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