# Tag Info

Accepted

### Non-parametric test if two samples are drawn from the same distribution

The Kolmogorov-Smirnov test is the most common way to do this, but there are also some other options. The tests are based on the empirical cumulative distribution functions. The basic procedure is: ...
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### When should I use scipy.stats.wilcoxon instead of scipy.stats.ranksums?

Frank Wilcoxon's 1945 paper  described two tests -- for "Unpaired Experiments" and "Paired Comparisons" which have come to be called the (Wilcoxon) rank sum test and the (Wilcoxon) signed rank test ...
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### Paired t-test with multiple observations per pair

Averaging the data will result in a loss information and statistical power, so it is best avoided. Since you have repeated measures for websites, you can account the differences between websites (or ...
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### If the difference of scores is normally distributed, the sample distributions don't matter in a paired t-test, right?

You are correct. A paired t-test is conducted on the differences of the paired scores. It doesn't look at the individual scores in any way. A paired t-test is precisely the same as a one-sample t-test ...

### Wilcoxon signed rank test – critical value for n>50

The Wilcoxon signed rank test has a null distribution that rapidly approaches a normal distribution. The tables tend to stop by n=50 because the normal approximation is excellent well before that ...
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### How to choose between sign test and Wilcoxon signed-rank test?

I am trying to pick one from these two tests to analyze paired data. Does anyone know any rules of thumb about which one to pick in general? The signed rank test carries an assumption about symmetry ...
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### Wilcoxon Signed Rank Symmetry Assumption

Although on the surface the two statements above may appear contradictory, they aren't. The Wilcoxon Signed Rank test does require that the paired differences come from a continuous symmetric ...
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### Wilcoxon signed-rank test null hypothesis statement

This answer has been revised after being accepted, as I did not adequately appreciate Wilcoxon's critique of the sign test to extend the null hypothesis. I address the difference between the revised ...

### Same p-value. Is it normal?

Wilcoxon signed-rank test just takes in account the signs of the differences of values of every pair of data, and it doesn't take in account how large is such a difference. Therefore, the only thing ...

### Wilcoxon Signed Rank Symmetry Assumption

Note that the samples may tell you nothing about the suitability of the assumption that is required for the null. If the null is false, you don't necessarily require symmetry (and it's easy to ...

### Questions about Wilcoxon signed rank test

An excellent question. As @Glen_b implied, the signed rank test, unlike the Wilcoxon unpaired 2-sample test, is metric-dependent. A better test is the Kornbrot rank difference test discussed here. ...

### How to perform a Wilcoxon signed rank test for survival data in R?

To answer your question on how to calculate this in R, you can use the comp() function from the survMisc package. Example: <...
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### Wilcoxon signed-rank test in R

R reports the V-statistic, which is the sum of the positive ranks. The Wikipedia example computes it slightly differently, as the sum of all ranks, regardless of sign. In other words, both versions ...

### Statistically Comparing the Similarity Between Lists (e.g Food Preferences)

Rearranging the data so the foods are in the same order (John's), I got the following vectors, each of 12-counts (you should proofread them): ...

### Creating a reference group to have equal sample sizes for Wilcoxon signed rank test

The Wilcoxon signed-rank test, made almost obsolete by the rank difference test is only for naturally paired data. You do not have paired data but rather data more suitable for the Wilcoxon Mann-...

### Questions about Wilcoxon signed rank test

A signed rank test relies on taking pair differences. Consequently you're asserting that the difference between a 1 and a 3 on a corresponding pair of Likert item is the same as the difference ...

### Effect size to Wilcoxon signed rank test?

If you don't have ties, I would report the proportion of after values that are less than the corresponding before values. If you do have ties, you could report the proportion of after values that ...
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### normality for extremely small sample N=5

You can't make much of a distributional assessment at n=5 -- you can (sometimes) see non-normality at n=5 -- but at such small sample sizes the non-normality has to be quite strong to have a good ...
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### Wilcoxon signed rank test fails for small sample size

The Wilcoxon sign-rank test is a nonparametric test for difference in ranked differences between two groups. Let's take that apart: Wilcoxon: He gets the credit for developing this test. sign-rank: ...
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### Effect size for Wilcoxon signed rank test that incorporates the possible range of the attribute

The effect size statistic Z/sqrt(N) --- sometimes called r --- in the paired observations case, is related to the probability that one group is larger than the other, or if you'd rather, that the ...