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].
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is there something like Mann-Whitney U test that can control for a continous variable?
I want to compare mean inhibitory concentration (continous variable) in patients with outcome A versus outcome B. I used Mann-Whitney U test. However I would like to control those results for the ...
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20 views
Is it justified to say after U Mann-Whitney test that there is a “possibility to differentiate”?
I have 2 variables (similar measurement of 2 structures in same individual) with non-normal distribution, so I compared ranks with U Mann-Whitney test. The result was significant (p=.01). Is it ...
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1answer
43 views
how to analyze pre-post attitudinal data (ordinal) collected from a group of 60 students?
I have a survey with 25 items that were administered pre and post an intervention. Each item had four possible responses: (1) Not Appealing at all; (2) Not Appealing; (3) Somewhat Appealing; and (4) ...
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1answer
32 views
Does alpha need to be adjusted for running Mann-Whitney U test independently for two dependent variables?
I am comparing two group means on two dependent variables (aggression and stress levels) using Mann-Whitney U test by SPSS. My question is that do I need to adjust the alpha level for this?
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2answers
116 views
Mann-Whitney null hypothesis under unequal variance
I'm just curious about the null hypothesis of a Mann-Whitney U test. I often see it stated that the null hypothesis is that two populations have equal distributions. But I'm thinking - if I had two ...
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1answer
120 views
Independent paired t-test -> Mann Whitney U
Just a quick introduction, I'm rubbish at stats.
I asked a question before which was very well answered but I have since modified the experiment in a way that confuses me as to which test I should ...
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1answer
54 views
T-test on ranks vs Mann WHitney U-test equivalence
What does it mean when people say that a T-test performed on ranked data is equivalent to a Mann WHitney U -test? Does that mean they just test the same hypothesis/are useful in the same situations or ...
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1answer
49 views
Randomization Tests
The following data are mandible lengths (mm) of 10 male and 10 female golden jackals Canis aureus in the collection at the British Natural History Museum. The two samples are independent.
...
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78 views
When to use a chi-squared test?
This is a very basic question however I do not have a statistical background and I am currently analysing some data for my dissertation.
I have constructed a survey about healthy lifestyles & ...
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58 views
is the Mann Whitney U test appropriate for my data?
I have data from a survey I designed for my dissertation on obesity and public health. The questions are mostly qualitative in nature.
For example,
How healthy do you consider your lifestyle to be? ...
2
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1answer
164 views
ANOVA on ranks vs. Mann-Whitney U test
What exactly is the difference between performing a t-test on data that has been ranked and performing a Mann-Whitney U test on the unranked data? I keep reading things like:
For example, the ...
2
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1answer
237 views
Mann Whitney or two tailed t-test
I am new to statistics and am in need of some help. I am running a study where I am providing two groups with surveys to test for their perceptions using a Likert Scale. One group I'm testing prior to ...
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2answers
199 views
p-values of Mann-Whitney U test identical for raw and log-transformed data
I am new to Stats and came across this problem while running my analyses on SPSS which I cannot explain.
How is it that even after transforming my data by logging it, it still has the same p-value ...
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2answers
71 views
How to correct for gender in Mann-Whitney U test?
My statistical knowledge is very limited.
I have two groups (patients and controls) and a measured concentration value for each indivdual. Not normally distributed: Mann-Whitney
How do I correct for ...
3
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1answer
121 views
Student's t vs Mann-Whitney U
Trying to choose between these two tests for data I've harvested from Android store. Basically, I want to see if there is any difference in the number of dangerous permissions requested by free vs ...
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0answers
130 views
Wilcoxon-Mann-Whitney Output
I proposed a question early on infection rate data in 6 different hospitals for two years (N=12). After speaking with several people I decided that a Wilcoxon-Mann-Whitney (Mann-Whitney U, Wilcoxon ...
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2answers
211 views
Mann-Whitney for non-normal distributions with n>20?
I have 12 groups of datasets (mostly non-Normal, quite right-skewed), and I would like to see if there is a significant difference within each pair. (But the data itself is not a paired dataset, as in ...
