All Questions
Tagged with nonparametric wilcoxon-mann-whitney-test
176
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Can I use Mann-Whitney U test for within group analysis?
I am conducting a within-group study where participants rate the perceived helpfulness of ideas on a Likert scale (DV) across two different days (Day 1 and Day 2), serving as the independent variable (...
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9
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Basic question regarding before and after intervention analysis on groups of different sample size
Apologies for the basic nature of this question. I have collected data before and after an intervention and assessed response to the intervention using a survey. This was a basic survey using a 1-5 ...
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2
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163
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Parametric vs Non-parametric test recommendation
What type of non-parametric test would be suitable for the dataset shown in the image:
The sample size is 200 each for both variables. The data value can vary from 0-4 for both variables. The ...
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votes
1
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538
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How to deal with negative values after subtracting the background?
I am working with Luminex data and have a question regarding the treatment of negative values after subtracting the background average. Specifically, I would like to know if these negative values need ...
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1
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210
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Kruskal-Wallis returns only one significant group (out of 4 groups), when significant group is removed and test redone, another group is significant?
I am comparing 4 groups of samples using SPSS. The groups are 4 bathymetry groups (>0m, >-1m, >-2m, >-3m). Within each group are a number of samples n. Each sample has a recorded seagrass ...
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97
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Is there an optimality result for the two-sample Wilcoxon-Mann-Whitney test?
Is there any mathematical result that states that the Wilcoxon-Mann-Whitney (WMW) test is optimal in some sense, for a specific testing problem that is a subproblem of the general problem the WMW test ...
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428
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How is the Mann Whitney U test statistic derived?
The t-test statistic is derived from the CLT and allows for some probabilistic statements to be made.
$$ U_1 = n_1(n_1+1)/2 + n_1 n_2 - R_1 .$$
I know the test does not assume a probability ...
- 741
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95
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Common language effect size / Probability of Superiority with Measurement Error
The setting is comparing two independent groups represented by random variables $X$, and $Y$. The common language effect size / probability of superiority / relative effect ... is defined as $p(X,Y)=P(...
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1
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689
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Small sample size: Permutation test or Wilcoxon test?
What do you think about using a permutation test each time the sample size is too small to meet the the assumptions of normality and homogeneity of variance etc ? Why do we use a non parametric ...
- 579
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1
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567
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Which non-parametric test should I use to compare 2 independent groups when i have several ties (Wilcoxon not good for this weird sample)?
I'm doing an analysis of a master's student in which I need to compare a continuous numerical variable between two groups. The samples are independent and each group contains only three observations ...
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134
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Alternative for Wilcoxon Test?
I'm ending my Master's Thesis, and I'm trying to figure out which test to use to calculate the significance of my data.
Basically, we measured the Free Kick biomechanical parameters of several ...
2
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1
answer
176
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Can the Mann-Whitney test be used to analyze two different Likert scale questions answered by the same users?
Can the Mann-Whitney test be used to analyze two different Likert scale questions answered by the same users before and after an experiment? For example, question 1 is asked before doing an experiment ...
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194
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How to conduct a boostrapped or a permutation wilcoxon test (in R)
I have a total of 18 mice, 9 from Healthy group and 9 from Sick group. Since I have a very poor sample size I would like to use boostrapping or permutation test.
Is there a way to conduct a ...
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1
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2k
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How to handle ties in pairwise wilcoxon rank-sum test?
I am willing run the wilcoxon rank sum test for different combination of variables, and using the base R code, I get a lot of warnings. The reason is that there are so many (about 30% of the whole ...
- 143
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239
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Wilcoxon Rank Sum test - appropriate to compare frequency of events between two sources?
I have some data on the frequency that a particular claim is referenced by two distinct types of sources. The first is traditional news media, and the second source are conspiracy theory sites. I want ...
- 323
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50
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How to validate the effect of the type of Task on participants' performance using count data
We conducted a user testing with two groups of participants (Group_A, Group_B).
Group_A performed Task_A (a writing) under Condition_A.
Group_B performed Task_B (a writing) under Condition_B.
