The Mann-Whitney test is a non-parametric rank test to assess "whether one of two samples of independent observations tends to have larger values than the other" [Wikipedia].

learn more… | top users | synonyms

0
votes
0answers
9 views

Non-normal, related but non-paired data, test for significant difference

i am comparing the profit margins for restaurants prior and post gaining a michelin star. I have all the profit margins for each restaurant up to 2-5 years prior and post. I want to compare all of ...
0
votes
2answers
43 views

How do I get which experiment is doing better using the Mann-Whitney U Test?

The material I got only described how to test if there is difference (null hypothesis: H0 = H1). However, what I want to test is if the test version is doing better than control: null hypothesis: H0 ...
0
votes
1answer
49 views

Is the Mann-Whitney U Test appropriate for assessing the busiest day of the week?

We have ten years of data where the average overall reveals that Monday is the busiest with the most visits to the hospital. We would like to provide a p-value to support that observation. Given ...
0
votes
0answers
12 views

FDR correction of Mann–Whitney U test

I have applied the limma moderated t-test on some proteomics data, on the label free quantitation values of proteins between control and exposed groups (2 samples each). Limma outputs p-values and the ...
0
votes
0answers
31 views

Am I using the Mann-Whitney U test correctly?

I have two samples of online articles of different forms (one sample contains posts without infographics, and the other with infographics). Sample 1 (w/o infographics): n = 4993 Sample 2 (with ...
0
votes
1answer
30 views

How is the Mann-Whitney U statistic calculated in SPSS?

I get different results using NPTESTS and NPAR TESTS in SPSS for the U-statistic. Can someone please tell me which formula is used for these two procedures, respectively. It looks like NPAR TESTS ...
0
votes
0answers
26 views

Any alternatives to Kruskal-Wallis and post-hoc tests?

I have non-parametric data comparing people's sense of community scores who use different modes of transport to travel I want to see if there are significant differences between the three modes of ...
3
votes
2answers
59 views

How to interpret Mann-Whitney's statistical significance if median is equal?

Testing the difference between the observations of two groups by using Mann-Whitney Test has given the following output (from minitab): ...
1
vote
1answer
34 views

Can increasing the significance level help to avoid detecting minor differences in large datasets?

In the accepted answer of THIS question, it is stated that "With such large sample sizes both tests will have high power to detect minor differences". On the other hand, a voted up comment in THIS ...
0
votes
1answer
29 views

Can I validate results after statistical hypothesis testing?

I have data from one clinical test for 450 patients. Depending upon my objective, I divided data into 7 different categories to compare two groups, in each category (inherited from parents and not ...
0
votes
0answers
29 views

Multiple comparisons when preforming a t-test and Mann-Whitney U test

I have 90 proteins(column) and about 170 samples(rows) with data. The data describes protein levels for 90 different proteins. Every samples is also in a group, A and B. I would like to preform a ...
0
votes
1answer
35 views

Help determining a statistical test to use

I have a data set that has the ages, weights and heights for 444 Olympic athletes. I'm wanting to compare each of these to whether or not that athlete won a medal and see what the correlation is and ...
0
votes
0answers
10 views

What Would be the Best Statistical Test?

I want to see if the fiscal year end densities for public and private companies come from different distributions. The null being two samples come from the same population and the alternative being ...
3
votes
2answers
66 views

Mann-Whitney (U) Test at N>20

I am a high school Psychology student. I just performed a study where two separate groups of sizes 26 and 28 took the same test under different conditions. For the data analysis my professor has ...
1
vote
0answers
15 views

Why I receive a n/a sign with a Wilcoxon rank-sum test calcualtor? [closed]

I was wondering why I receive a n/a sign with a Wilcoxon rank-sum test calcualtor. I used a calculator find from internet but I cannot understand the n/a interpretation. Here is a screenshot: Does ...
0
votes
0answers
11 views

Non-parametric tests for different measurement scales?

Not sure if I'm expressing this correctly. I've done a survey of my statistics class. I've collected the following information Mathematical knowledge before taking course, coded as 1 (basic), 2 ...
0
votes
0answers
17 views

Minimum sample for non parametric test?