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1answer
500 views
Mann-Whitney U test and K-S test with unequal sample sizes
I want to compare two distributions, to see if they are significantly different. They represent task time completions (so they range from 1 to around 1000 seconds) in two different months. They are ...
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1answer
223 views
What statistical test should I use to assess rate of photosynthesis in leaf discs?
My biology test is to measure the rate of photosynthesis in leaf discs. It's a simple experiment where I will infiltrate the leaf disc space with sodium-bicarbonate and cause a pressure difference to ...
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1answer
339 views
T-test or Wilcoxon signed rank or Mann–Whitney U
A magazine wants to know if the online viewers are more than its printed copy buyers.
Which statistics test is the best to use, the t-test or Wilcoxon signed rank or Mann–Whitney U?
If I have ...
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2answers
84 views
Statistical comparison of two means with a range not starting at 0
I don't know the exact term for this, so googling didn't work. I will explain exactly what I need below.
I want to compare two sets of values such as blood sugar or blood pressure, where the values ...
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0answers
30 views
Help on Statistical analysis of Profits
We have been working on a project where we have 2 or more trading agents on a market stock and for the outcome we have the profits that each trader generated after running 1000 times or more each ...
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0answers
130 views
Non parameteric tests for 2*2 mixed design
I have 2*2 mixed design, where the two factors are time and group. The time levels are pre- and post-intervention, and the group levels are control and intervention.
If I were using a parameteric ...
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1answer
188 views
Mann-Whitney test with ties
I have two data sets with PDFs roughly like this:
$$
p(x) = \left\{
\begin{array}{lr}
.75 & x = 0\\
\text{Lomax}(x) & x > 0
\end{array}
\right.
$$
i.e. it's ...
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1answer
106 views
Non-Parametric Test controlling for third variable
There are two laboratories measuring identical samples. One of the lab's data is non-normal, therefore I am looking for a non-parametric test.
After comparing overall differences in the dependent ...
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4answers
489 views
Choosing between logistic regression and Mann Whitney/t-tests
I have a dichotomous variable $A$, which does not have an a priori determined proportion of 0's and 1's, and a continuous variable $b$.
In scenario 1, I decide to designate $A$ as the independent ...
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0answers
63 views
Statistical test for two-factor heteregeneously distributed samples
Data
I have a sample size of 50 in group A and 50 in group B where groups A and B are unmatched. Each sample in group A and group B has two frequencies associated with it, which I'll call $x$ and ...
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1answer
335 views
Fisher's exact test for results of Wilcoxon-Mann-Whitney
I have two groups of subjects (9 and 13 people). And data from two condition for this groups. In each condition for each subjects I have some measurements. But number of measurements are different for ...
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2answers
203 views
How to test group differences when neither parametric nor nonparametric assumptions are met?
Consider following example. We asked 50 men and 50 women one question and they answered on 5 point likert scale (1 is completely disagree and 5 completely agree).
Suppose that 50 men responded 20 ...
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1answer
419 views
Which test should I report, ANOVA or Mann-Whitney?
My data set is small, with roughly 12 in each group (two groups). In addition, the distribution of the data is not normal. As a result, I ran a Mann-Whitney U test.
However, I also ran a one-way ...
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1answer
262 views
Comparing P value from t test vs. Mann-Whitney test
If you analyze the same data with a t test and the nonparametric Mann-Whitney test, which do you expect to have the lower P value?
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3answers
2k views
Which result to choose when Kruskal-Wallis and Mann-Whitney seem to return contradicting results?
I have these groups where the values are responses to a 10-point Likert item:
g1 <- c(10,9,10,9,10,8,9)
g2 <- c(4,9,4,9,8,8,8)
g3 <- c(9,7,9,4,8,9,10)
...
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1answer
1k views
Which W to report for the Wilcoxon test?
Imagine that I have the following data:
GroupA <- c(2,4,3,1,2,3,3,2,3,1)
GroupB <- c(3,5,4,2,4,3,5,5,3,2)
Then when I call in R
...
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0answers
49 views
Assessing difference observations of two samples
I have two continous samples: background and data. I want to check whether data observations are significantly greater than background. I used U-Test to calculate p-value, but now I want to find a ...
