# Questions tagged [wilcoxon-signed-rank]

a non-parametric rank test to compare two paired samples, whether values in one are bigger than in the other. This test is NOT the same as the sign test.

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### What is the difference between the Wilcoxon Rank Sum Test and the Wilcoxon Signed Rank Test?

What is the difference between the Wilcoxon Rank-Sum Test and the Wilcoxon Signed-Rank Test using paired observations? I know that the Rank-Sum test allows for a different number of observations in ...
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### Non-parametric test if two samples are drawn from the same distribution

I would like to test the hypothesis that two samples are drawn from the same population, without making any assumptions about the distributions of the samples or the population. How should I do this? ...
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### Effect size to Wilcoxon signed rank test?

Some authors (e.g. Pallant, 2007, p. 225; see image below) suggest to calculate the effect size for a Wilcoxon signed rank test by dividing the test statistic by the square root of the number of ... 27k views

### Wilcoxon rank sum test in R

I have results from the same test applied to two independent samples: ... 5k views

### Why is the asymptotic relative efficiency of the Wilcoxon test $3/\pi$ compared to Student's t-test for normally distributed data?

It is well-known that the asymptotic relative efficiency (ARE) of the Wilcoxon signed rank test is $\frac{3}{\pi} \approx 0.955$ compared to Student's t-test, if the data are drawn from a normally ...
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### How to find out if an online poker-site is fair?

Last week I had an interesting discussion with a good friend of mine. He had been playing some online poker and suggested that there is a relationship between new subscription/additional money ...
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### Repeated measures over time with small $n$

I was given data to analyze for a study looking at the effects of a treatment on iron levels at four different time points (before treatment, the day treatment ended, 4 weeks after treatment, and 2-4 ...
42k views

### Paired t-test for binary data

I have one sample with n=170 and two binary variables (A,B) that can take as a value 1 or 0, where 1 counts as a success and 0 counts as a failure. What I want to know is whether the means of these ...
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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?
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### In what situation would Wilcoxon's Signed-Rank Test be preferable to either t-Test or Sign Test?

After some discussion (below), I now have a clearer picture of a focused question, so here is a revised question, though some of the comments might now seem unconnected with the original question. It ...
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### Is ordinal or interval data required for the Wilcoxon signed rank test?

Having looked at multiple online sources, I can't seem to get a straight answer. Could someone please clarify for me if ordinal data is sufficient to use for the WSRT and if not, is the sign test an ...
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### How is the confidence interval built when executing the Wilcoxon.test in R?

I want to calculate the confidence interval around the median obtained from this data set: ...
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### How to perform a Wilcoxon signed rank test for survival data in R?

Say you have survival data like this: ...
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### How to compute the power of Wilcoxon test?

I am using Wilcoxon test to compare two paired sets of data for whether their means differ. Besides the p-value, I would also like to know the power of this test. How to compute it in R? Thank you in ...
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### Wilcoxon Signed Rank Symmetry Assumption

The assumption of symmetricity for signed rank test (and its relevance) is becoming extremely confusing for me. I am hypothesizing that sub-population A (before treatment) and sub-population B (after ...
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### How to best visualize one-sample test?

We are currently writing a paper with several one-sample Wilcoxon tests. While visualizing two-sample tests is easy via boxplots, I was wondering whether there is any good way to visualize one-sample ...
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### Relative efficiency of Wilcoxon signed rank in small samples

I have seen in published literature (and posted on here) that the asymptotic relative efficiency of the Wilcoxon signed rank test is at least 0.864 when compared to the t test. I have also heard that ...
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### Alternative to the Wilcoxon test when the distribution isn't continuous?

One of the assumptions for using the Wilcoxon sign-rank test is that the underlying distribution is continuous (see here.) However, there are cases (for example, when analyzing Likert scale data) ...
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### When should I use scipy.stats.wilcoxon instead of scipy.stats.ranksums? [duplicate]

I've been using http://docs.scipy.org/doc/scipy/reference/generated/scipy.stats.wilcoxon.html but then I realized that there is http://docs.scipy.org/doc/scipy/reference/generated/scipy.stats.ranksums....
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### If the difference of scores is normally distributed, the sample distributions don't matter in a paired t-test, right?

