Dose Frequency for Effective Speech Therapy

I am writing to address a specific question that has come up: in order to be effective when treating an “articulation disorder” how many trials should the SLP elicit from the client per treatment session? This is an important question and it is surprising that so little research attention has been directed at uncovering the answer. This is a question about what Warren, Fey and Yoder (2007) refer to as “dose: number of properly implemented teaching episodes per session”. We could be talking about the number of presentations of a model or perceptual responses by the child when conducting an “input oriented intervention” but in this blog I will restrict my comments to those interventions that are focused on obtaining speech responses from the child and therefore the teaching episode involves practicing a speech behavior such as a sound, syllable, word or phrase and each elicitation is counted as a single dose. In speech therapy the question of optimum dose frequency (how many trials per session of a given length) comes up most often in the context of Childhood Apraxia of Speech (CAS) where it is generally believed that practice intensity is particularly important. Recently, Murray, McCabe & Ballard (2014) reported that studies on approaches for CAS typically involved 60 to 120 trials per session whereas studies on approaches for phonological disorders typically involved 10 to 30 trials per session. The closest I have seen to an experimental investigation of dose frequency is the single subject experiments conducted by Edeal and Gildersleeve-Neuman (2011) in which low intensity (30 to 40 trials/session) versus high intensity treatment (100+ trials/session) was compared within two children with CAS. They concluded that “Both children showed improvement on all targets; however, the targets with the higher production frequency treatment were acquired faster, evidenced by better in-session performance and greater generalization to untrained probes.”

I don’t see any reason why a higher intensity intervention would not also be a “good thing” when treating children with a phonological disorder and indeed this is what Williams (2012) concluded when she reviewed data from her lab. After a quantitative summary of treatment outcomes for 22 children who received her multiple oppositions intervention she recommended a minimum dose of 50 trials over 30 sessions with anything less being ineffective and higher doses (70 trials or more) being necessary for the most severely impaired children. In this case the children received 30 minute sessions twice per week.

Recently we have been conducting single subject experiments with children who have CAS and although treatment intensity is not the primary focus of attention in these studies my doctoral student, Tanya Matthews, and I have been looking at the relationship between dose frequency and outcomes. In the figures shown below the children’s “next day probe scores” (an indicator of maintenance of learning over a short-term period, expressed as proportion correct) are shown as a function of the number of trials completed (top chart) as well as the number of correct trials in each session (bottom chart). There is not much variability in the number of trials per session because we put a lot of pressure on the student SLPs to keep this number high. However the number of correct trials varies quite a bit depending upon the severity of the child’s speech delay and whether it is early or late in the child’s treatment program. The lower chart shows that next day probe scores are better if the number of correct trials in each 20 minute practice session is above 60. The number of correct trials never goes above 80 because we are working to keep the child “at challenge point” so if the child begins to produce more than 80% correct trials we make the task more difficult. However, if the child is producing many errors it does not really help to keep the response rate high either because the child is just practicing the wrong response anyway.

So to sum up, notwithstanding the rather poor quality and quantity of the data, my impression is that dose counts: regardless of whether the child has a motor speech disorder or a phonological disorder it is important to achieve as many practice trials as you can in a treatment session but it is also a good idea to ensure that the child is achieving accuracy at the highest possible level of complexity and variability during practice as well.

Number of trials by probe score

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7 Comments

  1. Donna Thomas

     /  July 10, 2014

    Thanks for your very interesting post – such an important consideration for both phonology and CAS. I really enjoy reading your blog and thinking about the research and clinical implications of the things you discuss. I note that you use the term dose frequency to describe the number of trials in a session. At the University of Sydney we’ve been doing some work with CAS looking at dose frequency – but rather than investigating the effect number of trials per session we’ve been investigating the effect of frequency of sessions. We’ve got an article in press about a lower dose frequency of ReST treatment for CAS, where children had therapy twice a week instead of the previously reported four times a week. Definitely an interesting area!