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1answer
169 views
Some questions about two-sample comparisons
I am applying some statistical tests using python's scipy.stats library to some datasets that I have (taken in pairs), testing whether they both come from the same unknown distribution.
I don't have ...
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1answer
93 views
How to test that a set of distributions are located in a given order?
I have a set of population distributions; I obtained them empirically, computing histograms from very large populations (about 1 million per distribution). The population distributions might not have ...
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1answer
115 views
Estimating Diversity of operon types using HMMs across metagenomes: Mann-Whitney? Kruskal-Wallis? or other?
Question that seems complex but probably isn't.
I'm comparing 10 metagenomes (http://en.wikipedia.org/wiki/Metagenomics), that are supposedly unrelated (they are 10 geographically separate ...
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0answers
292 views
Multiple comparisons process using Kruskal-Wallis, G-Test and corrections
I want to know if changing a button color has a positive effect on different measures (see the 4 measures below), using the following process:
There's a default button, which is the fixed control ...
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2answers
755 views
Statistical Significant Difference between 5 groups of data
I'm trying to compare 5 different gears used by fishermen and the amount of bycatch found in each. The values have a unit of "% of time encountered" and range between 0% (ie: never have bycatch) and ...
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0answers
1k views
Difference between post-hoc test after Kruskal-Wallis and Bonferroni corrected Mann-Whitney tests
I have some non Gaussian distributed variable and I need to check if there are significant differences between the values of this variable in 5 different groups. I have performed Kruskal-Wallis one ...
3
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4answers
316 views
Comparing smoke and hormones level in two groups of people. Which test?
I'm totally not a pro in statistics so i hope the question is not too simple!
I have two groups of patients. One group are smokers, the second are non-smokers.
I want to compare the level of some ...
3
votes
4answers
1k views
Choosing the right test when comparing two groups: Mann-Whitney, Kolmogorov-Smirnov or other?
I need help, since my skills and knowledge in statistics are really limited.
Using Pearson correlation I found that there is some relationship between a binary one and a second variable taking values ...
4
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1answer
245 views
Bootstrap p.value, Wilcoxon rank sum or other test?
Imagine I have a network, and in this network I have n nodes of interest.
I calculated the average shortest path between these nodes.
I want to see if they are statistically significantly close to ...
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2answers
289 views
How to compare two non-randomly selected groups within a sample?
I am quite new to Statistics, so please do not flame me for such a simple question.
I made a controlled experiment and successfully gathered the data. 41 persons participated. They made a ...
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0answers
1k views
Why does one get a 0.000 Mann-Whitney U value (not p-value) etc.?
1) Is it okay to run a Mann-Whitney U test on unequal sample sizes i.e. two groups (N=11, N=12)or is there an alternative test?
2) What does it mean when one obtains a zero value for a Mann-Whitney U ...
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4answers
12k views
Minimum sample size for unpaired t-test
Is there a "rule" to determine the minimum sample size required for a t-test to be valid?
For example, a comparison needs to be performed between the means of 2 populations.
There are 7 data points ...
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2answers
4k views
When to use the Wilcoxon rank-sum test instead of the unpaired t-test?
This is a followup question to what Frank Harrell wrote here:
In my experience the required sample size for the t distribution to be
accurate is often larger than the sample size at hand. The ...
4
votes
1answer
299 views
What is the null hypothesis in the Mann-Whitney test?
Let $X_1$ be a random value from distribution 1 and let $X_2$ be a random value from distribution 2. I thought that the null hypothesis for the Mann-Whitney test was $P(X_1 < X_2) = P(X_2 < ...
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2answers
979 views
How to do a paired test when some cases have no pair?
I have a question regarding paired and unpaired tests. I know the difference between both tests. I am using R for Wilcoxon test. My test is a paired test, however the X and Y do not have the same ...
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2answers
1k views
Why is the Mann–Whitney U test significant when the medians are equal?
I've received a results from a Mann-Whitney rank test that I don't understand.
The median of the 2 populations is identical (6.9). The uppper and lower quantiles of each population are:
6.64 & ...
