# 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.

884 questions
Filter by
Sorted by
Tagged with
1 vote
37 views

### Appropriate significance test for small sample size, unclear (non-normal) distribution

Given data: 30 datapoints in the form of usability scores (System Usability Scale) 2 groups within data (Group 1: 17, group 2: 13, independent, unequal sizes) Objective: See if there is any ...
• 113
27 views

### Seeking the Best Statistical Test to Establish Cutoff for Filtering False Positive Mutations in NGS Data

I have a program that calls mutations from patient DNA sequences. While the sensitivity of this test is 100%, it generates a large number of false positives (FP). I have developed a method to identify ...
161 views

### 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 ...
• 1,178
1 vote
30 views

### 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 ...
• 13
28 views

### 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 ...
43 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 ...
• 1,980
17 views

### 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 ...
• 13
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 ...
1 vote
40 views

### 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 ...
• 1,099
208 views

### 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: ...
• 19
143 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 ...
• 2,384
1 vote
65 views

### 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 ...
165 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 ...
• 593
33 views

### 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)....
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 ...
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 -> ...
• 101
1 vote
60 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 ...
44 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 ...
• 13
31 views

### 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 (...
• 1
50 views

### 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. ...
1 vote
55 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 ...
• 1,552
1 vote
90 views

### 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 ...
• 2,384
1 vote
75 views

### 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.,) ...
• 41
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 ...
• 21
48 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 ...
639 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 ...
• 2,384
1 vote
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 ...
• 137
370 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 ...
• 371
55 views

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 ...
759 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 ...
1 vote
77 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 ...
1 vote
119 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: ...
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 ...
1 vote
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, ...
• 41
63 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, ...
49 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 ...
• 3
36 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 ...
• 261
40 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 ...
• 101
442 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....
• 371
48 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&...
• 353
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 ...
206 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, (...
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. ...
1 vote
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 ...
65 views

### Best test to compare cell population counts across patient groups

Given a data frame structure similar to the following: ...
• 121
166 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 ...
71 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 ...
112 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 ...
66 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. ...
• 57
1 vote