Exactly how many sample to be minimum size for non parametric test? Right now i have 3 data with really2 small sample size 1. 5 pairs for wilcoxon signed rank test (pretest and postest in 1 place) 2. ...
0
votes
0answers
28 views

Direction of Mann-Whitney significance test result

I have conducted a Mann-Whitney $U$ test to identify if there is a significant difference in ranking (on Likert scale) of a dependent variable between two groups of people: e.g. those who have <5 ...
0
votes
1answer
47 views

Is Mann-Whitney U test valid for unequal non-normal dataset? If not, what is?

Summary: I have a population of people split randomly into seven distinct cohorts, amongst whom events occur each month with varying frequency. We have made the same environmental change across all ...
2
votes
1answer
64 views

similarities between t-test ,welch test and mann whitney test

I am newbie to statistics field. I find it is quite hard to understand this few tests even though they are common tools for testing hypothesis. As i am referring this paper actually "should we always ...
1
vote
1answer
47 views

is mann whitney an alternative to t-test?

can i compare both of them ? As i may change the sample size , variance and also skew the distribution. However,some researcher claimed that comparing both of them couldnt make sense as it is just ...
1
vote
2answers
112 views

How to validate k-fold cross validation results for classifiers?

I've applied 6 classifiers on my data set using 5-fold CV to calculate average AUC for each model. What method do you suggest me to determine which model has the highest AUC? I've heard of t-test and ...
0
votes
0answers
48 views

Test for systematic difference between two samples

I would like to now if there is a significant difference in the two samples a & b. It is not important for me to know which way the difference is, just if there is one. The two samples can include ...
5
votes
2answers
130 views

Comparison of medians in samples with unequal variance, size and shape

What am I trying to do and how does my data look? I am trying to perform some comparisons of medians of groups of data that, most often than not, are not-normally distributed. In some cases I am ...
0
votes
1answer
37 views

Mann-Whitney significance and multiple hypothesis testing significance

I am performing various comparisons using the Mann-Whitney U test. Because I'm comparing various groups simultaneously, I would am also correcting the p-values for multiple hypothesis testing using ...
2
votes
1answer
42 views

Significance level as function of sample size in Mann Whitney

I was reading this question and answers and this blog post and I was thinking about the minimum significance level that could be achieved by comparing two populations whose medians are statistically ...
0
votes
0answers
15 views

Understanding relations in non-normal distributed observations

I am struggling to pick the right statistical test(s) for data created by a simulation. An excerpt of the data is as follows: ...
2
votes
1answer
54 views

Mann-Whitney with many zeros

I'm running a basic Mann-Whithney U test in R between two groups; each group represents the abundance values of a particular bacteria within an animal. Therefore a 0 means that bacteria is not ...
0
votes
0answers
21 views

Different correlation inside groups with same population

I'm analyzing data from >100 subjects randomly assigned to two groups. Each subject has a skill level and a self-evaluated skill level (the latter being the subject's own perception of the former). ...
1
vote
0answers
46 views

Choose between Mann-Whitney test and Wilcoxon?

I'm practicing this test and I have a trouble with this question: Students' scores on the mathematics test are given in the following table. The students are divided into two groups: those who ...
1
vote
1answer
77 views

Interpret Wilcoxon-Mann-Whitney Result in R [duplicate]

I am doing a Wilcoxon rank sum test (aka Wilcoxon-Mann-Whitney) with R. There are two variables "ScorePerView", that is metric and "HasCodeElement", that is binary. So the syntax is like that ...
1
vote
0answers
220 views

What statistical analysis should I use for this (attached) dataset?

I have a dataset of 815 positive examples and 9492 negative examples for a certain class. Each example is represented by 12 features and a target label (i.e. TRUE/FALSE). The dataset is in a CSV file ...
0
votes
0answers
31 views

Mann-Whitney U test with different distribution shapes

I have collected the following data (mean numbers of animal passes per hour) during 18 samplings performed independently (non matched) in two different areas. Both data distributions are positively ...
1
vote
1answer
143 views

Correction for Multiple comparisons using Mann-Whitney U test

I am using Mann-Whitney U tests to compare groups of high and low relationship quality on five psychological outcomes. My data is non-normally distributed which is why I am using Mann-Whitney U tests ...
0
votes
0answers
51 views

How do one interpret the results of wilcoxon-mann-whitney test in SAS?

