nonparametric tests

Hi, I did experiment to compare the effect

Hello all, I've been asked to assist with the statistical analysis of some survey data, and I'm a bit of a novice with this type of analysis, so I'm hoping that some with more experience can give me a bit of guidance. The investigators are interested in assessing the effectiveness of 6...

I'm pretty confused about the conditions in which I should use a parametric or a nonparametric test to compare the means of 2 (or more) populations and would be very grateful if someone would explain it to me. I know that if the distribution of the sample is not normal, non-parametric...