Clinical Significance – CASP
To understand results of a trial it is important to understand the question it was asking.Key Concepts addressed:
In a systematic review of riluzole for amyotrophic lateral sclerosis done for NIHCE, the authors found a marginally statistically significant result suggesting an improvement in functional status associated with riluzole, with p-values ranging from 0.03 to 0.07 for the pooled results from the three different measurement scales reported in the trials. This was the first time any evidence was published suggesting a statistically significant improvement in functional status because, in their representations to the regulatory authorities, the company had not pooled the results of all the trials for these outcomes and the drug was licensed to extend tracheostomy-free survival only.
Despite this new finding, there is still a considerable question mark over the clinical significance of these results. The improvements observed were very small, just one or two points on scales which might have a maximum score of 80 or 100, and which measure “fuzzy” things like the ability to grip a pencil. It is certainly encouraging to find that there might be an improvement in functional status to go with the likely improvement in survival, but it is important that someone who is considering taking riluzole is given clear information about the likely size of the benefits, and the likelihood of harm due to side effects, before making a decision about treatment.
Statements like “the difference in means was 2.7 (p=-.023)” or “RR=1.6 (p=0.044)” don’t mean anything to real people, and they might be misleading to the clinician. They need to be translated into clinically meaningful terms before we can assess whether the benefit offered is worth the costs. We will look at a simple means to do this in the next two sections, but first we will discuss another important consideration: what was the comparator?