Applying the phonological intervention taxonomy to expansion points intervention.

Purpose: The Phonological Intervention Taxonomy (Baker, Williams, McLeod, & McCauley, 2018) was developed on the basis of cataloguing the elements of 15 phonological interventions in the domains of the goal of intervention, the teaching moment, the context (who provides the intervention and where it is provided), and procedural issues. Additionally, three summary measures are computed from the tallying of elements in the taxonomy: concentration (the number of required plus optional elements, with a maximum of 72; flexibility (the number of optional elements compared to the total present for the intervention), and distinctiveness (the number of rare elements plus the number of common elements that are absent). In the present paper, the taxonomy is applied to a novel intervention called Expansion Points Intervention (EXP; Smit, Brumbaugh, Weltsch, & Hilgers, 2018) in order to (a) determine how well the taxonomy captures elements of EXP, and (b) compare EXP to other phonological interventions.

Method: The four domains of the taxonomy were systematically applied to EXP to determine which elements were required, optional, or not relevant to the implementation of EXP, using the definitions supplied with the taxonomy.

Results: Of the 72 elements in the taxonomy, 25 were considered required elements in EXP and 15 were considered to be optional, resulting in a concentration of 40 and a flexibility of 37.5 %, both of which were in the lower part of the range for the 15 comparison interventions. By way of contrast, distinctiveness, at 15 % was at the high end of the range.

Conclusions: Based on the ease with which EXP aligns with elements of the taxonomy, the taxonomy was readily applied to EXP. EXP appeared to be comparable to the 15 original interventions, which means that the principles underlying EXP resemble those of other interventions. The implications of these findings for a theory of therapeutic intervention for phonological disorders are discussed.