I have done the Wilcoxon test in SAS. My class variable is race. I got a low p-value. What exactly does that mean?
0
votes
0answers
38 views

Statistical test with unequal sample sizes

If I have two samples with vastly different sample sizes (say n1 = 800 and n2 = 21,000) what statistical test would give me the most reliable results? I've been using the Mann Witney U test. Is the ...
1
vote
0answers
38 views

Combining data from different locations to test difference in populations

I have (irregularly spaced) times series concentration data for four locations and am trying to discern whether or not there has been a change in concentrations after a particular event. To avoid ...
3
votes
1answer
243 views

Multiple comparisons after Kruskal Wallis using the FDR approach. How to compute P values (Dunn or Mann-Whitney)?

I want to allow users of GraphPad Prism to use the False Discovery Rate (FDR) approach to multiple comparisons after nonparametric one-way ANOVA (Kruskal-Wallis). The idea is first to compute an exact ...
1
vote
0answers
55 views

For Mann-Whitney, should I report effect size or Hodges-Lehmann pseudomedian?

When reporting a Mann-Whitney-U test result, is it better to report it's effect size or the Hodges-Lehmann pseudomedian (as R give us as "difference in location") ?
1
vote
2answers
68 views

Interpreting contradicting results T-Test vs. Mann-Whitney test (2 independent samples)

I want to test if two indepent experimental groups are sign. different in terms of one outcome variable, but face the following questions: Basic setup 2 groups with 200 observations each Outcome ...
0
votes
0answers
18 views

Comparing Peptide Amino Acid Composition: 2 Independent groups, Non-normal data, discrete data

I have two large groups of peptides, "positive" group (n = 368) and "negative" group (n = 880). The average length of the peptides (in each group) is about 20 amino acids. What I am trying to do is ...
1
vote
2answers
133 views

Relationship between ROC curve and statistical significance in comparison of two groups

My question is about any possible relationship between the significance of a comparison test (Mann-Whitney U) and the ROC curve. If the comparison test is strongly significant, should we expect a ...
0
votes
0answers
28 views

Which test to use: Mann-Whithney U or Spearmans rho or both?

I have the following question: I have a sample group, which is divided in to two subgroups: "good" and "bad" people. I have their points achieved in an IQ test. Points are grouped into 4 categories ...
2
votes
1answer
98 views

chisq.test and wilcox.test don't concord with my graphs and observations?

I want to know if a factor variable have an incidence on another variable (dura). For example : ...
1
vote
2answers
61 views

How to adjust for multiple comparisons with 2 groups where several outcomes were measured?

I have two groups, Controls and Patients, with 6 measurements for each such as speed, amplitude and so on. I'd like to examine whether these measures are different for the 2 groups. So firstly I'd ...
0
votes
1answer
69 views

Similarity between two small datasets

I have gone through several test's (Kolmogorov-Smirnov, t-test, u-test etc..) but I am not sure which one to use when it comes to comparing two small data sets, lets say of size 10 each. ...
1
vote
0answers
29 views

Testing data for Same Shape

I want to run a Mann-Whitney test on 2 arbitrary sets of data but I read that one of the assumptions of the Mann-Whitney test is that the data is the same shape. How can I test if the 2 sets of data ...
0
votes
0answers
40 views

Mann Whitney U test adjustment

Let's say I have 2 separate samples and each sample has 20 observations and I'm using the Mann Whitney U test. As I understand it from wikipedia, I can calculate a z-value that can be converted to a ...
4
votes
1answer
59 views

Why exactly is normality an assumption in a T-test but not a Wilcox rank sum/Mann Whitney U test when obtaining a p-value?

In addition to the question, please do correct anything below that I have incorrect. I understand how the test statistics for a t-test and WRS/MWU test are calculated. In a t-test, $t=\frac{\bar ...
0
votes
0answers
50 views

Which statistical test to use on mean data?

I have sets of data from two sample A and B. the data in sample A and B are the average mean of the population sample. Examle, sample A has list of data. each data in he sample is a an average value ...