Online Library on [02/12/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License 2690 GROUP INTERVENTIONS TARGETING EXPRESSIVE PHONOLOGY have strong evidence, 56% moderate evidence and 39% an indicative level of evidence. Reviews focusing on the effectiveness of a specific type of intervention (e.g., non-speech oral motor treatment; Lee & Gibbon, 2015; McCauley et al., 2009) or intervention outcomes for children with CAS (e.g., Ballard et al., 2015; Morgan et al., 2018; Murray et al., 2014) or multilingual children with speech and language difficulties (Crowe et al., 2021) have also been reported. As the current review excluded studies concerning CAS and multilingualism, these reviews are not discussed in detail. The studies summarised here have provided valuable information and insights into the specific questions they address. The present systematic review and meta-analyses will expand the previous reviews by systematically examining the evidence for different intervention approaches having phonology as an outcome measure with participants across a wide age range (i.e., M=3−18 years). For the meta-analysis, the PCC score was used as an outcome variable and found to be a good indicator of phonological ability (Fabiano-Smith & Hoffman, 2018). Unlike the previous reviews, the present review will focus on group design studies to run meta-analyses when sufficient information is available. Aims To our knowledge, no meta-analysis has previously synthesized the available evidence regarding speech production accuracy in children with developmental speech and/or language disorder. The aim of this study was therefore to identify, appraise and systematically synthesise quantitative evidence from group design interventions to treat children’s developmental speech and/or language difficulties and for which phonology was an outcome measure. The review attempts to extend previous research by addressing the following questions: 1. Which approaches to intervention are used to treat phonological difficulties in preschool and school-age children with developmental speech and/or language difficulties? 2. What is the overall treatment effect of interventions on children’s phonological skills? 3. Are there any associations between potential moderator variables (i.e., percentage of males, mean age in the treatment group, setting, practitioner, model of delivery, theoretical approach, level of service delivery, use of computer-based software and unit of allocation) and the individual effect sizes? METHODS The systematic review was guided by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA; Page et al., 2021) and is one of a series completed as part of European COST Action 1406 (see also Frizelle et al., 2021a, 2021b; Law et al., 2019). It was preregistered with the International Prospective Register of Systematic Reviews (ID CRD42017076075; Kunnari et al., 2017), an international prospective register of systematic reviews. The review is the first of three applying a similar methodology and focusing on interventions for children with developmental speech and/or language disorder, with phonology as an outcome measure. This first review focuses on group studies with speech production outcomes. The focus of the other reviews is on papers in which phonological processing outcomes are reported and on single case study designs. Search procedure A systematic and comprehensive literature search common for several COST Action IS1406 reviews with differing foci (i.e., vocabulary, phonology, morpho-syntax, pragmatics and dosage) was conducted to identify empirical peer-reviewed articles in any language related to speech and/or language interventions with children with DLD. A search strategy is detailed in Supplementary Material S1. Although the search in this initial stage was mainly focused on children with language disorders, we ensured that the search also captured relevant studies with children with SSD when the reviews with differing foci were split into different domains (see selection procedure). The following quality-controlled databases were used: PubMed, Web of Science, ERIC, PsychINFO, SCOPUS, and Linguistics & Language Behavior Abstracts. The search was limited to peer-reviewed studies published between January 2006 and August 2022 (an initial database search covering studies published between January 2006 and December 2015, followed by four updated searches). Inclusion and exclusion criteria The inclusion criteria common for all COST Action IS1406 reviews with different foci were: - Peer-reviewed article published in any language between January 2006 and August 2022. - Participants with a mean age of ≥3and≤18 years and identified as having a DLD or an equivalent term (i.e., 14606984, 2024, 6, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/1460-6984.13110 by Readcube (Labtiva Inc.), Wiley Online Library on [02/12/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License KUNNARI et al. 2691 performance falling below 1 SD in one or more domains using a standardised assessment method). - Examined an oral intervention, which measured outcomes in the domains of vocabulary, phonology, morpho-syntax and/or pragmatics. The exclusion criteria common for all COST Action IS1406 reviews with different foci