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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Interpretation of the test statistics of ks.test, ad.test, and wilcox.test
I am currently writing my Master's Thesis and I have a question in regards to the Kolmogorov-Smirnov test (ks.test in R), Anderson-Darling test (ad.test in R), and Wilcox/Mann-Whitney U test (wilcox....
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Repeated Measures Design: Wilcoxon Mann Whitney and Random Effects
I recently ran a laboratory experiment in which I clustered subjects by treatment each session (that is, in each session subjects were all in the same treatment; 6 sessions total). In my experiment ...
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1answer
41 views
help interpreting t-test and p-value - or help me finding a good statistical test
I have two samples
background
and
input
these are the histograms:
sample sizes are well above the 1000s, so the sample variance of the mean is pretty much low.
I'm trying to have a statistic ...
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1answer
15 views
Pair-wise Mann-Whitney U vs. ANOVA
I'm having trouble interpreting the results of comparing 4 sequences. All are fairly similar (in terms of mean) and I want to figure out if one can say that they that their difference in mean is ...
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1answer
19 views
Significant difference between two non normal and inhomogene groups
I've done some measurement of tissue rigidity. So I did 1.000 measures with healthy (n=300) and ill (n=700) people.
Now I want to find out if there is a significant different value of the measured ...
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22 views
This is a comparison between non-normal samples of different sizes?
I have 16 types of experiments (a matrix of 4 conditions and 4 bacterial strains).
Each experiment type is composed by a variable number of samples (4-8).
Each sample is made of a variable number of ...
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23 views
What tests are most useful for comparing two dependent samples of different size?
I have two samples of student data from within a computer lab environment and outside of a lab environment. The students (N=128) are the same in both environments, but I have a lot more data for each ...
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20 views
Wilcoxon rank sum test with a dichotomous dependent variable
I test the differences in medians for multiple variables of two (independent) samples using the Wilcoxon rank sum test; in some cases the dependent variable is also a dummy variable - I still obtain ...
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21 views
power of mann-whitney test
I've written in last post about two groups of data (case-disease) that need to be compare. This time I don't have binary data but variable data. Example below:
...
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23 views
Which Two-Sample Test for Non-Independent Data?
I am interested in determining whether there are statistically significant differences in the mean twelve-month (percentage) changes of various financial variables, conditioned on the state of the ...
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0answers
23 views
Interpreting Wilcoxon rank sum test/ have I used appropriate test for my data?
I am looking for significant differences in 6 factors between 12 different groups (6 separate tests), I have used the Kruskal- Wallis test for each comparison because my data did not meet the ...
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1answer
135 views
Performance of the Wilcoxon-Mann-Whitney test with large sample sizes (> 100,000) from medical data warehouses
Two large data sets of patients (set A: n = 100,000; set B: n = 700,000) are being compared with respect to their hospital length-of-stay (LOS). The variable LOS is reported as an integer in the data ...
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14 views
Comparing two independent distributions: statistical and practical significance
I am comparing two categories, X and Y, of data. The data for X and Y comprises social media posts and the corresponding engagement metric for each one. I have collected around 100 posts for X and 150 ...
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28 views
Hodges-Lehmann estimator as a percentage?
I'm comparing samples X and Y (of sizes M and N respectively). I need to report whether the samples are statistically different (Mann-Whitney U-test) and by how much (Hodges-Lehmann estimator) to ...
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1answer
69 views
Problem with Mann-Whitney U-test for large samples [duplicate]
I am comparing two categories (A and B) of social media posts with the corresponding number of likes for each one. I am taking samples of equal size from each category at random and performing a Mann-...
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19 views
Evaluation of difference and relation between two variables
I have got 90 samples for two variables A and B (it is 90 rows and 2 columns). A and B have integer values of 0, 1, 2 or 3.
First, I want to show that samples values in B are smaller than A in ...
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14 views
What statistical test for an A/B split using revenue and impressions? (Continuous Vars.)
I want to conduct an A/B test between two different Ad Copies I have for a given advertisement on Google.
Ad Copy A might have 30 k impressions (number of times ad was displayed) with approximately $...