    Reply
    • Hello Donna,

      Thank you for your comment, yes that is another issue again, I look forward to reading your paper (I am on “vacation” so it will be awhile before I get to it. But I am pleased to see another paper on that topic. Susan

      Reply
  2. Interesting post. I think about this frequently, especially with children who are more resistant to repeated practice due to either personality type, increased awareness/embarrassment, or concomitant diagnoses. A solid bank of data would be so nice in this area, both for treatment efficacy and explanation of variable rates of progress to families/caregivers. Thanks for shedding some light!

    Reply
    • Thank you for your comment Ashley. This study is about CAS specifically so we are demanding high response rates but in a previous study targeting children with phonological disorders we found that we could have equally good results with an input oriented approach in which the children were not required to practice much speech at all. Rather the emphasis was on listening to speech and making judgements about the accuracy of the clinician’s speech or responding in a functional or pragmatically meaningful way during conversations in which the clinician might present phonological contrasts. Speech production practice was required only when the child indicated that he or she was ready. This approach was especially effective with children who were resistant to practice for the reasons that you mention. Dose frequency remains an important concept but in this case the clinician must present a high frequency of input forms.

      Reply
  3. Ottilia

     /  December 18, 2017

    Hello. I would like to enquire about the frequency, in terms of number of times per week. I know its case to case depending on the condition of the patient. But what is the acceptable average number of times a week?

    Reply
    • Hello Ottilia,

      Thank you for your interesting question. This is an issue that has received insufficient research attention as Francoise and I point out in our book. It does appear to us that it is possible to provide therapy at a dose frequency that is too low to provide a significant benefit (as described in the Glogowska et al trial for example in which approximately 6 monthly visits by the family to the clinic resulted in outcomes not much better than “watchful waiting”). On the other hand, for the average child with developmental phonological disorder it is possible that you will reach a point of diminishing returns if you have too many sessions in a week because the amount of improvement that you can obtain will be limited by developmental factors and the amount of authentic practice in the home and school environment that is required for generalization and maintenance. That being said there is one published study on dose frequency in phonology therapy: Allen, M. M. (2013). Intervention efficacy and intensity for children with Speech Sound Disorder. Journal of Speech, Language & Hearing Research, 56(3), 865-877. doi:10.1044/1092-4388(2012/11-0076)

      Allen, using the multiple oppositions approach, obtained better results when the children received 24 treatment sessions scheduled 3 times per week over 8 weeks compared to when children received 24 treatments session schedule 1 time per week over 24 weeks. This result might be particular to this treatment approach however.

      I noticed that the increase in PCC in Allen’s study was not particularly impressive, about 4 to 6 percentage points (I think, it is hard to tell because post test scores were adjusted for pretest scores). As I reported in a recent blog, “How effective is phonology therapy” I observed large variations in effectiveness depending upon the details of the type of treatment and the implementation of the treatment. So for example, when a behaviorist approach was used with no home program we observed only a 2 point gain in overall PCC (despite large effects for treated stimulable phonemes). In another study we obtained a 14 to 19 percent gain in correct production of difficult phonemes when a phonological approach was implemented with a speech perception training component and parent involvement. In both of these studies the intervention was only once weekly. Specifically, the results reported in that blog for Rvachew, Nowak and Cloutier (2004) suggest that once weekly can be sufficient for many children because that group achieved an excellent gain in PCC and age appropriate speech by school entry.

      Therefore my conclusion is that if you are treating a child at least weekly you can often obtain a good result. If you are not observing reasonable gains with weekly therapy, it is not advisable to increase dose frequency in order to simply do “more of the same”. If on the other hand you are sure that you are employing the most effective procedures with the child, and the parents or funders can afford it, more is better up to the limit of no return is probably a good maxim. Unfortunately we have not established what the limit of no return is yet using appropriate scientific procedures.

      Thank you again for your question. Susan

      Reply
  1. Worth Repeating: Dose Frequency for Effective Speech Therapy | PediaStaff Pediatric SLP, OT and PT Blog

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