were: - Participants had autism spectrum disorder, a hearing impairment, an intellectual disability, a brain injury, a physical disability or a learning disability. The inclusion criteria specific to the current review were: - Peer-reviewed article published in English between January 2006 and August 2022 - Any group design study that provided data on expressive phonology outcomes. - Monolingual (i.e., at least 90% of the study participants were required to be monolingual) participants identified as having a DLD or an equivalent term (i.e., performance falling below 1 SD on one or more domains) and/or clinically significant SSD based on articulation/phonology assessment or other standardised articulation/phonology measure. The exclusion criteria specific to the current review were: - Participants with a diagnosis of CAS, childhood dysarthria or articulation disorder (i.e., motorically based disorders) according to judgement by the authors or were bi/multilingual. - Studies with single case design. - Studies that provided data on phonological processing outcomes only. Selection procedure Stage 1. The aim of the initial search common for several COST Action IS1406 reviews was to identify articles examining evidence for different intervention approaches for children with DLD across different language domains. DLD was defined as a significant delay in oral language skills in a child’s first language relative to those of children of the same age. All combinations of terms describing participants’ age, disorder and intervention were searched for in each database (see Appendix A for a detailed search string). These database searches resulted in 17 005 studies (see Figure 1). Stage 2. All citations retrieved from the search process were uploaded to the EPPI-Reviewer 4 software developed for literature reviews. The search results were screened by title and abstract for eligibility criteria based on date, target group, level of evidence or evaluation of an intervention by C.A.M., D.S. and P.F. Twenty percent were initially doublescreened for reliability (C.A.M. and D.S. for the first search and C.A.M. and P.F. for updated searches). There was a 96% agreement rate, and disagreements were reconciled at this stage and all subsequent stages by consensus. This yielded 1358 papers. Stage 3. As the focus of the current review is on phonology outcomes, the studies were next screened for relevance specifically to phonology. In this stage, the included results from the first stage search and screen were checked for the inclusion of key papers linked to theme-relevant (i.e., phonology) terms (phoneme* OR phonolog* OR articulat* OR speech OR phonet). Two independent reviewers (S.K. & M.L.) screened 100% of the papers. The agreement rate was 93%. This stage yielded 796 papers. Full paper copies of these potentially relevant studies were then retrieved for further systematic screening. To identify any additional potentially relevant papers, supplementary hand searches and citation chaining of the reference lists of all the papers included in the full-text stage were undertaken by one author (A.K.). In addition, relevant systematic reviews were also cross-checked. Stage 4. At the full-text stage, studies were screened for eligibility based on their full content by the same independent reviewers as in the previous stage. The agreement rate was 94%. This full-text stage yielded 208 papers for data extraction. Stage 5. Full texts were further screened to include (a) group design, (b) papers with a specific focus on speech production outcomes and (c) articles published in English. Studies with single case designs and phonological processing outcomes were excluded because they were the focus of two forthcoming reviews. In addition, studies where the authors explicitly reported that the participants’ speech difficulties were associated with motorically based disorders (i.e., CAS, childhood dysarthria and articulation disorder) were excluded because these disorders are not considered to have a cognitive-linguistic basis. Furthermore, all non-English articles were excluded because the authors were unable to recruit native speakers of the other languages in question. The agreement rate at this stage was 100%, yielding 23 papers. Data extraction Full-text articles that met the inclusion criteria were read in detail, and data were extracted. The extracted data included the following variables: study design (e.g., randomised controlled trials, quasi-experimental, cohort 14606984, 2024, 6, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/1460-6984.13110 by Readcube (Labtiva Inc.), Wiley Online Library on [02/12/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License 2692 GROUP INTERVENTIONS TARGETING EXPRESSIVE PHONOLOGY FIGURE 1 Preferred Reporting Items for Systematic Reviews and Meta-Analyses flowchart of the process of study selection. Abbreviation: SR, systematic review. analytical, case design), participant details (e.g., number, sex, mean age at intervention baseline), intervention details (e.g., setting, practitioner/s, ingredients, model of delivery, theoretical approach, level of service delivery and software used), and outcome measures (nature of measures, values, main findings). The outcome variables were