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Questions tagged [wilcoxon-mann-whitney-test]

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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Is $F_X(t) > F_Y(t)$ a sufficient and necessary condition of $\mathbb{P}(X < Y) > 0.5$

I asked the question when conducting Mann–Whitney U test using the scipy implementation. The null hypothesis for one of the one-sided tests is $F_X(t) > F_Y(t)$, where $F$ denotes a CDF. I wonder ...
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Rank correlations: what is the difference between spearman coefficient and $R^2$? [closed]

When the data are not normal, how can the Spearman rank coefficient be interpreted differently from $R^2$? As I understand it, when performing a rank correlation, the axes typically shouldn't show the ...
Alpha's user avatar
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1 answer
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Best test for mortality rate in two countries

We’re trying to compare the mortality rate in two different countries over a period of 20 years. Is the Mann Whitney u test the best to use? We’re confused if the data is assumed to be normally ...
Jason Kimmings's user avatar
2 votes
0 answers
42 views

Unbiasedness Wilcoxon-Mann-Whitney Test

There are many different alternatives discussed for the Wilcoxon-Mann-Whitney test. One alternative is $P(X < Y) + \frac{1}{2}P(X = Y) \neq 0.5$. There are compelling arguments for this, such as ...
Julian Karch's user avatar
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Am I Doing Things Right? / negative binomial test

I have a dataset consisting of social media comments about a particular context from 1999 to 2024.The topic titles of the comments were annotated into two categorial variables = 0 and 1. I am aiming ...
berk's user avatar
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2 votes
1 answer
59 views

Mann-Whitney U Test for ranked data when there are only 4 ranks

During my university lecture I was told that for Mann-Whitney U Test on ranked data, the scale must have at least 5 different values (ranks). However, I am not able to find this information online so ...
pinkkdeerr's user avatar
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Can the One-Sided Mann-Whitney U Test Have a Composite Null Hypothesis?

Let's say there's an i.i.d. sample $X_1, X_2, \ldots, X_{n_1}$ from a distribution with the CDF $F$ and $Y_1, Y_2, \ldots, Y_n$ from a distribution whose CDF is $G$. As far as I know, the null ...
Milos's user avatar
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2 votes
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what is the meaning of “One-sample test.”?The following is clearly a two-sample test for wilcox.test

The code that inspired this question can be found here and below: ...
Apai's user avatar
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8 votes
1 answer
141 views

Is Kruskal-Wallis really a good test of stochastic superiority?

After much reading/googling, I reached the conclusion that the Kruskal-Wallis test (K-W) is a test of stochastic superiority (or, equivalently, of stochastic equivalence). Rejecting the null implies ...
jginestet's user avatar
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What does it mean for a variable to be statistically significant but not selected as important by classification methods?

I'm basically playing around with some lipidomics data to practice, so my question is purely theoretical. I wanted to see if I could find lipid classes that differ between two groups and I was ...
maglorismyspiritanimal's user avatar
4 votes
2 answers
162 views

Unexpected p-value distribution of Mann-Whitney U test under null hypothesis

I am getting very unexpected results of p-value distribution of Mann-Whitney U test under null hypothesis. I am working on a real data, but I was able to replicate the results on artificial data with ...
PtrZlnk's user avatar
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1 answer
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Appropriate test to prove hypothesis for given sample

Essentially, I'm writing a research paper, and I have these subjects grouped by their cancer stage from I to IV (ordinal scale) and whether or on they're positive for a specific marker (nominal scale)....
semperusfi's user avatar
0 votes
1 answer
25 views

How to compare semi-independent groups?

I need to compare the answers to a questionnaire (pre / post). The questionnaire was designed using a Likert scale. The two groups were made up of populations, some of whom were in both groups but ...
Heather's user avatar
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0 answers
48 views

comparing two matrices with wilcoxon test

I have two matrices A and B of 2388 rows and 1001 columns. I would compare two matrices with wilcox.test but is not clear to me if I had: directly input them -> ...
jonny jeep's user avatar
1 vote
0 answers
57 views

What is the correct way to perform one sample paired wilcoxon test?

for simplicity, let's say I have a dataframe called df, with two variables - weight_0 and weight_1. weight_0 describes the weight of participants before intervention, and weight_1 describes the weight ...
Luis_12345's user avatar
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43 views

Non-parametric statistical test to compare a continuous and dichotomous variable in the same group

I want to compare between the level of Th17 cells in the blood of a group patients with Sarcoidosis, and whether or not it is correlated with them having fibrosis. So, a continuous variable and a ...
Alpha's user avatar
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0 votes
1 answer
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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 (...
JBUG's user avatar
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1 answer
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ANOVA for a time-dependent data-set

my background is being an applied mathematician with some basic statistic background. I have a dataset containing a metric random variable whose value is to be explained by the categorical variable. ...
Michael Fischer's user avatar
1 vote
0 answers
54 views

What is the connection between permutation tests and rank tests?