Group_A ...
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2
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1
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33
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Compare whether one group are significantly closer to real observations than other
I have two groups consisting of non-parametric estimated data of a phenomenon. I want to compare these two groups of estimations with a third group of real observations of the same phenomena. ...
1
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1
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582
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Welch's t test vs Mann-Whitney for very unequal groups
I have two vastly unequal groups (n1=18 and n2=400), and want to test mean differences between the groups for some 700 parameters (more specifically, RNA expression levels for 700 genes).
While I ...
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3
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1
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198
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Multiplicity correction after performing non-parametric tests
This is a theoretical question.
I am wondering if multiplicity correction is applicable in the case of non-parametric tests.
I have performed some Mann-Whitney U rank test on two independent samples ...
- 120
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0
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489
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Wilcoxon test for independent groups, but with repeated measurements
I need to compare the average amount of money earned by the control group versus the experimental group on a trial level. Each group has 25 subjects.
The variable doesn't have a normal distribution, ...
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39
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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 ...
11
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3
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9k
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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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2
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337
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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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65
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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 ...
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119
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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 ...
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vote
1
answer
106
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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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2
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2
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132
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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 ...
3
votes
1
answer
982
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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 ...
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1
answer
138
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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 ...
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189
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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 ...
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2k
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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 ...
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1
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339
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Which form of stochastic dominance is tested for using the Mann-Whitney U hypothesis test?
The Mann–Whitney U test has the following interpretation reported on wikipedia:
[...] is a nonparametric test of the null hypothesis that, for randomly selected values X and Y from two populations, ...
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345
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Interpret Mann–Whitney U Test with highly skewed data
I have data for ~102,000 hands of bananas. The dataset has four data points:
Spiders present (True/False)
Count of rotten bananas in hand
Count of total bananas in hand
Percent of bananas that are ...
- 245
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0
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30
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Testing tuples of response variables
I'm struggling with comparing samples with multiple response variables, where such variables have a strict precedence or importance order. For the sake of this exercise, let's assume that each sample ...
- 121
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1
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1k
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One-sided or two-sided Wilcoxon rank-sum test depending on fold change
I am looking at fold changes $\frac{B}{A}$ over many different genes and I want to test with a Wilcoxon rank-sum test if the samples significantly differ.
I want to have as much power as possible ...
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2
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43
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Is there a way to quantify how appropriate a t-test is for given data?
I'm doing some programming and analysis for a post-doc who used to do this workflow using Excel and StatPlus. Apparently StatPlus has some feature where you tell it to compare two samples, and it will ...
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1
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298
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Step-by-step explanation of Likert scale/item statistical analysis?
I am looking for resources (books, online, articles) which have a step-by-step explanation of how to test hypothesis using Likert scale/item data. So far, I've learnt that non-parametric methods are ...
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1
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672
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Test the hypothesis that median is zero using Wilcoxon rank sum test
A random sample of seven boys was selected from a group of boys in a senior class who lived on
farms. Another random sample of nine boys was selected from a group of boys in the same class who
lived ...
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1
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1
answer
2k
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Use of Mann-Whitney w/ Ties
I am tracking the results of a test between a control group and 1 variant group. Each group contains (an unequal quantity of) users whose order count we're now tracking. The histogram is heavily ...
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1
answer
2k
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Permutation test and wilcoxon rank-sum test giving different results
I am comparing the revenue (at user level) between control & test to see if there is a significant difference. Both control & test have roughly about 39k data points . I am doing a permutation ...
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4
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1
answer
164
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T-Test or U-Test
I have a number of items that are based on a Likert scale, with values ranging from 1 = not at all to 5 = very much so. I would like to compare answers to these questions between two groups. I would ...
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0
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240
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Whitney Mann U test vs Kolmogorov Smirnov for a highly skewed continuous variable
I would like to compare task time to completion distributions (measured in minutes) across two groups. The distributions are highly skewed (the means are 300 to 400 times larger than the medians) and ...
- 143
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670
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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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724
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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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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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1
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77
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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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2
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2k
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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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5k
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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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178
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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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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)" ...