those described in our pre-registration and present in the data (e.g., speech production accuracy, speech intelligibility, phonemic inventory). The methods used to measure outcomes at the pre- and post-assessment stages 14606984, 2024, 6, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/1460-6984.13110 by Readcube (Labtiva Inc.), Wiley Online Library on [02/12/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License KUNNARI et al. 2693 and intervention effect were the following: two groups (pre- and post-assessment mean, standard deviation, and N for the groups) and one group (pre-post mean and standard deviations or their differences and N for the group). The complete extraction table is available from the authors if required. A total of six coders completed the data extraction independently: two coders (D.C.A. and M.O.) extracted the study design and participant details, two coders (S.K. and K.Z.) the intervention details, and two coders (M.L. and K.P.) the outcome measures. Any disagreement was resolved by consensus. Using the Cochrane risk of bias tool (Higgins et al., 2017), the included studies were assessed for quality by two independent coders (S.K. and K.Z.). The tool assesses risk of bias using the following categories: selection bias for random sequence generation and for allocation concealment, performance bias, detection bias, attrition bias, reporting bias and other possible bias. Each item of bias was rated as low risk (0 points), high risk (2 points) and unclear risk (1 point), with a total risk of bias score ranging from 0 to 14. In addition, an indicator for the fidelity of intervention (i.e., whether the intervention was delivered as intended) was used. Any disagreements between coders were resolved by consensus. Data analysis In preparation for analysis by the type of outcome measure reported, we obtained scores for speech production accuracy (i.e., PCC). This dependent variable was used to examine the effectiveness of an intervention. We used this specific dependent variable because of the availability of the data (it was the variable most commonly reported to measure speech production accuracy in the studies included). The individual effect size was calculated using standardised means differences (d), which indicates the number of standard deviations of difference that there is between the results of the two groups being compared (treatment and control group). The average standardised means differences were then calculated for pre-test—posttest comparison with a control group) and each dependent variable. In all cases, p<0.05 was considered a significant result, and following Cohen’s classification (1988), 0 was considered a null effect size, around ±0.2 low, around ± 0.50 medium and around ±0.80 high. To measure heterogeneity, we considered three calculations: a Qstatistic with p<0.05 was interpreted as the individual effect sizes differed statistically between studies; I2was interpreted as the percentage of explained variability that could be attributed to study differences (around 25% would be deemed a low percentage variability, around 50% medium and around 75%, high); and the predictive interval was interpreted as the lowest and the highest possible effect size obtained in the population. When there was heterogeneity, meta-regression was used to study the possible relationship between the quantitative moderator variables and the individual effect size; where the moderator variable was qualitative (such as the setting of intervention – preschool, school, or clinic – or the model of delivery – direct or indirect), a comparison across groups was carried out. Finally, to show publication bias, funnel plots were created. White symbols were the observed values, while black symbols were those that were imputed. When the white diamond was close to the black diamond, we concluded that there was no meaningful publication bias (Borenstein, 2019; Borenstein et al., 2009). RESULTS Study characteristics Of a database of 17 005 papers, 23 studies met the inclusion criteria for this review. Table 1provides a summary of the included studies’ descriptive characteristics. Fortythree percent of these 23 studies originated from the United States or Canada. Other contributing studies were from the United Kingdom, Australia, Portugal, Brazil, Finland, Germany and Turkey. A total of 925 children were represented in these 23 studies. The sample sizes varied from 14 to 126 children, and the range of the children’s mean ages was from 3 to 17 years. In the two articles where specific mean ages were not presented, the age was presented in ranges: between 5 and 15 years old, and from preschool to 15 years old. In all the studies (in which the information was stated), there were more boys (n=582, 66.5%) than girls (n=293, 33.5%) in the samples. The participants in the studies were characterised to have DLD only (n=4, 17.4%), both speech and language disorder (n=5, 21.7%), either speech and/or language disorder (n=7, 30.4%), or SSD only (n=7, 30.4%). Fifty-two percent of the studies were randomised controlled trials (n=12), 17% were quasiexperimental (n=4) and 30% were cohort studies (n=7) in design. Intervention characteristics and outcomes Interventions were intended to develop