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2answers
80 views
Interpretation of p-value in Mann-Whitney rank test
I am testing Mann-Whitney rank test with two vectors a and b. Vectors are almost similar so I expect a p-value near 0, but the ...
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Combining paired and unpaired samples in Wilcoxon/MWU test
I am trying to compare numbers in two sets (X and Y) to test if numbers in one of the set are statistically larger than the others. However, some of the numbers are paired, and some are not. For ...
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12 views
Testing for significant differences in Likert-type data, including random factors
I have data from a number of subjects who rated conditions 1 through 8 on a Likert-type ordinal scale (from “much worse” to “much better”, here, coded from -3 to 3). It results in the following counts ...
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1answer
68 views
Effect size and standard error for Mann-Whitney U statistic
I'm conducting a meta-analysis and one of the studies only reports Mann-Whitney $U$ statistic. The table with results is pasted below.
Circled in red is the $U$ statistic that tests the differences ...
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24 views
Compare center of two distributions
I have six vectors, each of length say $n$ which is >= 100. The vector entries correspond to a measurement from a certain experiment on $n$ individuals. Each index in the vectors corresponds to one of ...
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1answer
160 views
Best type of graph to represent data tested with the Mann-Whitney U-test
I am using a Mann-Whitney U test to compare the willingness between subjects to once monthly injection between two groups. One group is a control while the other is the intervention. I am expanding on ...
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4answers
101 views
Mann-Whitney U for two distributions with equal mean
I am doing a Mann-Whitney U test for two samples with the following descriptives:
...
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0answers
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Is there a Welch-like correction for the standard deviation of Mann-Whitney U or Wilcoxon W? [duplicate]
The Mann-Whitney U test or the Wilcoxon Rank Sum test is sensitive to unequal variances. Is there an equation that adjusts the standard deviation of this statistic, much like in the Welch-corrected t-...
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1answer
54 views
Mann-Whitney U Statistic seems very large - is something wrong?
I compared two unequal sized samples, N1 = 230 and N2 = 120 using a Mann-Whitney U test. The U is shown to be large such as 2829.
The p value is non-significant but I want to know if such large ...
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31 views
Mann-Whitney or K-W?
I am studying a biomarker in cancer, and I want to know if there are differences related with the location of the cancer (head and neck, lung or cervix).
When I do the Kruskall-Wallis test, I find a ...
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2answers
77 views
What test should I use for two groups of different number of measurements and low number of samples?
I have data that include 20 samples divided into 2 groups (category A and category B). The groups are independent, none of the value in one group repeat in other. N(A) =14, N(B) = 6.
here is the ...
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2answers
77 views
Wilcoxon-Mann-Whitney test giving surprising results
I'm comparing two datasets and want to test the null hypothesis on them. Both datasets contain a lot of meaningful zeros (around 50% of the values are 0). One of them, "test", has more zeros than the ...
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1answer
106 views
Mann-Whitney U test for sample sizes 65 and 10 in Python
I would like to run the Mann-Whitney U for two groups with sizes 65 and 10, where I essentially want to compare scores on some measure between two different groups.
I have two questions regarding the ...
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39 views
Should I do correction for multiple comparison in this case?
I am very confused regarding the correction for multiple comparison case, so I hope somebody here could enlighten me.
1) First question:
Say I have two groups; ...
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2answers
288 views
How can a Mann-Whitney U-Test return a p = 1.00 for unequal means?
I'm wanting to compare scores derived from a reaction time task between two groups with unequal sizes (G1 = 78; G2 = 23). However, when I run the U test it tells me there is no significant difference, ...
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1answer
84 views
How to compare diet composition
Problem description:
I have 14 faecal pellets from 6 bat individuals (3 females, 3 males). All pellets are approximately of equal size. Prey composition (3 types: A, B, C) has been determined by ...
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1answer
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Are my assumptions right for this question?
I answered these homework questions but I was told that at least one of my answers is wrong. However, I can't tell which one I answered wrong. What incorrect assumptions have I made?
QUESTION:
MY ...
