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Questions tagged [kruskal-wallis]

The Kruskal-Wallis procedure is a nonparametric equivalent of one way analysis of variance, used for comparing the location of three or more groups; it extends the two sample Mann-Whitney-Wilcoxon procedure.

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4answers
42k views

Difference Between ANOVA and Kruskal-Wallis test

I am learning R and have been experimenting with analysis of variance. I have been running both kruskal.test(depVar ~ indepVar, data=df) and ...
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3answers
12k views

Is there an equivalent to Kruskal Wallis one-way test for a two-way model?

If the model does not satisfy ANOVA assumptions (normality in particular), if one-way, Kruskal-Wallis non-parametric test is recommended. But, what if you have multiple factors?
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1answer
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Post-hoc tests after Kruskal-Wallis: Dunn's test or 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-...
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1answer
9k views

Power analysis for Kruskal-Wallis or Mann-Whitney U test using R?

Is it possible to perform a power analysis for the Kruskal-Wallis and Mann-Whitney U test? If yes, are there any R packages/functions that perform it?
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1answer
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How to read the results of Dunn's test?

How do I read the results from Dunn's test? Specifically, what do the values in the table below tell me? I have non-parametric data in 4 groups, and I first did a Kruskal-Wallis test to confirm that ...
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2answers
9k views

Should I report non-significant results?

I've run a Kruskal Wallis test, and for some of the questions the p value is not significant. Would I report this in the same way as if it was significant, stating the df, test statistic and p-value? ...
11
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1answer
9k views

Multiple comparisons in a non-parametric test

I am working with a data set that is non-parametric and has 12 treatments. I performed the Kruskal-Wallis test and got a significant $p$-value, and now I would like to conduct a multiple comparisons ...
9
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4answers
16k views

Can Mann-Whitney test be used for post-hoc comparisons after Kruskal-Wallis?

I have a simulation where an animal is placed in a hostile environment and timed to see how long it can survive using some approach to survival. There are three approaches it can use to survive. I ran ...
9
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1answer
18k views

Friedman vs Kruskal-Wallis test

I have read the Wikipedia pages for Friedman's and Kruskal-Wallis' test, but I am not sure which one to use. Are there differences in the assumptions?
9
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1answer
446 views

Slight inconsistency between the Kruskal-Wallis built-in R function and manual calculation

I'm confused by the following, and I haven't been able to dig up the answer elsewhere. I'm trying to learn R while doing some statistics, and, as an exercise, I try to double-check the results of ...
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2answers
3k views

Testing the difference of (some) quantile-Q between groups?

For some Y variable, that is divided into 3 groups (X), I wish to compare the groups and for the hypothesis that the 90% quantile is the same between all three groups. What tests can I use? One ...
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2answers
1k views

Benjamini-Hochberg dependency assumptions justified?

I have a data set where I test for significant differences between three populations with respect to some 50 different variables. I do this using Kruskal-Wallis tests, on one hand, and by likelihood ...
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4answers
37k 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
3k views

Multiple comparisons with many groups

I would like to determine if using multiple comparisons test would be appropriate for my data. I used the Kruskal-Wallis test to determine if there were differences in mean inhibition among $17$ ...
7
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1answer
4k views

Nonparametric alternative to ANOVA for testing the difference between several brand preferences

I have collected a data from about 200 customers on their brand preference of 5 international fast food chain shops. Each customer was asked to rank all the 5 brands from highest to lowest (5 for the ...
7
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1answer
140 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 ...
6
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2answers
12k views

Do we need to report the median or the Mean when using a Kruskal-Wallis test?

I have two groups. There is a significant difference according to the KW test. But do I need to report the mean or median of the groups?
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4answers
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Contradicting p-values for Anova and Kruskal-Wallis on same data: Which is right?