several phonological skills relevant to this review (e.g., speech accuracy, speech intelligibility, speech stimulability; see Table 1). Interventions were delivered either in educational (n =12, 52.2%) or clinical (n=9, 39.1%) settings. In two 14606984, 2024, 6, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/1460-6984.13110 by Readcube (Labtiva Inc.), Wiley Online Library on [02/12/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License 2694 GROUP INTERVENTIONS TARGETING EXPRESSIVE PHONOLOGY TABLE 1 Description of included studies. Study Study design Participants (N,age) Setting Agent of delivery Intervention approaches Phonological outcome measures Main findings Allen (2013)RCT 543.0−5.5 E SLT Two groups receiving multiple opposition approach with different dose frequency and a control group receiving storybook intervention PCC Multiple opposition group with a more intensive dose frequency had significantly better outcomes than two other groups. Catt et al. (2011)Cohort study 20 Preschool−15 years CSLT student Thematic language intervention Articulation score Articulation scores improved significantly. Dodd et al. (2008) RCT 19 3.11−6.05 C SLT Minimal vs. non-minimal contrasts PCC, PVC, PPC, number of error patterns Positive outcomes in terms of speech accuracy and number of error patterns but no group differences. Ebbels et al. (2017) Cohort study 72 9.2−17.0 ESLT Individual speech and language intervention Speech sound production The targeted areas improved significantly. Farquharson et al. (2020) Cohort study 126 5−8 years E SLT Business-as-usual therapy PCC Children made significant gains in PCC. Fey et al. (2010)RCT 23 6−8 years C SLTs and SLT students a. Fast ForWord-Language and Narrative-Based Language Intervention group b. NBLI/FFW-L group, and c. wait/NBLI group PPC The intervention groups significantly outperformed the no-treatment wait/NBLI group. Gabel et al. (2013) Cohort study 71 5−15 years E SLT Telepractice speech-language intervention Speech sound production, speech intelligibility 85% made progress in speech sound production, and 67% in speech intelligibility. Gierut et al. (2010) Retrospective cohort study 60 3.1−7.5 CSLT Treating sounds in error with nonword vs. real word stimuli Speech accuracy Generalization accuracy of the treated sounds exceeded that of untreated sounds, and nonwords induced greater and more rapid generalization than real words. (Continues) 14606984, 2024, 6, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/1460-6984.13110 by Readcube (Labtiva Inc.), Wiley Online Library on [02/12/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License KUNNARI et al. 2701 geting phonology are effective (e.g., Baker & McLeod, 2011; Law et al., 2004;Wrenetal.,2018). Although individual effect sizes were heterogeneous, no significant moderator variables were found. There was no relationship between effect size and participant (i.e., age of the participants, gender) or intervention characteristics (i.e., setting, practitioners involved, model of delivery, theoretical approach, level of service delivery and use of software). This may, in part, be due to an uneven number of effect sizes across comparison groups and inconsistent reporting of the pertinent participant and intervention characteristics. In a previous meta-analysis (Law et al., 2004) on expressive phonology outcomes, findings showed that effect sizes increased when parent-implemented interventions and interventions lasting less than 8 weeks were removed. In the current meta-analyses, no parent-implemented interventions were included. Nor were dosage effects examined, because they were the focus of two independent reviews of COST Action IS1406. In summary, our review suggests that interventions tend to obtain improvements in children with phonological difficulties. However, the use of numerous techniques and procedures, insufficient data and a lack of study replication make it difficult to determine if any single intervention approach is more effective than another or more suited to specific groups of children with phonological difficulties. Strengths and limitations of the review The strengths of the current systematic review and metaanalysis are the wide age range of participants and the inclusion of group design studies alone. Although most of the included studies focused on pre-schoolers and children in middle childhood, school-age children and adolescents were also involved. While we know that phonological difficulties appear to be resolved for most children by the age of 8−9 years (Shriberg, 2010;Wrenetal.,2012), they may sometimes persist into adolescence or even adulthood affecting 1%−2% of young adults (Flipsen, 2015). This places them at risk of poor academic achievement (Eadie et al., 2015; Lewis et al., 2015). Because the current review concentrated on group design studies, we were able to combine the numerical results of studies, and thus use a meta-analytic approach. Meta-analysis allowed us to statistically combine the results of studies and produce a more precise estimate of the effect of interventions. However, systematic reviews on single-case designs are also needed to provide a rich and in-depth understanding of intervention effects. While the results of the current systematic