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How do I test if distributions are similarily shaped in SAS?
I'm writing a group assignment in statistics mostly by myself.
We're trying to determine whether or not previous studies in mathmatics are correlated with better test scores in statistics (pass vs. ...
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Mann-Whitney U-Test — Names and origin [duplicate]
I have a rather historical questions that I have to ask here as I was not able to find an answer online or in most practical statistics books.
The Mann-Whitney U-Test is also called the Wilcoxon rank ...
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1answer
49 views
Mann Whitney test [closed]
I have data of 2 groups: 150 vs 70. Can I perform Mann Whitney test as my data was not normally distributed. Should the sample size of two groups be the same in order to run Mann Whitney test ?
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1answer
29 views
Distribution comparison for two highly size-different samples
I have the data for an ambulatory assessment for autonomic cardiovascular functioning and the labels for posture are really mixed (the number in parenthesis represents the code, not the number of ...
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1answer
17 views
Why the order of application of properties of Wilcoxon Rank-Sum makes a difference
Suppose I am calculating the p-value of a Wilcoxon Rank-Sum test where $W_s = 23$, $n=4$ and $m=5$ suppose that we have:
$pvalue = P(W_s \ge 23 | H_0)$
The way I manage to get to the right answer ...
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1answer
166 views
Mann-Whitney U Test Definition of U
What does U stand for in Mann-Whitney U Test? I can't seem to find the definition of "U" in any site.
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1answer
424 views
Wilcoxon Rank Sum (Mann Whitney) test-SAS Results Interpretation
I need a clarification on interpreting Wilcoxon Rank Sum (Mann Whitney) test results using SAS. Here is a sample results look like. I am trying to form a hypothesis and interpret the results. In this ...
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1answer
124 views
The most conventional way to report the difference between two samples (different size, varying distribution and skewness)
To begin with, I must admit, I am completely new to statistics. There are many discussions on CrossValidated on the optimal ways to compare the central tendency of two independent populations, which ...
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0answers
20 views
Nonparametric test for difference in trends?
I have an experiment where two groups of individuals get some variable repeatedly measured at regular intervals. I'd like to know if one group is trending faster or slower than the other (and in what ...
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1answer
274 views
When should I use `scipy.stats.wilcoxon` instead of `scipy.stats.ranksums`? [duplicate]
I've been using http://docs.scipy.org/doc/scipy/reference/generated/scipy.stats.wilcoxon.html but then I realized that there is http://docs.scipy.org/doc/scipy/reference/generated/scipy.stats.ranksums....
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1answer
113 views
Difference between wilcox.test using COMMA vs TILDE SIGN (and the interpretation of the resulting W-statistic)
What is the practical difference between wilcox.test(x,y, paired=F) and wilcox.test(x~y, paired=F) (i.e. using comma vs. tilde ...
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1answer
145 views
Clarification on Mann-Whitney-Wilcoxon Test
I was looking to get some advice on some analysis using R, I want to ensure I am doing everything correctly.
I want to compare test scores between two groups (A and B), I have two tests but wish to ...
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1answer
107 views
Where does the number 12 come from and why is it the same 12 in Wilcoxon and Kruskal Wallis?
I see that it has something to do with the variance and one has 12 on the numerator and the other denominator, but why is this the same 12 and how do they become inverse?
Equations:
Kruskal Wallis:...
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1answer
27 views
Comparisons on nonparametic, unequal variance data
I am trying to compare financial investment of 2 groups, however, my data is not normally distributed AND has unequal variance between the two groups. I thought of using the Mann-Whitney on SPSS but I ...
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111 views
Explanation of derivation(The Mann-Whitney statistic)
Suppose that the X’s are a sample from F and the Y ’s a sample from G, and
consider estimating, as a measure of the effect of the treatment,$$π = P(X < Y )$$
where X and Y are independently ...
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31 views
Tests of Association When Using Likert-style Ordinal Data
I am currently working with some survey data that has ordinal categories for drinking/substance abuse problem (0=Never binge drink, 1=once a month, 2=once a week...4=nearly every day). Right now, my ...
