# Tagged Questions

The Mann-Whitney test is a non-parametric rank test to assess "whether one of two samples of independent observations tends to have larger values than the other" [Wikipedia].

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### Non parametric comparison: is Mann-Whitney Test applicable?

I think the Mann-Whitney Test is the right one to use for the following but I'm not confident. Could someone advise please? A footballing analogy for some real data: based on salaries we identified ...
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### How to test group differences when elements within a group are not independent?

I have 4 groups. Each group contains scores for items collected at different time stamps from a real-time system. Here is some dummy data: ...
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### Cupcakes! Which Test for multiple Paired Data?

I have a cupcake factory. There are an infinite number of cupcake machines. We also have 5 taste testers. These taste testers claim to be in complete agreement over how they rate cupcakes. They claim ...
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### What model contains Wilcoxon's rank sum test?

As Frank Harrel mentions in the answer to Logistic regression and Wilcoxon test, Wilcoxon's rank sum test (aka Mann-Whithey test) is contained in the proportional odds logistic regression, which would ...
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### Is there a nonparametric test available in R to test for a trend in a binary variable?

I have e.g. the following (n=14) time series data: 0,0,0,1,0,1,0,1,1,0,1,1,1,0 By looking at this time series, it is easy to see that in the first half we have more zeros than ones and in the second ...
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### Which nonparametric test should I use

I am currently doing an experiment to test whether there is a significant difference between test results of a control group of steel bars of good shape and another group of corroded steel bars. I do ...
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### If two groups are significant in a Mann-Whitney U test, should they also be significant in a Dunn's test?

I just ran across something that I thought was interesting but don't fully understand. I have some categorical data that I am comparing in R. I use a Mann-Whitney U test when there are just two groups ...
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### Testing for Stochastic Dominance - Mann Whitney with Unequal Variance

I've been looking for methods like Mann Whitney, but without homogeneity of variance. So far, I found that I suppose to test for stochastic dominance instead - i.e. modifying the null hypothesis. ...
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### Mann Whitney U test with normal distribution approximation: null hypothesis rejected?

I'm new with U test and I have some doubts about the rejection of the null hypothesis with the U test with normal distribution approximation. In my example I used this data for a 1 tailed test:  ...
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### How to generate t-test with data sets on different scales?

Let's say you repeat an experiment on two different days. On day 1 you get the following data: Day 1 ...
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### Significant two sided Wilcoxon rank sum test: Which group has higher median?

I conducted a Wilcoxon rank sum test with continuity correction, which produces W = 7195.5, p-value = 0.07094. This lets me confidently reject the null hypothesis of no true location shift at a ...
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### Excel Realstats MANN_EXACT function

I'm trying to compute some mann-whitney tests on my datas, and I use the really handy "Realstats". As you can see on this link, there are several functions available. As a noob in stats, I used the ...
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### Mann-Whitney output confusion

In an experiment I exposed each of 4 subject groups to a different condition to observe the impact on dependent variable. Assumptions for parametric tests were violated hence I decided to employ non-...
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### Why are these differences not significant (Mann-Whitney U test)?

For my academical research, I have generated eight Twitter bots. Each bot is specialized in one subject. I have four subjects and two genders (a bot can be either male or female), and each bot has a ...
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### Comparing capture rates in 2 groups: which test?

I am comparing rate of capture (animal captures per hour) between two years. I'm interested in determining whether there is a difference between rate of capture between the two years. A survey night ...
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### Different sample sizes, skewed data and unequal variances

I am a bit confused regarding best statistical test to use for my data. Here is the details: I did a study to compare two independent groups; 31 patients and 60 healthy controls. I have around 50 ...
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### Can I conclude whether these two populations are different?

I'm trying to determine whether my patient population differ from my control population in regards to number of children fathered per individual. The tables show the frequency of amount of children ...
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### With or without outlier and/or parametric vs non-paramteric

I'm comparing two group on the number or movie seen in the last mont (30 people in each group). Spss say that there 4 outlier but when I'm lookin with the z score I only find 1. If I do a t-test it'...
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### Mann-Whitney U suitable for my analysis procedure?

I examine the relation of written language of investors and investment performance of investors. N=52 Dep. variable -> investment success; binary (1/0) (Acquisition/no Acquisition) (N = 28/22) Ind....
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### Does Bonferroni apply to inference from parametric and non-parametric models?

I have run 6 independent-samples t-tests, and 4 Mann Whitney U tests. When applying Bonferroni correction, does it apply across all 10 tests? My hypotheses are that there will be 4 significant ...
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### determine which of the populations is “larger” with Wilcoxon/MannWhitney test

when using Wilcoxon test in Python - I get that one population is significantly different (greater) than the other. Where in the output do I get which population is actually the "larger" one? would ...
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### Is there any test, like Mann Whitney U test or Kruskal Wallis test, that allows me to include a categorical covariate (like an ANCOVA)?

Here is my question: I want to know if there is a test that allow me to do an nonparametric ANCOVA. Let me explain: I am looking for a Mann-Whitney-U and a Kruskal-Wallis, but I want to include a ...
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### Should I use Wilcoxon Signed Rank or Mann Whitney U in this question?

Stats newbie here currently trying to teach myself some stats topics. When testing for evidence that mean earnings per share were higher in 1988, should I use Wilcoxon Signed Rank since the samples ...
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### Compare two values for same measurement between two groups

I have a set of data, that I need to compare. Set consists of two measurements from same individual (right and left arm and legs for example)k like below: ' values_1right - 1, 4, 5, 7; values_1left ...
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### Is Mann Whitney U test appropriate for samples of really different sizes and distribution?

