Frank Wilcoxon, chemist and statistician, best known for the Wilcoxon-Mann-Whitney (rank sum) test and the Wilcoxon signed-rank test, two widely used nonparametric rank-based tests.

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21 views

Paired or unpaired Wilcoxon test?

I counted the number of geese on an intertidal mudflat on 100+ days over the winter. I made two counts on each of these days: one at low tide and one at high tide. I want to know if the number of ...
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1answer
44 views

Non parametric Wilcoxon Signed Rank test

I have the following data vector(in fact its 2392 data points long): ...
2
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1answer
31 views

Wilcoxon rank sum test methodology

I'm comparing the performance of two algorihtms $A$ and $B$ based on a metric. For each algorithm, I have $31$ independent samples that represent its performance. This samples are grouped in two ...
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22 views

Is pairwise wilcoxon test a valid non-parametric alternative to Tukey's HSD test?

I am trying to identify significant differences between groups from normal and non-normal distributions. When the distribution is normal the workflow is pretty straightforward: ANOVA and after that a ...
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29 views

Why do we assign fractional ranks in rank tests?

Both Mann-Whitney U test and Wilcoxon signed rank test follow this procedure: sort the data assign ranks, Ties receive a rank equal to the average of the ranks they span compute the statistic using ...
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17 views

Distribution heavily stacked on either limit - appropriate test?

I have two sets of results from an experiment that produces distributions with extremely heavily stacked sides and mostly uniform elsewhere. The aim of my analysis is to answer a the question roughly ...
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34 views

Difference between the Wilcoxon Rank Sum Test and the Wilcoxon Signed Rank Test using paired observations

I was wondering what the theoretical difference is between the Wilcoxon Rank-Sum Test and the Wilcoxon Signed-Rank Test using paired observations. I know that the Wilcoxon Rank-Sum Test allows for ...
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58 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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33 views

Adjustment of medians in the Siegel-Tukey test vs. the Wilcoxon test

I have two (unpaired) distributions. The distributions are far from being normal, so I'm using the Wilcoxon test to compare their medians: the Wilcoxon test does not reject the null-hypothesis ...
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29 views

Wilcoxon test to support logistic regression

I want to test the hypothesis that IV 2 (post-test value) is a better predictor for the criteria (no success vs. success) than IV 1 (pre-test value). Those IVs are indicators for static vs. dynamic ...
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29 views

what kind of non-parametric test to use?

I collected data on one sample, the DV could be separated into two groups (success yes vs. no) and then I have several IVs with interval scale. I just don't know if to use Wilcoxon or Man-Whitney ...
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2answers
65 views

Skewness adjusted t-stat

I've some data that is divided into a series of groups and am testing whether the mean is different from 1. The data is highly skewed, with skewness ranging from 1.10 to 26! I did a one-sample t-test ...
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16 views

Measuring treatment effect on top-ranked subjects selected at point in time from longitudinal data

I am trying to measure the effect of treatment after some time on a group of subjects who were selected for treatment because they were the highest (top 1200) ranked subjects during a single period ...
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73 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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75 views

Testing which groups have had a significant change

I have three groups with two hundred individuals each, and each individual within a group has a pre and post treatment measurement. A single group contains individuals with similar pre measurement ...
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1answer
159 views

Applying a post hoc Wilcoxon signed rank test to a Friedman when there are different sample sizes

I conducted a Friedman test to related-sample group in three conditions (pre-treatment, post-treatment and 6-month post treatment). Out of 216 participants that completed the first two stages, 50 of ...
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29 views

List of sample arrangements at a given Wilcoxon / Mann-Whitney test statistic

Consider a Wilcoxon-Mann-Whitney test statistic, either in the form (i) "W = sum of ranks in sample A"; or in the form (ii) "sum of ranks in sample A - the minimum possible sum of ranks in sample ...
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92 views

Is the W statistic outputted by wilcox.test() in R the same as the U statistic?

I've recently been reading about the Mann-Whitney U test. It turns out that to carry out this test in R you actually need to run a Wilcoxon test! My question: is the W statistic outputted by ...
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88 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 by two measurements of the same variable in a specific time (i.e. XYY [time, meas1, meas2]). This ...
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1answer
99 views

Wilcoxon one-tailed test

It's regarding a one-tailed Wilcoxon sign test. I am comparing (fictional) ratings of liking before and after a woman shaves off the hair. The design is complicated. I will do my best to explain. ...
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2answers
137 views

Should I expect a Z-Score as an output from a Signed Rank test?

I have some data that is highly skewed. I want to test whether the median of the data is different from 1, so I decided to use a Wilcoxon Signed Rank test. The description and implementation of this ...
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35 views

Which test should I run?