I have a data file with task duration values for three groups, and I want to determine group effect on task duration (tasks were executed by individuals; each group had 7 different individuals; each ...
6
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4answers
2k views

Strange result of post-hoc test

I have data for a test on three groups. The measured variable is ratio scaled. The R code is g1a<-c(7, 3, 40) g2a<-c(1,1,2) g3a<-c(0,0,0) Since the ...
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2answers
3k views

Jonckheere-Terpstra interpretation

I am running the Jonckheere-Terpstra in place of Kruskal-Wallis test, as my factor is in ordinal scale (i.e. groups can be ordered). The Asymptotic significance (2-tailed) is 0.000, so it seems there ...
6
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2answers
3k views

Analyzing repeated measures experiment with multiple treatment groups and multiple measures

I am doing a study to evaluate the effect of two dietary supplements on body composition. Literature suggests that Treatment 1 (Dietary Supplement 1) affects body composition with some side effects ...
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1answer
625 views

Comparing unbalanced groups with ANOVA/Kruskal-Wallis when one group has only 1 observation

I would like to compare a continuous variable across 5 health status groups, but one of the groups has only 1 observation. Would an ANOVA/Kruskal-Wallis be valid? What can I do about the group with ...
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2answers
6k views

What is the difference between various Kruskal-Wallis post-hoc tests?

[There seem to be a lot of similar questions here, so please point me the right direction if this has already been answered, but I think it's reasonably differentiated.] There are many different ...
5
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1answer
11k views

Are pairwise Wilcoxon tests a valid non-parametric alternative to Tukey's HSD test?

I am trying to identify significant differences between groups from normal and non-normal distributions. When the distribution is normal the workflow is pretty straightforward: ANOVA and after that a ...
5
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2answers
4k views

Kruskal-Wallis test data considerations

I'm about to apply Kruskal-Wallis test (non-parametric ANOVA) on three groups of unequal length. I was taught/advised to apply Krukal-Wallis only if: dependent variable is at least at ordinal level ...
5
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2answers
182 views

Something more powerful than Kruskal-Wallis Test?

I have a sample from a continuous variable under 3 treatments and I want to assess treatment differences in the location of the underlying distributions. One option is to run a non-parametric test ...
5
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1answer
711 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
3k views

Disagreement between normality tests and histogram graphs

My data consist of compaction measurements from 3 different cell types (X,Y, and Z). My goal is to know whether there are "significant" differences between these measurements, so I have tested for: ...
5
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1answer
5k views

Differences between Dwass-Steel-Critchlow-Fligner and Mann-Whitney U-test for a post-hoc pairwise analysis

If you have one control and four groups of patients with a non-normal small sample size, there are differences in these tests for a post-hoc analysis after Kruskal-Wallis?
5
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1answer
1k views

Kruskal-Wallis test: how to calculate the exact p-value?

I would like to calculate the exact p-value of a Kruskal-Wallis test. How can I do it? Is it a huge computational task? Imagine I have something like that: ...
5
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1answer
378 views

Comparing classification results from models selected differently with Kruskal-Wallis

For a seminar at university I'm reviewing a paper that proposes a new feature selection algorithm. The authors also evaluated their algorithm by applying it beside two other feature selection ...
5
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3answers
468 views

Similarity of time series

I try to find out the smallest window size for calculating statistical values on a stream. To illustrate my problem: I record the average car counts per brand on a street using different sliding ...
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2answers
1k views

Post hoc for Kruskal-Wallis Test

What post hoc test can I do after Kruskal-Wallis? Is there a post hoc test for non-parametric test? Some says there's none. I ran Kruskal-Wallis test and as a result the null hypothesis was ...
5
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1answer
2k views

Reporting significance in Kruskal Wallis test

I performed the Kruskal-Wallis one-way ANOVA by ranks on five groups of data using Dataplot software. The software corrects for ties and uses Conover's procedure to do pairwise multiple comparisons. ...
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2answers
841 views

Why am I getting inconsistent results from Wilcoxon signed rank test and Kruskal-Wallis test?

