How to sort search results from SCOPUS or Web of Knowledge by number of citation in a specific field?
There is no automatic solution to this - it is an extremely time-consuming labour, sometimes performed by bibliometricians - and often only by those with access to full editions of either database (not the web-interfaces, with strict limitations to download sizes).

It is also a tricky subject, as the defionition of e.g. a statistics paper may differ from what you are actually looking at: journal categories. Papers on any topic are also published in journals not directly related hereto, there are plenty of translational and multi-disciplinary journals as well - in other words, what may appear to be a trivial task is actually very complex.