I was trying to understand the null hypothesis of the Wilcoxon rank sum test and thought that the null distribution of the rank sum could be obtained by a permutation test/Monte Carlo test. If this ...
Ggjj11's user avatar
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1 vote
2 answers
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Mann-Whitney U test, compared to Binomial test

I was doing some simulations on the Mann-Whitney U test. I collected a number of U statistics (U is the smallest number of wins out of all pairwise contests between 2 samples: compare all values of ...
jginestet's user avatar
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1 vote
1 answer
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How is median of the difference calculated in Mann Whitney U test (TOST)?

I'm running wilcox_TOST in R and below is the result. If Mann Whitney U test is equal to Wilcoxon Rank Sum Test and considering what this test does (e.g., ranking the data and summing the ranks etc.,) ...
Lily's user avatar
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2 votes
2 answers
49 views

Subtracting the ideal-rank-mean in Wilcoxon rank-sum, what does it do

I am reading Discovering Statistics using R by Andy Field. In the section about how to calculate the rank statistic in MWU, one of the steps is to subtract the mean rank from the sum of ranks. W = sum ...
aflip's user avatar
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0 votes
1 answer
46 views

Best statistical method to compare model data with data from real measurements

I am relatively new to statistics therefore my question may be a bit silly, but I would like to compare data (soil water content) obtained from a mathematical model with data obtained from real ...
Skamby's user avatar
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11 votes
3 answers
623 views

Significant Mann Whitney, and significant t-test, but in the other direction

I was wondering if it is possible to have 2 samples (A and B), where A is stochastically dominant over B (via Mann Whitney, or Kruskal Wallis), but where conversely B has a significantly higher mean ...
jginestet's user avatar
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1 vote
1 answer
87 views

Proof of Probability of Obtaining U in Mann Whitney Test

I am trying to understand how the Probability Formula of U is calculated in this Paper, Equation 1 from section 4. Details: Suppose we have two groups A and B, each containing m and n samples ...
yo wa's user avatar
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4 votes
2 answers
362 views

Discrepancies between Mann-Whitney Test and Linear Mixed Model Results in R

I've conducted a four-phase experiment with physiological measures on two groups (Controls vs. Patients). After applying a Mann-Whitney test to examine differences between groups for each dependent ...
Ed9012's user avatar
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0 votes
1 answer
54 views

Statistical analysis of academic grades

Let's say I have 2 sets of grades from students. Maybe I'm looking at gender differences or some such but the disaggregating factor could be continuous or multinomial. Group A: 3 D's, 5 C's, 13 B's ...
Leonhard Euler's user avatar
4 votes
3 answers
758 views

Mann Whitney test problem

I have data from 4 populations : A (n=16), B (n=16), C (n=14) and D (n=16). Data from A and B are not normally distributed. Data from C and D are normally distributed. All data passed the Levene's ...
Steph Pauline's user avatar
1 vote
1 answer
76 views

Adaptive sample size for determining the significance of difference between two non-parametric distributions

I have two non-parametric distributions, A and B, and I would like to determine if they are significantly different (say, by the p-value of a U-test). Normally, I would sample $n=1000$ from ...
weidade3721's user avatar
1 vote
1 answer
114 views

Z score comparison in longitudinal studies

I have a longitudinal study with two time points (before/after), whereas a particular score was standardized across all individuals and time points, and thus provided only in terms of z-scores. (Edit: ...
Jonathan Bar's user avatar
0 votes
0 answers
9 views

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 ...
june2023's user avatar
1 vote
0 answers
55 views

Analysis of the difference between two groups on multiple outcomes

My question contains a few variations; I apologize for this in advance. I have two groups, and I have four outcome measures. These outcome measures are assessments of pain, function, depression level, ...
Ertan's user avatar
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0 votes
1 answer
59 views

One sided Wilcoxon test

I want to check whether a training program made an improvement on knowledge level on participants. I applied a test before and after the training to the same people (this means I have 2-samples, ...
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0 votes
0 answers
48 views

