Editor's Note:
The following article is one of 38 thought-provoking essays found in Thinking About Child Language, a 2006 release written by Judith Johnston and available from Thinking Publications University (a division of Super Duper Publications www.superduperinc.com). In her essays, Judith Johnston summarizes research on a topic of clinical relevance and then follows each summary with a commentary and discussion of the clinical application. Each essay captures Judith's reflections and thoughts on everyday challenges of language intervention and is an invaluable resource for speech-language pathologists.
Evidence? What Evidence?
There is much talk about evidence-based practice in the SLP literature these days. Initially, this phrase brought to mind stories about the emperor's new clothes and tempests in teapots. Of course we should base our practice on the evidence, and we do. So what's all the fuss? I have to admit, however, that the more I think about this topic, the more interesting it becomes. The real question is not whether we should base our practice on the evidence, but rather what sort of evidence should we use? And where can we find it?
What Sort of Evidence?
I'll begin with the first question: What sort of evidence should we use? Good evidence is evidence that
- comes from studies with strong designs,
- can be readily interpreted, and
- is up-to-date.
An Oxford study of physicians' treatment decisions indicated that some 82 percent were supported by this sort of high quality evidence (Ellis et al., 1995). How well do we do?
Strong Evidence
Evidence about a clinical practice can be graded according to its strength, that is, according to the degree to which it can reliably indicate that a practice has an effect, and that this effect can be replicated and generalized. Table 2.1 on page 10 ranks various research designs according to the strength of the evidence they yield, in descending order of strength.