Questions tagged [wilcoxon-mann-whitney-test]

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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Appropriate test for two not-normally-distributed data samples

I have some data comparing training participants who experienced the same training course either face-to-face or virtually (via Zoom). I have two survey items I am comparing. Sample A is for virtual ...
32 views

Why are the stated facts about using the Mann-Whitney U test for post-hoc testing after a Kruskal-Wallis test a problem?

I've read here on several threads that using Mann-Whitney U for post-hoc tests are an issue because: the ranks that the pair-wise rank sum tests use are not the ranks used by the Kruskal-Wallis test (...
24 views

Mann Whitney U test criteria for the shape of the data

As far as I know if the assumption for Mann Whitney for similar distribution of shape is not met the test results represent the test of the mean rank instead of median. What does this mean for the ...
32 views

Actual difference between the statistic results from scipy.stats.ranksums and scipy.stats.mannwhitneyu

So, I have been trying to test if two independent samples come from the distribution, i.e. if they are greater or less than one another. Eventually I found out the Mann Whitney U Test is the ...
75 views

T-Test or Wilcoxon Rank Sum Test?

So, for an experiment I analyzed behavioral data of two different treatment groups with $n = 30$ for each of two groups, so 60 subjects in total. I used a computational model to analyze the data and ...
549 views

Can I use a Mann-Whitney U Test with a very small sample?

I want to compare differences between two independent groups (female and male) when dependent variables are continuous. However, my sample size is very small (N=6). I have done a Mann-Whitney U Test ...
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Concept Clarification: Wilcoxon rank test vs two-samples T-test (UPDATE)

I am currently deciding whether to use the Wilcoxon rank test vs two-samples T-test to assess BMI between two unrelated groups. Using the following code to assess normality ...
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Mann-Whitney with more than 10 repeated number of measures

I am currently assessing ab test result by using both bootstrap and u-test and both of them show different results. E.g. The effect on GMV could be significant by MW test but not significant in ...
13 views

Appropriate test to test for difference in mean (Likert scale)

I want to find out whether the mean of a certain variable (rating on a 5-point Likert scale) significantly differs from the midpoint of the scale, i.e. 3. My sample size is 48. I am wondering whether ...
63 views

Efficient calculation of critical values for Mann-Whitney-Wilcoxon

Most tables of critical values for the Mann-Whitney-Wilcoxon rank sum test statistic, usually known as U, are only calculated for very small samples. Presumably, this is because the test is most ...
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Using software to apply tests under different perspectives (sets of hypotheses $(H_0, H_1)$)

I have read very useful paper "Wilcoxon-Mann-Whitney or t-test? On assumptions for hypothesis tests and multiple interpretations of decision rules" by Fay and Proschan (2010). This paper ...
34 views

Wilcoxon Rank Sum Test appropriate?

I'm using Wilcoxon Rank Sum Test on my data and I'm wondering if there is a better alternative to use and eventually what post-hoc I could do on my data. Context: The objective is to find the ...
94 views

Assumptions of Mann-Whitney test for at least ordinal data

I am reading article by Divine et al. about using Mann-Whitney test for data that is at least ordinal (i.e. it may be discrete with many ties). It says the following (in section 2.3): That is, it (...
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How can we prove that kruskal wallis test and jonckheere test is equivalent to wilcoxon rank sum test?

How can we prove that kruskal-Wallis test and Jonckheere test is equivalent to Wilcoxon rank sum test when k = 2? And how can we prove that Friedman test and Page test is equivalent to sign test when ...
335 views

Should I make equally sized samples for the Mann-Whitney U test if originally I have unequal sample sizes

I have 2 groups with unequal sizes (control 70% and test 30%) and need to find out if there is a significant difference between these groups. I've read that MW test works fine with unequal sized ...
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Test which test to use: (Student-) T-test or (Mann-whitney) U-test

I've seen a couple of questions here around this alternative, but a -very basic- specific question I cannot answer from the top of my mind. Having a metric measure $M$ taken before treatize and after ...
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Method selection - multivariable non-parametric

I am not sure about the method selection for my data. Dependent variable: Continuous variable and grouped in ordered categories. As continuous it is not normally distributed but skewed to the right. ...
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Which is the most suitable non-parametric test (and post-hoc)for a heavily umbalanced groups (3, 15 and 11 observations)?

I am comparing soil properties among different geological substrates. I have only 3 observations in one category (karst soils), 15 observations in sedimentary terrains and 11 observations in ...
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Conflict between significance and importance. A paradox

When examining a set of proteins of healthy controls and patients I found significant differences using the Mann-Whitney test. However, when I used Random Forest, the most 'important' proteins for ...
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using Mann Whitney U test and t-test with multiple trials

I am testing some visualisations under two conditions and this is a between-subjects study, participants do two trials. Initially, I separated the trials and used a Mann Whitney U test to analyse my ...
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Why should I care about transforming the data for t test when I can use nonparametric Mann-Whitney-Wilcoxon test?

I ran into this question at my lab when I was trying to transform my data using things like log transformation, square root etc. when my lab members just directly asked me to apply mann whitney test ...
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Is Mann Whitney U the right statistical test for this analysis?

I am studying the spatial interactions between coral at a specific reef. I have the abundances of each coral species at each site we studied. I also have already run statistical tests and basically ...
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Wilcoxon signed-rank test vs Mann Whitney U Test [closed]

Background Qualitative measurements are taken of a subject before and after some external stimuli Aim Determine if measurements taken before and after stimuli are different (p<0.05) Question 1.) As ...
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Wilcoxon–Mann–Whitney test sample size

You serve two different versions of a website to customers, with the aim of seeing which, if either, is overall better. The two website versions are alternated by time of request arriving on the web ...
33 views

Is a Mann-Whitney U test appropriate here?

