# Questions tagged [wilcoxon-mann-whitney]

The Wilcoxon rank sum test, also known as Mann-Whitney U test, is a non-parametric rank test to assess whether one of two samples has larger values than the other.

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### Two-sample test when samples are not completely independent?

Let's say I measure the height of 100 individuals every week in both Illinois and Texas while allowing for the same individual to be measured multiple times in the following weeks. This way, my ...
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### How to calculate a single threshold value to measure the mean differences are meaningful?

I have a dataset with two groups: Region A (N=3980) and Region B (N=880). The dataset is very simple which has a measurement from a sensor. The values are generally very small. I then performed Mann-...
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### Which test to use for this scenario?

A histogram of white blood cell (WBC) counts in 15 sick patients showed that the distribution was negatively skewed. If we wanted to test for differences between the published WBC count for a healthy ...
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### Can rankFD() handle within subjects variables?

I got a recommendation to use a non-parametric alternative to an ANOVA. I've got two within subjects variables and one between subjects variables. The suggestion was to use rankFD() to do the test, ...
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### How to interpret a large Cohen's d when p-value is non-significant and CI's are close to 0

I have a sample size of 23, with 11 and 12 participants in each group. I conducted t-tests for several continuous dependent variables. All of them are non-significant, but some of them have quite high ...
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### How to test that a discrete time series has markovian properties? How to use the Wilcoxon test to do so?

Let us assume I have a time series made of the following observations: ts = c(163,18,53,189, 243, 101, 150, 39, 60,96,36,76,71,67,56,3,72,96,15,19) How can I use the Wilcoxon test to determine if it ...
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### Comparing two groups with non-negative integers?

Can I use Mann Whitney U Test (Wilcoxon Rank Sum Test) to test for differences between two populations for count data (i.e. non-negative integers)?
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### Comparison of different statistical tests on different amount of biological replicates

I am testing differentially expressed genes using different statistical tests on different amount of biological replicates (Wilcoxon test, t-test and negative binomial test). Figure below is what I ...
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### Kruskal-Wallis and Mann-Whitney U give different results

For my thesis, I am comparing the importance of "comfort" (measured using a 6-point Likert scale) among four groups of people (participants who prefer traveling by plane, by train, by coach ...
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### Relevant statistical test for data of a ranking experiment

I'm currently thinking of a relevant statistical test to use to assess the results of a small study. Imagine i have 6 different brand of a food product and i want to know whether the participants to ...
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### Mann-Whitney U Test and Independent t-test give different results, which to use?

I have two population and I want to know if the means of the two populations are different. To the best of my knowledge, I should try an Independent t-test if the data is normality distributed and ...
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### Can someone explain the nuance in the wilcox.test function?

This is from a homework assignment for my grad stats class. First I generate a dataset: ...
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### Estimating distribution of tied ranks for tie correction to Wilcoxon-Mann-Whitney U test

Tests based on ranking elements, such as Mann, H. B.; Whitney, D. R. On a Test of Whether one of Two Random Variables is Stochastically Larger than the Other. Ann. Math. Statist. 18(1):50-60, 1947, ...
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### Statistical Test to Compare Count Data

I need to compare two vectors containing count data with different sample sizes. The example problem is the following: I have experiment on two groups of people that eat some number of apples until ...
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### Mann whitney and boostrap confidence intervals provide contradictory results

We are doing some a/b testing and have non-normal metrics so our typical t-test aren't appropriate. I typically use bootstrap CI and/or Mann whitney tests to determine the true effect. In this case ...
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### Interpreting Wilcoxon rank sum test results

I have Likert scale data (283 observations) from two groups are I'm trying to interpret the results of a Wilcoxon rank sum test, not being a statistician. ...
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### Interpret results from Mann Whitney pairwise hypothesis test in R

I have run ten runs of cross-validation in R for four models, and I have then computed an RMSE error measurement on each run of each model. First, I used ...
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### Non-parametric test for station variation

Certain disease reduces the concentration of calcium in people's blood. To test the effectiveness of a drug for the treatment of the disease, 9 individuals with the disease underwent an assessment in ...
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### Comparing salaries of people doing the same job

How do you compare salaries of two groups (male and female) of workers doing the same job, in order to see if there is a statistically significant difference between their pay? I've been reading ...
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### Change over time between two groups and within groups - Mann Whitney or Kruskal Wallis?

I have two groups (Control and Disease) and for each group a variable y is measured at three time points (0H, 24H, 48H). I want to know two things: Does y change between Control and Disease at each ...
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### Is there an algorithm with linear time complexity to calculate the rank sum statistic?

Definition 1: For a real array $x = (x_1, \dots, x_n)$, denote the rank of $x_i$ in $(x_1,\dots, x_n)$ by the following:  r_{i}=\sum_{j=1}^{n} I_{\left(x_{j} \leq x_{i}\right)}, \quad 1 \leq i \leq ...
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### Ranked t-test or Mann-Whitney U test for commerical A/B testing

Please help me understand how this blog post relates to this experiment. Here I try to reproduce quite old paper from Zimmerman about Mann-Whitney U test and ranked t-test (and also plain t-test) ...
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### Mann-Whitney test for unequal sample sizes

I want to run a Mann-Whitney test. But I got to know to know that for sample more than 20 we need to apply a different formula. My data sample is as follows. Group A contains data of 4 people and ...
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### T-test or Wilcoxon for small sample paired data

I have metabolomics data, I only have 5 paired samples. the data does not follow a normal distribution so instead of doing a t test I was thinking of doing Mann Whitney Wilcoxon (MWW) test but I have ...
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### Consequences of violating assumption of equal variance Mann-Whitney U test for location shift model

I've read through several posts on the WMN test, but can't seem to find information on this question. What are the consequences if one assumes equal scale in distributions for a location shift model ...
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### Using an old trained model on a new data - comparing two populations

I have two populations with the same set of features. The range of the features' values is also the same. I trained Random Forest Algorithm on the first population. Thus, I wonder whether or not I can ...
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### Confused about the Mann-Whitney $U$ test. Does it test distribution equality (pdf) or just mean/median equality?

