Intervention dose frequency
The study assessed whether the frequency of intervention sessions received (dose frequency) affected the outcomes of an intervention, aiming to improve spoken vocabulary. Participants were 35 children with Down syndrome aged between 18-27 months and a control group of children who did not have Down syndrome, but had intellectual disabilities (n = 28). Approximately half of the children from each population were allocated to a high frequency dose group, while the other half were allocated to a low frequency dose group. Each intervention session was 60 minutes long; the high frequency dose group received five hours of intervention sessions per week, while the low frequency dose group received a one hour intervention session per week. This was over a 9 month treatment.
Yoder et al (2014) direct the reader to the article by Fey et al (2013) for explanation of the intervention. The intervention used milieu communication teaching (MCT). However, Fey et al report only the essential details of the MCT training, directing the reader to Fey et al (2006) and Warren et al (2006) for descriptions of MCT, thus to get a full picture of the intervention when reading the article by Yoder et al it is necessary to refer back to various other articles. The three main intervention components in MCT are; Responsivity education, Prelinguistic Milieu Teaching, and Milieu Teaching. The essential details provided by Fey et al (2013) regarding each MCT component are summarized below:
Responsivity education (RE) sessions; these were weekly and aimed to (a) increase caregivers’ responsiveness to the child’s play actions and attempts to communicate such as imitating the child’s acts and vocalizations or commenting on them, (b) putting the child’s nonverbal communication into words, (c) add more meaning to the child’s topic, the example they give is: child says, “ball,” and the parent responds, “You can bounce it”; or (d) repeat what the child said but with added structure and meaning, such as when the child says ‘A ball’ the parent then says ‘Yeah, it is a ball’.
Prelinguistic milieu teaching (PMT): The aim of PMT is to ‘increase the frequency, clarity and complexity of the child’s nonverbal communication acts’ (pg. 683, Fey et al., 2013), to give the child a solid foundation of nonverbal communication skills to build upon during linguistic development. In PMT the clinician seeks to produce one ‘teaching episode’ each minute. It was hard to fully grasp the key content described by Fey et al (2013); it appears that there are various goals set for each child, such as gestures, and the task is to create opportunities for children to use these communication acts. The sessions do not appear to be systematic, based on the descriptions given by Fey et al (2013).
Milieu teaching (MT): MT is received after PMT. The aim of MT sessions is to increase frequency and/or complexity of verbal communication acts, again aiming for one ‘teaching episode’ each minute. Depending on the child’s current level of vocabulary they had either 5-10 ‘lexical targets’ i.e., words focused on, during the MT sessions, or for children with more advanced vocabularies the goal was to work on ‘multiword semantic relations’; again these essential details of the procedure were not completely transparent from the descriptions by Fey et al (2013). For those readers seeking more thorough details of the procedure we suggest looking back to Fey et al (2006) and/or Warren et al (2006), however, in this blog post we would rather like to focus on the frequency dose.
In addition to MCT most of the participants were receiving treatment by a speech and language therapist.
Results reported by Fey et al (2013) in the original article:
The results of this intervention were first reported by Fey et al (2013); they used growth curve modelling (i.e., to plot the average growth in spoken vocabulary performance across the children over time). They found that children improved significantly over time during the intervention. However, quite surprisingly, children’s growth was not associated with dose frequency. Thus, those receiving more sessions did not have greater outcomes (larger increases in performance over time). Dose frequency had no differential effect on spoken vocabulary as a function of presence or absence of Down syndrome (DS) either. The authors did however find that children who engaged in more functional play with objects (measured via the Developmental Play Assessment, Lifter, 2000) did experience greater gains in vocabulary as a result of high dose frequency compared to low dose frequency MCT. The moderating effect of functional play levels could reflect the child’s engagement in the study sessions, i.e., if they are more engaged then the higher frequency of MCT sessions is effective.
Reanalysis of results, by Yoder et al (2014)
In the article by Yoder et al they re-analysed this same data from the intervention, with the aim to evaluate whether a different (more complex) type of analysis may yield different results. In this re-analysis they again created a growth curve for vocabulary development, however this time in a way that accounts for periods of deceleration (slower growth) and acceleration in growth (faster growth) over time, rather than assuming stable (linear) increases in vocabulary growth over time (for more details of this approach see ‘Statistical Analysis Plan’ in Yoder et al., 2014). They also analyzed those with Down syndrome separately to those without Down syndrome, rather than pooled across both groups. When reanalyzing the data in this way, they detected some additional findings that were not detected in the original analysis by Fey et al (2013). Specifically, they found for those with Down syndrome, receiving a higher frequency dose was beneficial (relative to the low frequency dose), resulting in them producing more words post-treatment. However, for the group without Down syndrome this was not the case. The effect of object play did remain across both groups, with those children who engage in more functional play showing greater gains as a result of a higher dose relative to the lower frequency dose intervention.
