Hi @DoEDorkily123 : I assume you mean Relative Standard Deviation (100*[Sample SD/Sample Mean]). There is no reason it can't be a response. Generally speaking, any statistic (function of your data) could be a response. That said, RSD will not have a normal distribution; it tends to be skewed right so often a log (natural log) transformation is often used to make it approximately normal so that you can use the most common types of analyses (which assume normality); there is no guarantee that the log transformation will be appropriate (or even necessary), but in my experience it often is.