I am working on the assumption page of the Wilcoxon signed-rank test (the wilcox "paired test") in Wikipedia.
I was able to locate a reference for the assumption that I wrote there, which are:
Let $Z_i=X_i – Y_i$ for $i = 1, \ldots , n$.
- The differences $Z_i$ are assumed to be independent.
- Each $Z_i$ comes from the same continuous population, and is symmetric about a common median θ .
- The values which $X_i$ and $Y_i$ represent are ordered (at least the ordinal level of measurement), so the comparisons "greater than", "less than", and "equal to" are useful.
However, I get this nagging feeling that I am missing something here. Can anyone correct/expand on this?