I have RNA sequencing data (= expression of a certain protein) from the lung tumor of 14 patients, 5 non-smokers and 9 smokers. If I want to compare the expression level of that protein of smokers vs ...
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1answer
450 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 ...
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1answer
137 views

Wilcoxon signed rank test on anonymous sample

I carried out a test on a group of 100 people. The test contained 10 questions with 5-point Likert scale answers (1 = Strongly Agree, 5 = Strongly Disagree). After the test was conducted, the group ...
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294 views

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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3answers
422 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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78 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. ...
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64 views

Nonparametric test for trend using Python

I am looking to perform a nonparametric test for trend on a continuous outcome across three groups, preferably in Python. For example height (pretend height is not normal) in 4th, 5th and 6th ...
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124 views

How to set confidence level for wilcoxsign_test (package coin)?

In R, the function wilcox.test takes the argument conf.level = 0.095 (for example). Giving the same argument to the function ...
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53 views

Test to rank methods by AUCs on various benchmarks

Suppose I have N methods and M benchmarks. I have an AUC statistic (and some other similar statistics) for each combination of method with benchmark. What test should I use to test if one method is ...
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41 views

Which of these two ways is better to report comparison of paired data?

Suppose I am comparing the computational time of two algorithms A and B. They are solving randomized problem P. Let's say I solved the problem for seeds $ 1, 2, \dots, n $ with both A and B and got ...
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218 views

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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46 views

Is Wilcoxon Signed Rank my solution?

A) I have: a pre and post measurement on 7 ordinal/scale variables for every participant (=student in classroom) 1 intervention 5 classrooms of students 3 teachers implementing the intervention I ...
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3answers
385 views

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 ...
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4answers
575 views

Testing for significance between means, having one normal distributed sample and one non normal distributed

I have following problem: Within an independent groups 1-factor design I have two independent groups, with a sample size of 20 each. The data of the treatment group is not normally distributed, ...
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1answer
79 views

Alternative to Wilcoxon signed-rank test, for data where many pairs are equal

I have several discrete datasets with a small range (-2 to +2) which I want to test against the null hypothesis "the distribution is centred around zero". The Wilcoxon signed-rank test was suggested ...
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60 views

Can I compare the p-values of two Wilcoxon tests?

I am comparing three distributions of values. Let's say A, B and C. If I find that the p-value of the Wilcoxon rank sum test between A and B is 1e-08 and between A and C is 1e-10, can I say that ...
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1answer
148 views

Evaluating software performance to identify regressions resulting from source code changes

I am attempting to monitor the performance of a software package in order to identify when a change to the code base introduces a performance regression (a slow down in the code). My assumption is ...
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74 views

What to input into Wilcoxon rank sum test when three pre and three post measurements are compared?

I have measured 23 patients three times pre and three times post treatment. Now I would like to see if the treatment had a significant effect. I thought about using a Wilcoxon rank sum test for this ...
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2answers
73 views

Prey preference - can I use a paired t- or wilcoxon test?

I have done an experiment in which I looked at the prey preference of an aquatic invertebrate. I used 10 containers all with one predator but with different densities of prey. I used two different ...
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24 views

Wilcoxon two-sample test approximated by z-statistic [duplicate]

I have two long vectors (both of the same size=12000 and each of them contains variance values). I want to perform Wilcoxon test to test if the variances in the first vector are different than the ...
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344 views

Different ways to calculate the test statistic for the Wilcoxon rank sum test

There are different ways to calculate the test statistic for the Wilcoxon rank sum test (quote from R help): The literature is not unanimous about the definitions of the Wilcoxon rank sum and ...
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1answer
1k views

Wilcoxon rank sum test in R

I have results from the same test applied to two independent samples: ...
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1answer
69 views

Share repurchase

I am doing a project for share repurchase in the US. I am trying to estimate the operating performance before and after the repurchase announcement. And I am trying to adjust the performance to the ...
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25 views

Testing that a finite quantity is equally partitioned

Suppose I have a set of observations on a finite (continuously divisible) quantity $Q$ (say $Q = 100$ to be concrete). For each observation $i$, $Q$ is partitioned into three parts $(A_i, B_i, C_i)$, ...
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174 views

Using Wilcoxon and Cliff's delta for comparing two sets of monitored variables?

I want to compare the following example vectors: a: [0, 1, 2, 3, 4] b: [4, 3, 2, 1, 0] a[i] represents a monitored variable ...
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2answers
174 views

What is the correct way of comparing two very small groups (N = 3)?

I have 3 samples of water contamination (bacteria/L) from a lake which I want to compare to another, more "pristine" lake. So I have 6 values in total, 3 belonging to each lake: ...
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1answer
276 views

Getting a zero p-value with Wilcoxon test in Matlab

I'm creating a classification model for detection of stress. I'm trying to select the best features from 56 total. I have a matrix of 1937x56 with the non stress ...
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204 views

Wilcoxon signed-rank test. Is it necessary?

I have a sample with millions of points. Every point $x$ has two values associated, let's say $A_{x}$ and $B_{x}$. I calculated the mean values of A and B in the sample: $\overline{m}_{A} = 0.19 ...
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91 views

Error in scipy Wilcoxon signed-rank test

I was digging in the scipy code for this test Wilcoxon signed-rank test (stats.Wilcoxon) and I found that in scipy they compute the sum of the ranks for the differences that are positive and ...