review and meta-analysis clearly indicate that the overall effects of interventions targeting phonology outcomes were positive, there are several limitations to this review and metaanalysis. Although the ‘grey’ literature (e.g., dissertations and conference papers) may make various positive contributions to systematic reviews, we decided to restrict the scope of this review to published peer-reviewed literature. We took this decision because the grey literature may add a publication bias to the findings (Adams et al., 2017), and because we wanted to include the studies that were most likely to be of high quality by virtue of being published, thus enabling us to answer our research questions robustly. Because the current review was part of a larger piece of work (i.e., COST Action IS1406 focusing on interventions for children with difficulties learning their first language), the search terms common for all COST Action reviews with different foci were used. Thus, no SSD-related search terms were included. However, the authors ensured that the literature search also captured SSD-related studies by using hand searches and citation chaining to identify any potentially relevant studies. In addition, while the authors aimed to include literature published in languages other than English, there was no capacity in this review process to extract data from papers in languages other than English. Finally, some methodological limitations should be considered when interpreting the results of this meta-analysis. Five out of six studies had sample sizes of fewer than 25 participants. In addition to the small sample sizes, our meta-analysis included a total of only seven studies that reported nine effect sizes. The small number of studies led to a lack of variability in data and difficulty in detecting potential significant moderator variables. These limitations restrict the findings’ generalisability. Implications for practice The present study highlights the need to systematically implement and replicate different intervention procedures to understand factors that will maximise positive outcomes and to grow the evidence base for best practice. Since the individual characteristics of the children (e.g., age, motivation, type, and severity of phonological disorder) may predict the response to an intervention, it is also important to study these characteristics to facilitate clinical decision making about which children are most suitable for certain kinds of intervention. In addition, more high-quality comparative studies are needed to verify the effectiveness of different intervention approaches targeting phonology and to guide clinical decision making. In the future, a thor- 14606984, 2024, 6, Downloaded from https://onlinelibrary.wiley.com/doi/10.1111/1460-6984.13110 by Readcube (Labtiva Inc.), Wiley Online Library on [02/12/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License 2702 GROUP INTERVENTIONS TARGETING EXPRESSIVE PHONOLOGY ough investigation of the ingredients of interventions will be needed to identify the active ingredients that are likely to lead to good outcomes. The data-extraction process revealed that many studies reported incomplete data regarding participant characteristics, ingredients of intervention and fidelity measures used in the interventions, for example. This calls for common reporting guidelines for intervention research to enable data pooling and meta-analysis to examine the potential effects of moderating variables on intervention effectiveness, and to enable practitioners to consider the applicability of findings to clinical caseloads (see Frizelle et al., 2022). CONCLUSIONS Overall, the review and our meta-analysis summarise the intervention evidence from a substantial body of literature and indicate positive outcomes from a range of interventions with phonological outcomes in children and adolescents with speech and language difficulties. However, none of the potential moderator variables studied yielded a statistically significant influence on the effect size. Although no publication bias was detected, the conclusions must be considered in the context of the limitations of this meta-analysis and the limitations of the individual studies. ACKNOWLEDGEMENTS The systematic review was part of the work of the Cost Action IS1406 network entitled Enhancing Children’s Oral Language Skills Across Europe and Beyond—A Collaboration Focusing on Interventions for Children with Difficulties Learning Their First Language. The network was supported by COST (European Cooperation in Science and Technology), funded by the European Union (Grant COST 106/14). This work was also supported in part by the Chilean national projects FONDECYT Regular 2019, Government of Chile, Chile [1190945], the Operational Program ERDF Andalusia 2014–2020, Government of Andalusia, Spain [US-1263096], the grant PID2020-115486GB- I00 funded by MCIN/AEI/ 10.13039/501100011033, and by the Fundação para a Ciência e a Tecnologia (FCT, Foundation for Science and Technology), grant UIDB/ 00214/2020. CONFLICT OF INTEREST STATEMENT The authors have no conflicts of interest to declare. DATA AVAILABILITY STATEMENT Data are available as Supplementary Material. 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