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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192 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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1answer
646 views

how to interpret kruskal.test results with equal values

I have four samples (x1, x2, x3, and x4) as thier values shown below ...
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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 ...
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187 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 ...
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30 views

Help with choosing statistical test

I have a dataset consisting "Name of Power plant", "Year", "Status of compontent $1$", $\ldots$ "Status of compontent $n$", "Availability of power plant per year [%]", "Number of times the plant had ...
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80 views

What should be proper p value cutoff point for multiple comparison case?

I have 4 conditions, (Control, Stim-1, Stim-2, Stim-3) and 9 different proteins expression levels in each conditions. The sample number of each protein expression level in each conditions are about ...
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69 views

To what degree can normality be violated for one way anova?

i want to do anova but my data is not normal? i can run Kruskal-Wallis H test instead but the post hoc test for Kruskal-Wallis is not easily found.the skewness is 1.33 and kurtosis .536 of my data- ...
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1answer
738 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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477 views

kruskal wallis post hoc test for negative and positive values

I have 10 means and I want to test if there is a significant difference between the groups. The means are composed of cost values that can be negative and positive. I read here the kruskal test can ...
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1answer
97 views

Analyzing Gain Scores and/or correlation in a non-experimental setup

I am a teacher in a language program at a university, and I was interested in investigating whether or not there is a correlation between the number of sessions a student spends in our program and ...
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1answer
74 views

In medical statistics, when to use $\chi^2$ and when to use Kruskal-Wallis H?

I am conducting a retrospective analysis on the effect of three different treatment option (intervention treatment) on a special type of cancer, so I have three groups: 1, 2, and 3. In the baseline ...
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1answer
6k views

How many « degrees of freedom » should a Wilcoxon rank-sum test have?

I would like to perform a Mann-Whitney U Test (also called Wilcoxon rank-sum test) on a weighted sample in R. Such a non-parametric test is required, as neither of the two variables used follow normal ...
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2k views

Negative H value in Kruskal Wallis test

I've found exactly one source adressing this (and of course didn't save it). It said that in a Kruskal-Wallis this is a consequence of having a large sample with a lot of ties. Seen as I've got about ...
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1answer
743 views

Where does the number “12” comes from in Kruskal Wallis formula?

I just want to know.. Where does the "12" in the Kruskal Wallis formula comes from? I hope someone can give me a very good explanation.
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Kruskal-Wallis across 3 groups non-significant, but regression of the same data very significant

I have an issue regarding the significance of an association that I can't seem to get my head around, because using one statistical test it is significant and using another, it is non-significant (...
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Is there any test, like Mann Whitney U test or Kruskal Wallis test, that allows me to include a categorical covariate (like an ANCOVA)? [duplicate]

Here is my question: I want to know if there is a test that allow me to do an nonparametric ANCOVA. Let me explain: I am looking for a Mann-Whitney-U and a Kruskal-Wallis, but I want to include a ...
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199 views

Most appropriate test for count data

So I've performed an experiment whereby I had 12 1km transects. 6 of these were along rivers running through agricultural land and 6 through woodland. These were arranged in pairs so that each agri ...
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2answers
715 views

Comparing the means of 6 groups, binary dependent variable

I accomplished a field experiment which results in six differently treated groups (including one control group, each n = 300). Due to randomization all groups are expected to be equal in terms of ...
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51 views

Ranking data sets by means etc. (unequal sample size and variance)

I want to rank several lists of data by their tendency to be larger or their capacity to be larger when extrapolated. Is there a way to do this effectively?
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1answer
900 views

Significant Result in Levene's Test

I am very confused right now. I ran Levene's test on my data and got a p-value of 0.000, meaning that variances are very heterogeneous. I transformed the data but no method can make them homogeneous. ...
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1answer
111 views

R how to get same sample size from different categorical values [closed]

I have an unbalanced set of records for different values of a categorical variable as shown below: ...
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1answer
187 views

Kruskal-Wallis: how to handle ties that might not be really ties?

I have data from a mass spectrometer that are precise to 6 decimal places and range from 0.1 to 10. However, some items cannot be measured by the mass spectrometer because they are "below the limit of ...
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1answer
1k views

Chi-squared or Kruskal-Wallis?

If I collect data for both a control and an experiment group, what tests would I use to detect a significant difference between groups in: 1) numbers with wound healed at week 4, week 8 and week 12 ...
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432 views

Does Kruskal-Wallis need multiple comparisons correction?

