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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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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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52 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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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
41 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
83 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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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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53 views

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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Rating Scale Data: MoE vs Chi-Square vs WMW Rank Sum Test

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
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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
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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
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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
86 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
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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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38 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 ...
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What type of test I shoud use between two samples to compare mean equal.? [closed]

I would do Wilcoxon rank sum test to compare mean equal. In R >wilcox.test(a, b) We can assume non-normality of the samples.
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Imposing orders on distributions based on Wilcoxon test

I am trying to figure out part of a text I am reading about non parametric tests. In there it is stated that: The fact that the output of a rank test is driven by the probability that a value ...
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Exact p-value calculation for Wilcoxon-Mann-Whitney U-Test in the presence of ties

Mann and Whitney's paper on the Wilcoxon-Mann-Whitney U-Test (https://projecteuclid.org/download/pdf_1/euclid.aoms/1177730491) shows how to calculate the p-value when the samples are small: an exact ...
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Is the R function wilcox.test only useful if samples have same variance?

I have two samples of observations drawn from distributions with different variances. To test whether they have the same mean, I plan to use the function wilcox.test...
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Is it okay to use non-parametric tests on normalized data?

I'm doing experiments with 3 conditions: A, B, and C. I have done the experiment 3 times, so each condition gets 3 values for a total of 9 values. Each value is actually an average of 5 measurements. ...
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1answer
47 views

multiple comparison with controls - kruskall wallis or mann whitney + bonferroni

I have a test group and two control groups. I would like to compare: test vs control group 1 test vs control group 2 and I don't need the result from control group 1 vs group 2. Therefore, in this ...
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Validity of t-test, Welch's t-test and Mann-Whitney U test

Suppose you wanted to compare whether the returns of stocks A and B had the same mean. It is unlikely they have the same variance. To do this you performed a t-test, Welch's t-test and Mann-Whitney U ...
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Prove the relation between two distribution functions

I have been given a homework in a subject called "Non-Parametric Statistics" and I'm a bit stuck with it. I would be very thankful if you could give me any advice or help, which would lead to a ...
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Example of an non-symmetrical Wilcoxon Rank Sum test statistic value

I have been given a homework in a subject called "Non-Parametric Statistics" and I'm a bit stuck with it. I would be very thankful if you could give me any advice or help, which would lead to a ...
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1answer
33 views

T-test or Mann-Whitney U test [duplicate]

Given the central limit theorem, can you always use a t-test to test a difference between two groups even if the data are not normally distributed but the sample size is large enough? Stated in ...
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33 views

Insignificant t test or MW U test yet high ROC AUC and vice versa

In SPSS, when I conduct a Student's t test or Mann-Whitney U test on (lots of) variables when comparing between 2 groups, some differences are denoted significant, and others aren't. When I conduct ...
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1answer
38 views

Is my model a good fit?

I am being tortured with the following problem... I have a set of crude mortality rates for ages 0 to 60. Let's call them Observed Rates. I use a smoothing technique (cubic spline regression) on the ...
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137 views

Wilcoxon rank sum test confidence interval by hand

I'm trying to find a 91.8% exact confidence interval for a sample with sizes $m=n=8$. I know wilcox.test gives the confidence interval but my instructor has told us to do it by hand. The formula for ...
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2answers
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Statistic of Wilcoxon-Mann-Whitney test with two-sided alternative hypothesis

I am learning about some non-parametric tests. In my textbook (the one that my teachers drafted), it is said that "The Wilcoxon,Mann-Whitney test does not allow testing the two-sided alternative ...
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1answer
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Which method should i use (comparison of two samples from UK general election with very different sizes)?

(edited version) I have a dataset of UK general election results and want to compare two groups on some criteria (education, health etc based on 2011 Census). These are the groups: the seats gained ...
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1answer
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Different p-value between KS test and Wilcoxon test

I would like to know if the values in vector A are greater than the values in vector B. Here are my two vectors: ...
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Statistical test for comparing the performance of two methods using absolute differences

I am doing a study where I have to compare tumor sizes measured using two different methods with the real tumor size. What I want to prove is that the absolute difference between method 1 and real ...