I am doing a study on 3 drugs, comparing response pre-post treatment. My objective is to know if these drugs are effective and which one is better. I used non parametric tests since the results weren'...
4
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3answers
1k views

Same p-value. Is it normal?

I did the following comparisons with a Wilcoxon test on MatLab, and I got the same p-value on both. Is this normal? Is there something wrong? Also, the tests indicate not to reject H0. How to ...
4
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2answers
2k views

Kruskal-Wallis test: assumption testing and interpretation of the results

There is a chapter on the Kruskal-Wallis (KW) test on the website influentianl points, and there are some quotes I'm not sure I understand correctly: Quote 1: Some authors state unambiguously ...
4
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2answers
704 views

Is it possible to calculate a confidence interval related to a significant p value from the kruskal wallis test?

I have run the nonparametric Kruskal Wallis test with pairwise comparisons in SPSS to understand if my 3 groups of survey participants were different in their responses to a range of 5 point ordinal ...
4
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1answer
4k views

Appropriateness of K-S test and Kruskal-Wallis for assessing medical data set

I am analyzing some stats for a paper I am writing. I have statistics help available through my faculty but am not there for a couple of months so hoping you can help out. n = 463, 2 patient groups( &...
4
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1answer
115 views

Can Kruskal-Wallis be applied in this case?

In my experiment, I follow up 3 different groups of embryos for 12 timepoints. Each group has about a 100 embryos and I calculate the frequency (continuous variable) for each and tabulate the data for ...
4
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2answers
28k views

Kruskal-Wallis and post-hoc analysis in R

Although I know there are several post in this forum that are about this topic, none of them was useful in my case. I have the next data: ...
4
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1answer
722 views

Kruskal Wallis test with high type 1 error

using this code ...
4
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0answers
191 views

multiple Kruskal-Wallis instead of ANOVA for non-normally distributed data

Apologies in advanced if I supply too little or vague information, since I am a complete newbie in stats and using this forum. So I did a study which evaluated psychopathic personality traits, ...
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2answers
2k views

Any other non-parametric alternative to Kruskal-Wallis?

It looks like Kruskal-Wallis is the standard nonparametric test for more than two groups. The problem is that it does not tell which groups are different, except that whether there exists significant ...
3
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2answers
3k views

Kruskal-Wallis test is not significant but some of the Mann-Whitney comparisons are significant

I have a non-normalized dependent variable and an independent variable broken down into 4 groups. As such, I used the Kruskal–Wallis analysis to look for significant differences in the ranks of the ...
3
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1answer
6k views

Bonferroni correction on multiple Kruskal-Wallis tests

My data consists of 3 groups, and 6 variables. The data are not normal so I want to use non-parametric tests to uncover significance. The first thing I wanted to get your opinion on is, is it ...
3
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4answers
13k views

Non-parametric test for unequal samples with subsequent post-hoc analysis?

Is it okay to perform a Kruskal-Wallis on four unequal samples? Further to this, is there a subsequent pair-wise post-hoc suitable for two unequal sample sizes?
3
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1answer
346 views

Mann-Whitney U test or Kruskal Wallis test for comparing median of two groups?

I know that Kruskal Wallis test can be used to compare median of two or more groups (e.g. see this link: https://www.statisticshowto.datasciencecentral.com/kruskal-wallis/ ), and that Mann-Whitney U ...
3
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1answer
421 views

Permutation test for two distributions with the same mean but unequal variance

I am using the coin package in R. For two distributions with the same mean but different variance, the test is unable to reject the null hypothesis that the two ...
3
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1answer
959 views

Non-normal distribution even with Kruskal-Wallis test

Thanks to anyone who can help! I`ve done a survey with Likert-scale questions with about 1,500 participants. Initial analysis in SPSS showed no outliers (using box-plot) but scores were not normally ...