I have a very straight-forward question: If the difference of scores is normally distributed, the sample distributions don't matter in a paired t-test, right? Therefore, If the samples are not ...
929 views

### Rank and z-transform instead of Wilcoxon?

Andrew Gelman in a recent post in his blog suggests using a rank, transforming the rank to a z-score, and then using parametric tests and tools instead of performing non-parametric tests. I never ...
6k views

### What method is preferred, a bootstrapping test or a nonparametric rank-based test?

I want to perform a single-tail test on a single sample of real numbers (N~100) against an expected value. The population is known to be not normally distributed. So from what I've read about stats, I ...
7k views

### Why do zero differences not enter computation in the Wilcoxon signed ranked test?

The Wilcoxon signed ranked test tells us if the median difference between paired data can be zero. The test is executed by computing a statistic, then a z-score and comparing it to a critical value. ...
4k views

### Can I use Wilcoxon Signed-Rank Test to test pairs of data in a time series?

I have a dataset of measurements (non-normally distributed). Each line of this dataset is composed of two measurements of the same variable at a specific time (i.e. XYY [time, meas1, meas2]). This ...
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### How to interpret the estimate from Wilcoxon signed rank paired test?

Suppose I do a Wilcoxon signed rank paired test such as: ...
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### Appropriate tests on discrete and paired data

I am going back and forth on which tests to do. I have two paired variables, that are both positive integers (0,1,2,3...etc). $n = 559$. The variables represent the error resulting from two different ...
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### Questions about Wilcoxon signed rank test

I wanted to conduct a Wilxocon signed rank test but stumbeld upon two questions that I am unable to solve on my own. I tested 2 types of interfaces for a software with the same ten people. I want to ...
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### Paired t-test with multiple observations per pair

I have a bunch of websites websiteA....websiteZ for example. Now I have an optimization technique that possibly improves the performance of these websites. I want to check whether this technique ...
32k views

### Large difference between Mann-Whitney test and Wilcoxon signed rank test significance

I am looking at a success of textual requests. We have a dataset of matched pairs, one successful, one not successful, and they are matched based on length of the request in words (since I want to ...
950 views

### Bonferroni correction for two different tests on the same dataset

I am having trouble figuring out the correction factor to choose for a Bonferroni correction. Let me explain. I have two datasets, control ($x$) and data from left ($y_1$, affected limb) and right ...
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### Test whether two rank orders differ

I have 20 human subjects doing a task under 2 different difficulty conditions. (So it's a repeated measures design) Each person has a different performance in each of the task difficulty conditions, ...
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### When is it appropriate to use a paired Wilcoxon test?

Could someone please explain in plain English (preferably without using the word paired) or by using examples when it is appropriate to use ...
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### Wilcoxon signed rank test – critical value for n>50

I have seen that someone has asked a similar question a few years ago, but unfortunately the answer is not helpful. I am in the process of estimating a Wilcoxon signed rank test with a n=63 by hand. ...
15k views

### z score on Wilcoxon signed ranks test?

I was wondering if anyone might have some answers to a question regarding running a Wilcoxon signed rank test in R. When looking up how to report our scores, it tells us to report a Z score. However,... 1k views

### Use of Wilcoxon test for non-normal data akin to Two One Sided T-test

I'm analysing paired data for equivalency and it's not normally distributed, i.e., the difference of the paired result is not normally distributed due to, amongst other things, outliers. If it were ...
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### wilcoxon signed rank test to test paired data?

I want to test whether the difference between the pairs of students's scores follows a symmetric distribution around zero.See below ...
11k views

### Wilcoxon-signed rank vs Kruskal-Wallis?

I am rather stressed out about my methodology. For my PhD I ran a year long literacy intervention (small scale longitudinal study) that was supposed to test the rate of change in individual students' ...