I have species abundance (different sp.) data collected from 6 sites at two different seasons. I want to test if there is seasonal variation in the bundance of species by using the Wilcoxon signed-rank test (paired data). Can anyone help me?
Sign test is best to use when we have two variables their observations are yes or no, + or - . If you have sis sites for two seasons and you have repitions or replicates ,you better use factorial or split plot as you suggest you look to your variables. Regards.
Mengistu Wale The Wilcoxon rank-sum method compares two independent samples, whereas the Wilcoxon signed-rank test is used to compare two related samples, matched samples, or to do a paired difference test of repeated measurements on a single sample to see if the population mean ranks differ.
It is used to compare two sets of results from the same individuals. This might happen when we want to look at any changes in scores from one point in time to the next, or when individuals are subjected to more than one condition.
If the data is non normal as it seems to me then you may use the non parametric test Mann Whitney U Test to see whether there exists any significant difference in the variation between the two seasons. However, if the number of seasons being observed is more than two then one should go for the Kruskal Walllis H Test.
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