Hypothesis Testing - Varying p-value issue in my MWU

I have two machines (A & B) in our production line. A is older, B is very new. Both perform the same tasks, except that machine B is advanced and will perform 1 task less than the no of tasks in ...
AKK's user avatar
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0 votes
0 answers
33 views

Nonparametric test (akin to a sign test?) for multiple interacting effects across multiple conditions

Problem I have $K$ sets of conditions (index by $k\in\{1,..,K\}$), and each set has $N_k$ conditions. For example, if $K=2$ and $N_1=N_2=2$, we could call the conditions (A,B) and (C,D). I have ...
MRule's user avatar
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0 answers
39 views

Statistical significance test for average revenue

I have a dataset with a control group and a group who received a phone call. This is a subscription business, so the aim is to see if the average value of their subscription order increased. The ...
user13948's user avatar
  • 101
2 votes
2 answers
412 views

p-value correction after wilcoxon/mann-whitney test

I have a set of 56 variables, which are functional connectivity values, for two groups (control_group vs. patient_group) between two phases (pre-phase vs. post-phase). I have a small sample size (9 vs....
Ed9012's user avatar
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2 votes
1 answer
47 views

rank-sum test vs. anova

I have a set of data looks like this: hwid freq code output 101 5150 764 24 101 5170 768 24 101 5190 764 24 102 5150 752 24 102 5170 760 24 ... ... ... 24 The data represents "power level&...
xrfang's user avatar
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2 votes
0 answers
44 views

How to know if I have enough sample for a small sample t-test to be appropriate?

Say I have 15 or 20 samples each from two samples. The data shows evidence of strong skew. I am considering a two-sample t-test of means, based on the assumption that the sampling distribution of the ...
Estimate the estimators's user avatar
0 votes
1 answer
191 views

How to combine results from Wilcoxon Rank Sum Test for multiple imputed data sets from proc MI in SAS

Endpoint information: We have seizure count collected for every day and therefore there will be some missing for some days. We got average seizure frequency per 28-day, for an interval. That is, (...
Janet Xu's user avatar
0 votes
1 answer
38 views

Do I need to use a factor for the ANOVA? [closed]

The problem: A psychologist is interested in short-term working memory under (1) sleep deprivation, (2) a strong dose of caffeine, (3) following 8 hours sleep. They conduct a between subjects design. ...
Cathrine's user avatar
1 vote
0 answers
33 views

Which statistical test is suitable to compare order statistics of two independent samples?

Say I want to compare two order statistics (say the 2nd largest value or min value) of two samples. Let's not make any distributional assumptions except that the variance is finite? Is something like ...
Estimate the estimators's user avatar
2 votes
1 answer
65 views

Best test to compare cell population counts across patient groups

Given a data frame structure similar to the following: ...
DaniCee's user avatar
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1 vote
2 answers
163 views

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 ...
scouse_s's user avatar
0 votes
0 answers
67 views

Mann-Whitney-Wilcoxon test vs ANOVA for comparison of variable across multiple groups

When comparing a non-normally distributed variable across multiple groups, is it okay to use a Mann-Whitney-Wilcoxon test or is it necessary to use (non-parametric) ANOVA? The ...
NicolasBourbaki's user avatar
0 votes
0 answers
111 views

Correcting p-values when accounting for age and sex in a study where the main objective is to find differences between disease/control

So I analyzed my metabolomics data using Mann Whitney U tests and OPLS-DA. My data is super small, with the control group only having 5 samples and the other groups having 10 and 14 samples ...
maglorismyspiritanimal's user avatar
0 votes
1 answer
65 views

Mann-Whitney U Test - Interpretation

I have conducted a survey and would like to assess whether men compared to women differ in their attitudes. At a glance, the means differ quite much, which is why I wanted to prove it statistically. ...
ber1495's user avatar
  • 57
1 vote
1 answer
116 views

How to report a difference in means - Demographics

First of all sorry for the question, I'm having a hard time with statistics :) I have conducted a survey for my thesis and am currently analyzing and reporting the results. At the end of my survey, I ...
ber1495's user avatar
  • 57
4 votes
1 answer
99 views

Statistical test for nominal data, multiple variables and within-subject design in R

I have run a study comparing if a cheap ultrasound device (T) is as efficient at determining osteophytes as an expensive device (V). There was four examiners who reviewed each participant (ID) and ...
Kate Atkinson's user avatar
2 votes
1 answer
101 views

Best method to compare measurement techniques

I am wishing to test the equivalence, or not of two measurement methods. Some background, we have two test instruments (old and new) that measure radiation dose distributions compared to what was ...
James's user avatar
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