I am rather confused about the Mann Whitney test, many statements I read state it tests for distribution equality between two populations and some state it tests for means/median/central tendency only....
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### mannwhitneyu(x, y) or wilcoxon(x, avg(y))

Let's say I measure the happyness of my dog over 100 consecutive days. The happyness is measured continuously, and then averaged over 4 bins - (Morning, Afternoon, Evening, Night). This gives us a 2D ...
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### Comparing mean of multiple years data to a single year, vs. doing a regression

I am reviewing an article so I cannot give a lot of detail. But suppose you are comparing a number of measures (some quantitative, some dichotmous) over multiple years. The authors took the mean of ...
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### What is mean rank?

I am a student and I am doing a project that consists of calculating Mann Whitney U test. I would like to know the definition of mean rank that is calculated with this analysis. Also, I would like to ...
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### How to find which median is greater using Mann-Whitney U test or wilcox.test() in R?

I chose this non-parametric test because it is the alternative test to a 2-sampled t-test (Independent), since my data have a sample size below 30 and are not normally distributed. The Mann-Whitney ...
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### Large sample - statistical significance with minimal differences [duplicate]

Small disclosure I am doing a course that requires learning statistics but it is not my field of expertise so I may make several mistakes, apologies in advance. Also, I will add some background as ...
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### Are there standards for reporting non-parametric test results?

pretty basic question here. I'm pretty sure similar questions have been asked before (if you have any references that may help, you can send them too). Thanks in advance! I conducted some Wilcoxon ...
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### When is it correct to use a pairwise Wilcoxon rank sum test?

Following this answer, I was wondering when and why one should perform a pairwise Wilcoxon rank sum test, as exemplified by the R function ...
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### Wilcoxon-Rank-Test / Variance heterogeneity and skewed normal distribution / Power Simulation

I observe results that I cannot explain directly. I have created a simulation study where the data generating process follows a skewed normal distribution where the parameters of mean and variance are ...
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### 2D-KS test vs Mann–Whitney U test

Probably this is an easy thing, but I want to know what is the difference between 2D-KS test and Mann–Whitney U test and when to use which one? What I have understood that Mann–Whitney U test is a non-...
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### Alternative Effect Size for Mann-Whitney-U to Cliff's Delta

I am working with two variables that are not normally distributed with a large sample size in each group (n=287521, m=10863). After computing the U statistic and corresponding p-value, I tried to do ...
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### Classification using Mann Whitney U test

Can the results of a Mann Whitney U test be used to classify future measurements into one of the two populations? If not, is there a better way to convert the measurements of two populations into the ...
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### Mann-Whitney test for a large sample

I'm not a statistician, so pardon me for being naive on this subject. I'm trying to understand if there's any statistically significant difference in the medians of 2 groups. Here are some of the ...
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### For Mann Whitney U (Wilcoxon Ranked Sum), what is the difference between tests that follow the formula and use the smallest value?

I've learned two types of Mann Whitney U test, one use's a formula to calculate U, and another just takes the smallest total of the ranks and compares this with the critical value grid. What's the ...
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### Effect-size for Whitney-U-test for python

I have the following table as pandas dataframe with features feat1 and feat2: ...
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### Have I presented this Mann-Whitney U test appropriately?

I have collected data from two populations, M (males) and F (females) through a Likert scale of their agreement to a statement X The data is the following for females F And for M males As you can ...
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### could I combine t-test & Mann-Whitney U test and Spearman's & Pearson's correlation in one research?

I have two groups of participants (n=20 for each group), I would like to test whether there are group differences in cortical thickness (including multiple brain areas) and eye-movement performance(...
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### Wilcoxon (WMWU) test sensitivity

Statistics courses often give the Wilcoxon-Mann-Whitney U test ("Wilcoxon" from now on) as an alternative to the two-sample t-test. However, the test is not quite the test of medians that would be so ...
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### One-sample Wilcoxon test result does not make sense

To evaluate the correctness of a value I have given to something, I have asked a group of people to give a value for it. To evaluate the significance difference between my value with them, I am ...
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### Detect if there is actually two populations in a sample

I have been counting stomata on fossil leaf material to apply a known relationship between stomatal index and CO2. I thought that the material was all from one population (one species at a given site)....
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### Which statistical analysis should I perform if the data sets are not normally distributed?

I am doing an experiment where there are two independent groups; one is the group of "infected" patients another is the group of "sepsis" patients. I am comparing "platelet monocyte aggregates(PMA)" ...
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### How to explain to a non-statistician researcher why the 2-sample Hodges-Lehmann-estimator is reported instead of the difference in median?

I need to explain the result of the wilcox.test in R. Many people believe it's about medians. Of course it is not. I understand this is a useful non-parametric measure about statistical equality of ...