I need to run a stats analysis on data at the bottom of this post. Essentially, I want to investigate whether Diet Group (categorical independent var) or # of Stitches (categorical independent var) ...
59 views

Why does the Wilcoxon rank-sum care about data variance with uneven group sizes?

I was playing a bit with simulations to get a better of picture of how unpaired t-test and Welch t-test compare when comparing same-mean data with uneven variance. As a third test, I included the rank-...
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How to tune wilcox.test in R to compare means instead of medians

My question is: how does one tune wilcox.test in R to compare means instead of medians? Background According to this site by ...
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Permutation test vs Mann–Whitney U test

I am wondering if there exist any advantage of using the Mann-Whitney U test over a permutation test in the following setting: Suppose I have a group of animals with eggs in their brood chamber, from ...
300 views

What does comparing mean rank mean?

Lets assume that I am having 2 samples: Sample A 20 20 20 20 25 and Sample B 1 2 3 4 5 If I want to compare these two samples ...
135 views

How to correctly do a nested test (t-test, rank-sum, etc)

Let's say there are two groups of participants. Each group is randomly split into control subgroup A and task subgroup B. For each of the 4 cases some random variable $x$ is measured, whose mean is ...
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Statistical differences between proportion percentages of multiple groups

I have data about 3 categories of people and the frequency distribution percentages of how many times some people belonging to these categories have visited one of three restaurants over a certain ...
67 views

Asymptotic Distribution of AUC

It is well known that the area under the curve ($AUC$) is equal to the Mann-Whitney U statistic (c.f. Why is ROC AUC equivalent to the probability that two randomly-selected samples are correctly ...
24 views

Appropriate Mean Comparison Test for Grouped Data

I apologize if this is an elementary question. Let's say I have a dataset that has at least two dimensions. To fix idea, let's call it gender and country. Let's say there are two genders and four ...
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Pairwise comparison - too many groups

I have 23 groups that I am comparing. I was just going to show the distribution of the groups with boxplots but a reviewer of my manuscript wants me to do group testing. The trouble is that pairwise ...
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If I use the wilcox.test from R for paired data, what exactly it returns? I want to compute the effect size based on that

I want to calculate effect size for the paired Wilcoxon (signed rank). There are two options: Z/sqrt(N_pairs) or the rank-biserial correlation. The wilcox.test(... paired=TRUE) returns "V". ...
39 views

Mean of ratio, ratio of mean and statistic test

First off, I'm sorry if this has been answered or if the answer seem obvious, but I'm currently stuck and can't really wrap my head around the problem. So here are an example table of my situation (...
334 views

What can cause exploding statistic values and p-values near zero with the Wilcoxon-Mann-Whitney test?

I am using the Wilcoxon Rank-Sum/Mann-Whitney U test to compare metrics between two groups. In almost all cases, I get huge values for the statistic and only p-values around zero. In one case I got ...
31 views

Questions about derivation of Wilcoxon Signed Rank Test

I am learning some statistics on my own after my bachelor's degree. I am trying to understand the properties of the test statistics for the Wilcoxon Signed Rank Test (for paired data). ...
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Analysing before and after results of likert scale

I am a student with little knowledge on statistics. I ran a between subject experiment with 2 conditions, the control and test condition. In both situations I asked participants a set of 8 questions ...
86 views

Correct implementation of wilcoxon test for time series data in R

Am I testing the right thing or rather, am I testing what I think I am testing? As the answer of this question points out, a wilcoxon test is suitable to make statements about the inference of the ...
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How do I deal with ties when using rank-based normalizing transforms, e.g. Blom?

I would like to transform heavily skewed data with range (-Inf, Inf) and heavily zero-inflated into a form suitable for using GLMs for significance testing. Zero-inflation precludes the effective use ...
32 views

How to compare the distribution of partially paired ordinal data

I have multiple methods that are intended to measure the same ordinal quantity about a number of entities. For each of these methods, some of the values are missing and I know that this missingness is ...
42 views

Consistency of Wilcoxon rank sum statistic

In Chapter 1 of E. L. Lehmann's book Nonparametrics, he refers to the Wilcoxon Rank Sum test in treatment-control experiments. Using Lehmann's notation, let $N$ be the total number of units, $n$ the ...
41 views

quantile regression result different from Mann-Whitney U test

The results of the quantile regression and Mann-Whitney U test are very different. My sample size is 39. The quantile regression returns p-value of 0.83, while Mann-Whitney U test gives 0.33. Why are ...
39 views

Mann-Whitney U Test with SciPy

I would like to compare two datasets. Each dataset includes the ratio of chosen features (number of chosen tokens/number of all tokens in the document). The distribution is not normal. I want to check ...
95 views

Can the Kruskal–Wallis test be used to compare two time series?

I'm trying to compare two time series and determine whether they have similar distribution, trends, seasonality etc. So far, I've seen that Dynamic Time Warping and auto-correlation plots can be used ...
167 views

P-value correction for multiple comparisons using Mann–Whitney test (using R)

I have questions regarding the adjusted p-value for multiple comparison using Mann–Whitney test. The data structure that I am dealing with is something like this: Two groups to compare: Group 1 vs ...
115 views

P-value correction for multiple comparisons using Mann-Whitney test (using R)

I have one question regarding the adjusted p-value for multiple comparison using Mann-Whitney test. The data structure that I am dealing with is something like this: Two groups to compare: Group 1 vs ...