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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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Go with t-test or Mann-Whitney U test?

I'm measuring performance of 2 methods (method_A and method_B) that try to satisfy customers demands. Both methods produce ...
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Can I use the Mann-Whitney U test for this specific case?

I have a sample consisting of 750 Private Equity transactions where I got data on multiple variables such as return, size of investment, holding period and so on.. I am researching if two different ...
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When to use chi squared, kruskal-wallis and mann whitney u tests for statistical analysis? [closed]

We are currently conducting a study on the public perceptions regarding data collection for mental health smartphone applications. We have collected data through survey questionnaires and are trying ...
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Wilcoxon signed rank test - interpretation

I have 6 dependent variables that were measured on a 5 point Likert scale (treated as interval here). I want to test if their means differ significantly from the midpoint 3. As the normality ...
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Using wilcox.test() and t.test() in R yielding different p-values

This is a repost from the R forum, as I was told to post here instead. I would like to test whether there's a significant difference in the mean between this two samples: ...
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compute AUC and statistical testing of stratified data

I have a dataset where samples are stratified in groups. That is, there are N samples per examination, and M examinations per subject. I would like to account for this when estimating the ...
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What is the difference between “paired” and “unpaired” versions in Wilcoxon's test?

Statistical tests can e.g. be used to decide whether to accept, reject or fail to reject the null hypothesis (the status quo). There are (apparently) two variants of this Wilcoxon's test: paired and ...
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What does p-value of Mann Whitneyu t-test equal to 0 mean?

I'm trying to perform Mann Whitneyu test on a dataset. As the code is shown below, the data is grouped by different Medal value. Why the result p-value is 0? ...
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32 views

Mann-Whitney-U for exponential distributions?

I have two distributions, that look like the following: They appear to be exponential and have different sample sizes (369 vs 60). I would like to do some hypothesis testing. I know that I can use ...
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Data in the Mann-Whitney test

I have a simple question. I wanted to compare two independent survival curves, for example Online resources tell me that the Mann-Whitney test can be used to test two independent groups or ordinal ...
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What is the interpretation of the p-value of 2.2e-16? [duplicate]

I am a beginner in using Wilcoxon test to get the p-value. After applying the test to my data, I got the p-value < 2.2e-16. Does that mean that the samples I have are significantly different from ...
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An issue with computing the Wilcoxon test using R

I have two independet groups with many sub-groups (illustrated in the code below). I would like to calculate the Wilcoxon test for the two groups. To do that, I have written the following script in R: ...
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Comparing ways to create a composite score

Objective: I have biomarkers $X_1,\ldots,X_p$ (all in continuous scale) and a binary dependent variable $Y$. Because $p$ is large (there are many biomarkers), I want to make a composite score ...
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Mann-Whitney (2 groups) contradicted by Kruskal-Wallis (3 groups)

We have two groups that are significantly different (tested with Mann-Whitney). When a third group is added, the Kruskal-Wallis tests provides a non-significant result. This implies that two or more ...
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Wilcoxon Test gives W=0

I am running the Wilcoxon Test on my data, however, I get a W value =0. My questions are two: 1): Why is the case such a test gives 0? ii): How to interpret such results?
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Wilcoxon - one sample abnormal stock returns

I got a dataset with abnormal stock returns for around 400 securities and i need to find out if they're statistically different from zero. They don't follow a normal distribution, so i would like to ...
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1answer
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I need to use a Wilcox Sign Rank test with unequal sample sizes

I'm analyzing a before and after treatment of farm fields based on runoff from rainfall events. Over 6 different farm fields there were 136 water samples from before the treatment was installed and ...
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Multiple comparisons, should I run a one-way multivariate analysis or can I use Mann Whitney?

I am analysing some study data and am unsure the appropriate statistical test to use. The study involves watching a film. 50% of participants saw version 1, 50% saw version 2 - (the difference in ...
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Which statistical analysis to use on ordinal questionnaire data?

I would like to analyze data on questionnaire scores on quality of life between two different groups. There are 20 quality of life questions, all with responses on a Likert scale 1-7. So I have an ...
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Analyse continuous variable between two groups/arms: cluster randomized study

I'm analysing the data for a cluster randomized study. There are 66 clusters randomly divided into two study arms: control and intervention, 33 clusters each. In total there are 2098 patients. The ...
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Guidelines for interpreting Success Rate Difference from a Mann-Whitney U test

A reviewer recently asked me to perform a Mann-Whitney U test on some grouped data and to obtain a Success Rate Difference (SRD) as a measure of the size of the effect. This is the output of the Mann ...
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Is it correct that JMP has Mann-Whitney U for comparing more than 2 unpaired groups (instead of Kruskal-Wallis)?

To the best of my knowledge, the Mann-Whitney U test (also called Wilcoxon-Mann-Whitney) is for comparing only two unpaired groups, while the Kruskal-Wallis test is used for comparing two or more ...
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Compare categorical variables that are not(?) independent

I have some survey data in which respondents were classified in to two overlapping groups (i.e. respondents who work in a profession and people who do this same work on their own-- many people do ...
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Whitney-Mann and multiple regression

Is it appropriate to use Whitney-Mann (to compare the groups) and multiple Regression model (to analyse each factor) within the same data? (parametric and non-parametric test on the same data)
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Theoretically is it better to sample with or without replacement to approximate a rank test?

Let's say we want to do a rank test since we do not know the exact distribution. Say we have 3 different sample sizes. Which of the following tests (exact permutation, sample with replacement, sample ...
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Why is the AUC when plotted against the wilcoxon rank sum p-value, result in a plot that is not linear?