Session frequency and session content
The authors conclude that increasing intensity of milieu communication teaching (MCT) by dosage (more sessions) does not necessarily result in improvements in the effect of that treatment for all children. These findings suggest rather, that the extra sessions of MCT have to be planned in such a way that the child is engaged in the sessions. We can take this into consideration when thinking about how each session during any intervention is helping the child to learn, build upon and consolidate knowledge. Various factors could interact with dose frequency. The content of the sessions in a high dose condition could involve different levels of variability, content shown in a different context or format, repetitions of previous sessions for consolidation, or coverage of new additional content. Levels of interaction in the sessions is also important to consider, for instance with respect to how motivated and engaged the child is during the sessions.
The finding that specific groups were affected differently based on the Yoder et al (2014) analyses highlights the relevance of designing interventions for specific populations based on their specific group profiles, while allowing for flexibility to meet individual differences in needs and preferences. The finding of dose frequency effects in those with Down syndrome but not in the control group, may reflect an importance of repetition for children with Down syndrome. Though, it may also be important to consider the relatively small sample size in these split analyses and the effect this may have on results. It would of course be useful to assess dose frequency with other types of interventions, where measures are taken to further promote task engagement in all sessions, and more children are included in the sample.
The study has a particular focus on individual factors and the Down syndrome etiology, aspects such as children’s language profile and their potential tendency for task resistance are especially mentioned as potential factors that may explain variability in response to intervention.
We would suggest that factors non-specific to the Down syndrome etiology, such as children’s socioeconomic status (SES) may also be an important variable with respect to their treatment outcomes and this could interact with effects of intensity such as dose frequency. SES has often been shown to relate to children’s learning outcomes, particularly with regards to language ability (Hart & Risley, 1995, Hoff, 2003; 2013; Hoff-Ginsberg, 1998)
To summarize, increased dose frequency does not improve MCT treatment outcomes for all children. However, engagement appears to be an important moderating factor, indicating that when children are potentially more engaged in sessions, the outcomes may be more successful. For those with Down syndrome, higher dose frequency of MCT was beneficial. The article by Yoder et al highlights that how growth is modelled (e.g., with a simple vs a complex model, and across vs within etiological subgroups) may impact whether a significant treatment effect is detected.
Fey, M. E., Yoder, P. J., Warren, S. F., Bredin-Oja, S. (2013). Is more better? Milieu communication teaching in toddlers with intellectual disabilities. Journal of Speech Language and Hearing Research, 56(2), 679-693.
Fey, M. E., Warren, S. F., Brady, N. C., Finestack, L. H., Bredin-Oja, S. L., Fairchild, M., Yoder, P. (2006). Early effects of responsivity education/prelinguistic milieu teaching for children with developmental delays and their parents. Journal of Speech, Language, and Hearing Research, 49, 526–547.
Hart, B. & Risley, T. R. (1995). Meaningful differences in the everyday experiences of young American children. Baltimore: Paul H. Brookes.
Hoff, E. (2003). The Specificity of Environmental Influence: Socioeconomic Status Affects Early Vocabulary Development Via Maternal Speech. Child Development, Volume 74, Number 5, Pages 1368–1378
Hoff, E. (2013). Interpreting the language trajectories of children from low-SES and language minority homes: Implications for closing achievement gaps. Developmental Psychology, 49, 4–14.
Hoff-Ginsberg, E. (1998). The relation of birth order and socioeconomic status to children's language experience and language development. Applied Psycholinguistics, 19, 603–630.
Lifter K. Linking assessment to intervention for children with developmental disabilities or at-risk for developmental delay: The developmental play assessment (DPA) instrument. In: Gitlin-Weiner K, Sandgrund A, Schafer C, editors. Play diagnosis and assessment. 2nd ed. Wiley; New York, NY: 2000. pp. 228–261.
Warren, S. F., Bredin-Oja, S. L., Fairchild, M., Finestack, L. H., Fey, M. E., Brady, N. C. (2006). Responsivity education/prelinguistic milieu teaching. In: McCauley RJ, Fey ME, editors. Treatment of language disorders in children. Brookes; Baltimore, pp. 47–75.
Yoder, P., Woynaroski, T., Fey, M., & Warren, S. (2014). Effects of dose frequency of early communication intervention in young children with and without Down syndrome. American journal on intellectual and developmental disabilities, 119(1), 17-32.
-Liz Smith and Kari-Anne B. Næss -