Active Ingredients in Quantitative Dosage for Children With Phonological Impairment: A Scoping Review

Speech Sound Disorder (SSD) reduces speech intelligibility, affecting a child's ability to make themselves understood. If SSD is not resolved in the early years it will negatively impact children's education and general well-being. Effective and efficient speech and language therapy is known to resolve SSD and mitigate these risks. Intervention for SSD is often provided in inadequate dosages to be effective or efficient. Quantitative dosage is an overarching term for the different aspects of intensity of intervention which may impact outcomes. Existing literature on quantitative dosage indicates that more intensive therapy approaches for SSD appear to be more effective and efficient than less intensive delivery. A scoping review of current research in this area will serve to clarify evidence-based knowledge and understanding about quantitative dosage, how it works, and how different components potentially interact to contribute to outcomes for children with phonological impairment (PI) (a sub-type of SSD), informing future service developments and research.

This scoping review investigates quantitative dosage elements in interventions for 3-8-year-olds with PI within speech and language therapy-led contexts to identify preliminary evidence and inform reflections for practice and future research. It is registered on the Open Science Framework (OSF) registry (https://osf.io/b3as4/).

The review followed the Population, Concept, Context framework (Joanna Briggs Institute) and is reported in line with PRISMA guidance for Scoping Reviews. Key information sources were searched, including MEDLINE, CINAHL, PsycInfo, EMBASE. Grey literature searching included the COSMIN, PROSPERO, FigShare and Open Science Framework, Google scholar (advanced search), and SpeechBite. Data extraction included intervention approach, quantitative dosage of intervention delivery, outcome measurement tools, and context. The PAGER framework was used for analysis and synthesis of the identified patterns.

Seventy-six papers were extracted for the synthesis. Only four studies specifically investigated the impact of quantitative dosage on outcomes. Three patterns developed across the 76 papers: quantitative dosage is an active ingredient; issues reporting quantitative dosage; characteristics of the evidence base and are discussed in relation to advances in the field, gaps, evidence for practice and research recommendations. Preliminary evidence for practice highlights that aspects of quantitative dosage make an important contribution to effective and efficient intervention for children with SSD. However, rigour and consistency in reporting quantitative dosage should be improved to support translation of evidence to practice and replication of research. The importance of using benchmarked study designs and appropriate methodologies to support robust research to better-inform evidence-based practice is highlighted.

This scoping review provides preliminary evidence for quantitative dosage in children with PI. The findings are promising, (with evidence of some stronger research designs for example, randomised controlled trials, multiple baseline SCEDs with multiple participants, and replication of findings). However, further robust research, reporting all aspects of quantitative dosage and considering the potential costs and benefits of more efficient, evidence-based quantitative dosages is urgently needed.

What is already known on this subject General findings about quantitative dosage for children with SSD show that reporting on dosage is often absent. When dosage is reported it is often under specified or different aspects of dosage are conflated. Reporting standards for dosage need to be agreed. Further research is required about the specific levels of quantitative dosage optimally required before children with SSD are discharged. Previous reviews have mainly extracted evidence about session numbers, session frequency, session length, and dose of practise items per session, across subtypes of SSD. What this study adds to the existing knowledge This paper specifically considers how all aspects of quantitative dosage are reported on and explored in the literature with a focus on children with phonological impairment (PI).  A novel approach following the PAGER framework synthesized the data extracted from the papers to identify Patterns and relate these to clinical practice and research.  The key patterns that emerged in this scoping review were: quantitative dosage is an active ingredient; issues reporting quantitative dosage; and characteristics of the evidence base. Advances, Gaps, Evidence for practice and Research Recommendations (the AGER of PAGER) are reported for each Pattern.  What are the clinical implications of this study? For children with PI, intervention delivered two to four times weekly is likely to be more cost- and clinically effective than once weekly. More sessions delivered over time with a higher dose of production trials per session are likely to be more effective and efficient than fewer sessions delivered with a lower dose (although an upper threshold may exist). Potentially, more timely intervention is more effective over the longer term, than less timely intervention. Further high-quality research is needed because study design, reporting of quantitative dosage, and exploring the cost benefits of more efficient dosages are weaknesses in current literature.