Stats: is a set of values within a normal range?
February 12, 2013 3:58 AM Subscribe
I'm trying a analyse a set of biological data for a research project and I'm having trouble finding the appropriate statistical tests to use.
posted by snoogles to science & nature (3 answers total)
3 time points with levels of an immunoglobulin (Ig) for n patients
Day 1 n=23
Day 2 n = 23
Day 3 n = 14
I've run a D'Agostino and Pearson normality test for each time point, and some are normal and some not.
I know what the range and median levels of the Ig are for healthy patients. I want to know 2 things:
a) at each time point, if the levels I have are significantly different from health
b) if the levels of the Ig are significantly different between time points
A previous paper with similar data used a Wilcoxon Signed Rank test using the median levels for healthy patients as the "theoretical median" to answer a).
1) Is the Wilcoxon Signed Rank test indeed the right test to answer a)?
2) Should I use the Wilcoxon even for the sets of data which are normally distributed?
3) What does it mean when the p-values for the Wilcoxon are either exact or Gaussian estimates?
4) Which test do I use to answer b)? My software suggests the Friedman test for repeated measure non-parametric, but won't run it because I'm missing some values for Day 3.
Please help! This type of stats is beyond what the other people in my lab are familiar with...