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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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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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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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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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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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Is this a good approach to check for batch effect?

I am not the best in maths, and slowly diving into statistical analysis. I know there is a lot of possibility to check batch effects, I just want a very simple way on my case. I have a dataframe of ...
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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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Perform Mann-Whitney U test after pairwise regression to characterise two groups

I have microarray data for infected and uninfected mice. I would like to calculate the distances in expression values within each group, and then use a Mann-Whitney U test to determine if infected:...
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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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29 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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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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Comparing groups? Wilcoxon, Paired test?

I am carrying out a simulation experiment where a fixed number of resources are, at the end of the simulation, divided between two groups of individuals, 'A' and 'B'. There may or may not be the same ...
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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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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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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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Which bivariate analysis to use for determining significance in predictors between two groups?

I'm conducting a "typical" statistical analysis in my research, but I have a few questions regarding appropriateness of the tests I'm using and whether or not I'm doing things the correct way. I don't ...
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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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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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Mann-Whitney-Wilcoxon-Test: should I transform my categorical data to have more realistic intervals?

I want to know whether old impaired people (75+) are more likely to use less the bus than younger impaired people. My respondents did not indicate the amount of days they travel by bus per year, but ...
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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 ...
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(Another) What Statistical Test Should I Use?

If I ask 600 different people to rate 3 different images from 0-10 (i.e 3 samples of 200 people per image) and I calculate the mean scores per image as well as the overall mean for all 3 images, can I ...
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multi-level Wilcoxon analysis

The question was originated from the paper [1] Table 3 [2], for every species, there was a data frame with two column: disease categories and the conservation index. Conservation index is numeric. The ...
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Analyzing impact of categorical independent variable on Likert Scale dependent variable

I'm working with customer satisfaction data on a 1-7 Likert scale with 7 being the "best". I have two distinct response groups, one of which participated in an additional experience and one that did ...
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Appropriately comparing subset to entire population

I am currently running a few analyses in which I want to compare a subset of my sample data to the entire dataset. More specific: I want to find out whether respondents who live in a certain ...
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1answer
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What is the approrpriate use of Continuity Correction when performing Mann-Whitney U analysis with small (n= 4) & discrete samples?

I am using Mann-Whitney U analysis (through R (whilst attempting to justify [STATISTICA] outputs). The data do not conform to a normal distribution, are discrete and are small in sample size (n = 4)....
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extreme right skewed data, bootstrap or mann-whitney?

I am an old dog (DB guy) trying to learn new tricks (stats) and was hoping someone here could tell me if this is a good approach: I have to analyse extremely right skewed counts of events over a ...
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1answer
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comparing the means of multiple distributions

I wish to compare the means of three independent data sets. These are exam scores that are from class A and class B and class C. Class A and B are normal and tested ok for homogeneity. A T-Test ...
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374 views

wilcox.test R question

I have a question about using wilcox.test in R. I have the following code/data: ...
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1answer
44 views

mann whitney assumption

By testing i found my data is non-normal so i can't apply t-test moving toward non-parametric test(mann whitney -U) the assumption that both distribution have same shape is violated although it is non ...
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1answer
65 views

Is dunn.test for two samples equivalent to wilcox.test?

I know that dunn.test is generally used as a post hoc after Kruskall Wallis to see which groups are different, but to generalize the function I am writing, I was wondering if when only using two ...
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2answers
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Is non-parametric test robust to Gaussian data?

1) Is non-parametric test robust to Gaussian data? For example in a case where the post-processed data is both Gaussian and non-Gaussian (eg RSME of multiple variables). I have growing concern if the ...
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1answer
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Independence test informs paired difference test in matched pre/post settings?

I have a, perhaps faulty, intuition that if a paired difference test (e.g., Wilcoxon rank sum, t-test) for a pre/post item looks significant, one should use caution in interpreting this fact if an ...
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Wilcoxon matched pairs signed rank test difference in medians but insignificant?

I am trying to understand the result of the Wilcoxon test I used on my small sample. For one measure there is a big difference in the medians between the two conditions. However, the result is highly ...
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1answer
92 views

Strange results when applying Wilcoxon test in R

I am interested in whether the mean of one sample is statistically greater than the mean of the other one. The samples are not independent in that if the ith observation in sample A is positive, than ...
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0answers
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Appropriate statistical tests to see effect of an intervention on binned or categorical data

I am looking at the effect of an educational intervention on a classroom by examining the change in the students letter grades. Dummy Example: Test Cohort (100 students) Letter grade for each ...
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1answer
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Understanding hypothesis testing (Kruskal Wallis, Mann-Whitney) when there are tied values

tldr: In Python's Scipy stats modules, the kruskal and mannwhitneyu functions will both raise an error if called with only ...
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Test if two distributions are same up to translation

The Mann-Whitney U Test can be used to test whether a randomly selected value from one distribution, $\ f_1(x)$, will be less than or greater than a randomly selected value from a second distribution, ...