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.
References:
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 -
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