A Mann-Whitney U test on two samples of different sizes (Group A: 170,000) Vs. (Group B: 200), different distribution shape (as per Kolmogorov-Smirnov Tests ks.test ...
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### Most appropriate test for count data

So I've performed an experiment whereby I had 12 1km transects. 6 of these were along rivers running through agricultural land and 6 through woodland. These were arranged in pairs so that each agri ...
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### Paired or non-paired data? comparing two sets of scores from same individuals

I have data from four companies, W, X, Y and Z. For each company, three groups of 5 individuals (15 individuals total) take part in a test. Every individual takes two tests, test A and test B, with A ...
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### Relationship between AUC and U Mann-Whitney statistic

Recently I learned about the relationship between Area Under (ROC) Curve and $U$ statistic of the Wilcoxon-Mann-Whitney test. It is supposed to follow the following rule (got it from this nice post on ...
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### Mann-Whitney-U-Test as a replacement for Chow-Test?

The Chow-Test tests if there is a significant difference between a pair of regression equations under the null hypothesis the two models are equivalent. My idea is to use the Mann-Whitney-U-Test to ...
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### Change point detection test using Pettitt-Mann-Whitney test?

I am getting two change point with same p-value (or 90.27% probability) in an interval of two years i.e., 1955 and 1958. Here the trend is increasing from 1901-1955 and 1958-2015. How it could be ...
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### Mann-Whitney test W statistics

Below is Mann-Whitney test result from Minitab. At the end of result, there is no p-value but "Cannot reject since W is < 363.0". What does it mean? I cannot ...
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### Wilcoxon Rank-Sum vs Signed Rank for paired

I'm working with a dataset that contains paired samples (but some samples are missing their pair) and I want to check for an association between a binary variable and a bunch of numeric variables. ...
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### To use a two-sample t-test or to use a Mann-Whitney U-test on spatial data?

I have obtained some mean summer temperature records (June 1st- September 30th) for all years within the 1930s (1930-1939) and I have obtained summer temperature records for all years within the ...
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### Statistical tests for uneven groups

We performed an experiment (usability testing), which had two independent samples, one group with 5 participants and the other with 24. Based on the analysis of the distribution of the data (Shapiro-...
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### One-sample test, small sample size (n=3), non-normal data

I have approximately 5,000 variables, each with 3 data points. These numbers are ratios, i.e. bounded at 0 and generally non-normal. I'm interested in testing whether the mean of each of the 5,000 ...
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### Estimating sample size for Mann Whitney U test

I'm trying to estimate the required sample size for 80% power in an A/B testing, comparing user ratings with the Mann Whitney U test, and I'm having a problem with the power estimation. I'm using ...
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### Comparing two groups with multiple samples for each subject

Assume that you have multiple patients and control subjects. For each patient and control subject, you take two blood sample and count the number of bacteria you see in each sample. In the end, you ...
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### How to compute difference in location computed in Mann-Whitney-test?

I would like to reproduce the results of the Wilcoxon-Mann-Whitney-test in R wilcox.test(x,y,paired=FALSE, conf.int=TRUE. I succeed to get the W-value but didn't ...
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### Can the Mann-Whitney U test be used for related data?

I am comparing the annual profit margins of a set of 15 restaurants before and after they gained a "Michelin Star". I have multiple non-uniform numbers of profit margins for each restaurant before ...
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### Using Mann-Whitney U instead of T-test in large sample

For my dissertation, I am examining racial differences in perceived choice and control and home and community-based services (HCBS) use in frail elders (n=659) who have moved from a nursing home into ...
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### Non-normal, related but non-paired data, test for significant difference

i am comparing the profit margins for restaurants prior and post gaining a michelin star. I have all the profit margins for each restaurant up to 2-5 years prior and post. I want to compare all of ...
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### How do I get which experiment is doing better using the Mann-Whitney U Test?

The material I got only described how to test if there is difference (null hypothesis: H0 = H1). However, what I want to test is if the test version is doing better than control: null hypothesis: H0 ...
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### Is the Mann-Whitney U Test appropriate for assessing the busiest day of the week?

We have ten years of data where the average overall reveals that Monday is the busiest with the most visits to the hospital. We would like to provide a p-value to support that observation. Given ...
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### FDR correction of Mannâ€“Whitney U test

I have applied the limma moderated t-test on some proteomics data, on the label free quantitation values of proteins between control and exposed groups (2 samples each). Limma outputs p-values and the ...
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### Am I using the Mann-Whitney U test correctly?

I have two samples of online articles of different forms (one sample contains posts without infographics, and the other with infographics). Sample 1 (w/o infographics): n = 4993 Sample 2 (with ...
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### How is the Mann-Whitney U statistic calculated in SPSS?

I get different results using NPTESTS and NPAR TESTS in SPSS for the U-statistic. Can someone please tell me which formula is used for these two procedures, respectively. It looks like NPAR TESTS ...
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### Any alternatives to Kruskal-Wallis and post-hoc tests?

I have non-parametric data comparing people's sense of community scores who use different modes of transport to travel I want to see if there are significant differences between the three modes of ...
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### How to interpret Mann-Whitney's statistical significance if median is equal?

Testing the difference between the observations of two groups by using Mann-Whitney Test has given the following output (from minitab): ...