Are the two groups independent? if yes use mann-whitney, if not use Wilcoxon. Do you know SPSS? If not and you want to do Wilcoxon, go here: http://www.scribd.com/doc/2985277/St...cs-using-Excel. On the last pages it describes how to conduct Wilcoxon for paired data sets. If you still have any other questions, send an email to the address written on the first page of statistics using Excel.