Mann Whitney U / Wilcoxon Rank-Sum Test in R | R Tutorial 4.3 | MarinStatsLectures October 21, 2019 30 By Stanley Isaacs

that is really helpful video. excellent! I was wondering how to use R studio for newbie like myself.

Great to hear! We've got plenty of intro level R videos and are always producing more…

Nice video, thank you!

Very nice..Thank you so much..it is quite educative video.

very clear and helpful!

Very useful tutorial. Straight forward, and emphasis on useful options and test statistics in R output.

Very helpful

Awesome, super clear!

Hello Mike, the video is pretty clear and easy to understand. I tried to use the same code to conduct the Mann-Whitney of my dataset in R studio. But it generated the error:"Error in wilcox.test.default(., RminTTC ~ as.numeric(Vehicle.pair), mu = 0, : 'x' must be numeric". I checked the class of those two variable and they are indeed numeric. So I have no idea how to solve this problem. Could you leave your email to me and help me? Thank you very much!

Hi Mike, I'm trying to compare distance values of two groups but I get this error:

Error in wilcox.test.formula(A ~ D, alt = "two.sided", exact = F, :

grouping factor must have exactly 2 levels

The two groups (A and B) have n=30 of different values.

Hello, Mike. I have questions to ask you for help, if you are free.

I am doing toxicity test. I want to compare control versus different treatment groups in a series tests, since I want to know if there are any significant differences.

In one of my test:

there are 5 individuals in an experiment unit, and 4 duplicates for each treatment. So totally there are 20 individuals. SO 5 individuals in the same experiment unit are integrated together in statistical analysis. Two variables in the comparisons: dose and incidence of malformation (sometimes this variable is mortality). I want to ask which type of test I should adopt: 1). if there is significant difference in incidence of malformation because of different doses; 2). if there is significant difference in incidence of malformation because of difference chemicals but same dose.

Thanks a lot! Sorry to trouble you.

Thank you for this very straightforward video. I want to use the Wilcoxon Rank Sum Test as a Post hoc test after Kruskal-Wallis-Test. I have 6 groups to compare. I found the command "pairwise.wilcox" for that, is that the Mann-Whitney-U-Test as well?

Thanks so much for explaining this so clearly. I was wondering in the context of the video whether the numbers of either factor being tested within the set can effect the validity of the p value being produced. Specifically: does the fact that there are more non-smokers in the sample then smokers reduced the validity of rejecting the null-hypothesis? I'm working with a similar set of data (in that one factor I'm testing for has a higher frequency then the other) and was wondering if this is accounted for in the test.

Great video, very illustrative. Is there any non-parametric test that I could use to assess differences between two groups using an independent covariate?

Thanks!

Thanks for the clear explanation. May I know if I could still proceed with the test if there are some plots outside my boxplot which seems like outliers?

Fantastic video and incredibly straightforward. Question: How do you run the same test if you have a differing numbers of observations? For example, imagine I have four variables from seven locations each with a different number of observations. How would I conduct the test?

Excellent! and straight forward

Great video! I need to know what test to use in R when data is non-parametric but is ONE-SIDED. I tried this in R with the wilcox.test but an error is computed informing me that the argument must be two-sided. Thanks.

Thanks for all the awesome videos! While I've followed all your tutorials to the T, I keep getting a very different w and p value after entering the wilcox.test command. Can you help me sort out what's going on please?

It comes out looking like this:

wilcox.test(LungCap ~ Smoke, mu=0, alt="two.sided", conf.int=T, conf.level=0.95, paired=F, exact=T, correct=T)

Wilcoxon rank sum test

data: LungCap by Smoke

W = 1, p-value = 0.5714

alternative hypothesis: true location shift is not equal to 0

71.42857 percent confidence interval:

-5.325 1.000

sample estimates:

difference in location

-3.775

Warning message:

In wilcox.test.default(x = c(6.475, 9.55, 11.125, 4.8, 6.225, 4.95 :

Requested conf.level not achievable

what is 'mu' in the syntax and why is it taken to be zero?

Thank you so much. Could you please teach about "how to apply a Wilcoxon test for ALL variables in columns at a time" (values of two groups are in the same column)?

But how to check that they are not parametric

Hey. Thanks for the video! How does one correct for covariants, such as age, using Wilcoxon rank sum test?

Thank you very much for the video. I have a question, can I study the interaction between two variables (let's say sex and age in your example) using the Wilcoxon Rank-Sum Test?

Thanks for the wonderful explanation

👋🏼 Hello there! In this R statistics video we learn to conduct the Wilcoxon Rank-Sum aka Mann-Whitney U test in R. This test is the non-parametric alternative to the independent t-test. Wilcoxon Rank-Sum (Mann-Whitney U) test is appropriate for examining the difference in medians for two independent populations. The LungCap R dataset that is used in this video is available here: (https://statslectures.com/r-scripts-datasets) ! If you like to support us, you can Donate (https://bit.ly/2CWxnP2), Share our Videos, Leave us a Comment and Give us a Like ! Either way We Thank You!

Hello, Mike, thank you for the video, it is great and useful to me. I have a question, I have samples from two group, but the observation is not equal (n1=40, and n2=150), one of that does not follow the normal distribution, can I use Wilcoxon test? If not, what should I use? Thank you very much.

Hi Marin, thanks for excellent and straightforward videos. I am now to R and I think that I meet the right page :). May I know if you have video on performing comparison of "more than two" nonparametric groups? I think it is equivalent to TukeyHSD test for parametric test. I could not find this video. Many thanks!

Can you make a video on how to find nth largest value of particular variable and print the whole Information about that particular case