I have a binary response variable with many continuous predictor variables (about 5000). I first computed the AUC for each predictor variable, then computed the p-value associated with the AUC using ...
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How to take into consideration errors in Mann-Whitney test?

I have 2 independent samples (groups), each group contains 10 experimental values of variable T and their standard deviations (errors). I need to do intergroup statistical analysis, i.e. to elucidate ...
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212 views

t-Test with small sample sizes (10)

I am looking to compare the means of two sample populations of size 10. Ideally I would like to use an independent t-Test however I am concerned that the sample size is too small, as I don't know for ...
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2answers
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Appropriate statistical test for data which do not have normally distribution and do not have equal variance

My data has 150 samples and is not normally distributed, and it does not have equal variances either. I know t-test (e.g. this python method) can be used when data is normally distributed and it can ...
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Wilcoxon Test with Random Effect

I would like to test if there is a significant difference in the speed of movement between 2 treatments for different females. For each female, I have several sampling points. I have a table with the ...
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1answer
67 views

Mann-Whitney test interpretation

I would be grateful for any help. I am using a Mann Whitney test to determine whether there are differences between two groups (adopters and non-adopters) on 15 explanatory variables that are scaled ...
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1answer
385 views

Calculating degrees of freedom in a Mann Whitney U

I have completed a series of Mann Whitney U tests in R, and am looking for the degrees freedom. I'm comparing two datasets of n1=29 and n2=5, with StandardDev1 0.4525 and StandardDev2 0.3652. What ...
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Algebraic Manipulations in Mann-Whitney-Wilcoxon Test Statistics

Given Let $\Delta > 0 $ be positive real number. Consider the Wilcoxon-Mann-Whitney upper tail test $H_0: \Delta \leq 0 \,\,\, \text{vs} \,\,\, H_a: \Delta > 0$ aimed at testing the difference ...
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Test on Ordinal data with interval

I have a query regarding statistical analysis. I have collected data on percentage of savings done by individuals. These data are ordinal, grouped into equal intervals with the exception of the final ...
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Comparing 3 groups at 2 time periods

I'm analysing a dataset and comparing three zones at two points in time. The data in question is: Hourly sightings of wild fish (CPUE) In one of three adjacent zones (A, B, and C) During the ...
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1answer
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Mann-Whitney U test or Kruskal Wallis test for comparing median of two groups?

I know that Kruskal Wallis test can be used to compare median of two or more groups (e.g. see this link: https://www.statisticshowto.datasciencecentral.com/kruskal-wallis/ ), and that Mann-Whitney U ...
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Comparing changes in pre-post count results for two cohorts

Thanks in advance! I have a pre-post analysis Of cases and controls. The outcome variables of interest are emergency room visits and hospitalization visits - both rare occurrences with median = 0 ...
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Standard deviation in a non normal distribution

I have two datasets, dataset A with 5-10 values and dataset B with around 20 values. Both are non normally distributed and right skewed. Can I use standard deviation to compare the elements ...
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Appropriateness of running a rank sum test on Likelihood to Recommend data

I am working with Likelihood to Recommend metric that's measured on a scale of 1-10. The objective is to test for statistically significant improvement/decline (period over period) in the metric. On a ...
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1answer
61 views

How to use bootstrapping to compare two non-normal datasets

I have two data sets - one control and one treatment. I wish to test whether the difference between their means is significant or not (approx 30 data values in each set). The distributions of both of ...
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1answer
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Wilcoxon signed-rank test or One Sample t-test?

I conducted a training session and for each of my users, I measured pre and post score (before and after training session). Each of my users (n=28) is measured twice, so my data is paired: Data: <...
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1answer
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Derivation of the Mann Whitney U normal approximation

The normal approximations for the Mann Whitney U statistic are given by wikipedia but there are no refrences mentioned. What are the actual derivation steps of the untied and tied case approximations? ...
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non-parametric tests for repeated observations

I am looking for an RM-ANOVA alternative that fits with non-normal data that may not satisfy sphericity assumption. My dataset: Through a mark and recapture study, I trapped turtles, and collected ...
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Testing Evolutionary Algorithm output with Mann-Whitney Wilcoxon Test

I have designed a hybrid Evolutionary Algorithm for my research using Genetic Algorithms. Genetic Algorithms have different operators such as Selection, Crossover and Mutation. These operates are ...
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1answer
55 views

Wilcoxon Test - non normality, non equal variances, sample size not the same

I know there are already a lot of posts out there, but I couldn't find this exact combination in any of them. Comparing two samples (Prices associated with men and with women), but I have neither the ...
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1answer
33 views

Test to compare on an ordinal scale, two groups of data that have covariates

I have two (Test and Control) groups of data. Data in each group is divided into 10 (ordinal) period. In each of these periods, number of observation ranges anywhere from 22-53. The assumption is that ...
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1answer
126 views

Interpretation of Wilcoxon Rank Sum test results

I compared the two distributions shown below using a Wilcoxon Rank Sum test (two-sided) using R. The p-value of the test was highly significant (as shown on the plot) and is based on 1,320 ...
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1answer
44 views

Comparing two discrete independent variables

I would like to perform something like two-sample Wilcoxon tests/T-test (paired = FALSE) to compare two method's expected scores. Here is the table of counts: ...
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43 views

Compare Two Means Without Underlying Observations in R?

I have limited information with which to compare two means, is it still possible in R? We have a group of students (1,000 students) about whom we have mean and standard deviation information, and we ...
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t test on original result, log2(result), fold change and log2(fold change)

I have some confusion about t test on original result, log2(result), fold change and log2(fold change). Hope to get some expert opinion on this. Our original results are, for example, some biomarker ...