[R] Clinical significance - Equivalence test

[Marc Schwartz]

On Mar 27, 2014, at 8:53 AM, Manuel Carona <unkuiri at gmail.com> wrote:

> Hi,
> 
> I have implemented a therapeutic intervention on two groups (one is a
> control group) and tested them in two moments using some assessment
> tools (with normative data). Now I want to compare the experimental
> group with the control group using clinical equivalence testing. To do
> this I need to specify a range of closeness (One for each assessment
> tool according to the specificity of this same tool) and do two
> one-tailed tests to test if the two groups are considered clinically
> equivalent in the first moment and on the end I want to compare the
> experimental group with the normative data (Here I have to add the mean
> and standard deviation of the normative sample because I don't have the
> normative sample).
> 
> I know that R has a package named equivalence but I don't know how to do
> this kind of calculations with it. Is it even possible with the actual
> packages?
> 
> Thanks in advance


I have not used it, but a quick review of the documentation the 'equivalence' would suggest that at least the tost() function might be what you need.

The being said, you may need to seek the assistance of a local statistician familiar with the methods and underlying theory to guide you, beyond simply performing the analyses. 

It is not clear from your description above if the two time points are a baseline and post-treatment pair for each subject, or if they represent 2 time points beyond baseline (3 measures per subject), which would make this a repeated measures scenario and more complicated. In addition, with multiple assessment tools, what multiple testing adjustments may be required to control the likelihood of Type I errors?

If this is a formal study, with a powered a priori hypothesis, all of this should have been pre-specified in the study protocol in the statistical analysis section (and possibly in a stand alone statistical analysis plan) by someone familiar with study designs of this type and the appropriate analytic methods.

There are also regulatory guidance documents (eg. FDA) and books that cover the design and analysis of bioequivalence studies and those should have served as a reference for such a study design.

Again, seeking local expertise would seem apropos here.

Regards,

Marc Schwartz