I have three groups and aproximately 500 independent variables. I wanted to know if I had to do any multiple comparison correction (e.g. Bonferroni or Benjamini-Hochberg) on the p-values obtained with ...
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1answer
211 views

ANOVA (assuming different distributions) vs Kruskall-Wallis and post-hoc tests

During stats courses on Uni I learnt (if I remember correctly and hopefully don't put my teachers to shame) that if you want to compare multiple groups with eachother you look at the residuals of an ...
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1answer
66 views

converting a chi-square with more than one degree of freedom into a pearsons r

I want to run a power analysis for a study using correlations between two continuous variables. Previous research with the variable I am interested in used a Kruskal-Wallis test to look at differences ...
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1k views

Chi-Square value in Kruskal Wallis test very large

I am comparing measurements of 12 different groups to one another. My distributions are not normal and my Levene's test is significant - even after data transformation. I am therefore doing a Kruskal-...
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1answer
596 views

Kruskal Wallis for binary data

I have collected data from three groups (with different sizes of n). This was done with a test instrument consisting of 9 items, each binary coded (1 = right, 0 = wrong). The results are not equally ...
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2answers
651 views

Kruskal Wallis or Manova

I have to analyse 8 independent variables (IV) toward 8 dependent variables (DV) in my research. The IV is nominal while DV are ordinal (likert-scale). I run the normality test and the result is zero (...
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1answer
40 views

Count data with three response types

I administered a test to three groups of people. They had to choose the correct answer between four choices provided. Only one choice is correct and the other three are wrong answers. There are forty ...
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633 views

Difference in mean between two periods in a time serie? What test to use?

I have a dataset of multiple experiments measured each hour, for 56 hours. Now I want to identify if there is a significant difference in the mean value between the time periods 1-2 hour and 50-57 ...
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2answers
3k views

Adjusting for Confounding with Kruskal Wallis?

I have a numerical response variable A which depends on a categorical explanatory variable B. I also have another variable C that I'd like to check for confounding effects. So far I've been using ...
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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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4k views

Kruskal-Wallis test + Nemenyi post-hoc test: further multiple hypothesis correction needed?

I have used a Kruskal-Wallis test in a one-factorial design with samples that do not meet the assumptions for one-way ANOVA. To do this I have used the function ...
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1answer
702 views

Difference between samples in terms of frequency ranks

I have 3 different texts, and for each one of them, I have the frequencies of 25 letters appearing in those texts (Text A, letter A, freq = 5013; Text A, letter B, freq = 1462,...). These texts have ...
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1answer
656 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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645 views

Percentages from non binomial data: is ANOVA / Kruskal-Wallis appropriate?

I know ANOVA with percentages as already been discussed (Using ANOVA on percentages?) and (ANOVA-like test for bounded variables (percentages)), but the variables seemed different from my case. ...
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2k views

adjusting ties for kruskal.wallis

I would like to compare the means of three groups using the Kruskal Wallis test in R. My data looks like this: ...
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1answer
731 views

non equal variances alternative for kruskal wallis anova

I have a dataset with a total of about 6 groups set up, and there is a minimum of n=150-200 samples per group. Now when I look at the data, its not normally distributed, and the variances are not ...
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42 views

MANOVA: What to do with a u-shaped DV?

I am hoping to get some advice on my analysis for my MSc dissertation. I will try to keep it short but please let me know if there is more information I can provide to make the situation clearer. ...
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85 views

Should I use ANOVA or Kruskal Wallis?

I have 10 samples and 2 treatments. One of the treatments only has 1 samples in it and the distribution is not normal at all. This is my main concern because it violates the assumption that the ...
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1answer
488 views

Bootstrapping Kruskal-Wallis test of significance

I am working with a set of 6 variables collected at 4 time periods (I consider each time period as a class in the following). For each time period, I have 82 397 observations. If I plot the mean and ...
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203 views

Should I use one Friedman test or two Kruskal-Wallis tests on small sample?

I am looking at concentrations at 3 sites over 4 years, with 4 samples at each site. Because of the small number of samples, I believe I should use non-parametric statistical tests. My question is: ...
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73 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 ...
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1answer
1k views

Kruskall-Wallis test. How many degrees of freedom to report?

I have run a kruskall-wallis test to see if there is a significant difference in the amount of fish at each site. There are three sites (Site1, Site2 and Site3), with 80 observations of fish in each ...
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0answers
157 views

Kruskal-Wallis to compare different distributions - need to normalize due to different proportions?

I have a population of children with different genotypes, let's say genotype A, B and C. However, the proportions are different per group, for instance 60 children have genotype A, 50 genotype B and ...
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158 views

Choosing to adjust or not after Kruskal-Wallis rejection

I have a series of data (4 numerical variables) and 4 categorical variables (with multiple factors each). I need to test for differences between various subsets based on the categorical variables. ...
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1answer
69 views

Non parametric analysis

The my dataset is not normal distributed. In order to apply a non parametric analysis, exist only the Kruskal Wallis test or others? I need to find a test similar to ANOVA to apply a dataset not ...
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1answer
2k views

Three-ways Kruskal-Wallis test [closed]

I need to make a Kruskal Wallis a three ways. The my dataset is composed by x (Presence) and three variable. I want to see the statistical difference of my x versus all the factors. I try to apply the ...
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1answer
173 views

Why does power reduce when increasing the number of post-hoc comparisons?

I'm performing a Dunn's post test comparison of my data after a Kruskal-Wallis test (4 groups, treated and control each one has drug and vehicle injection). The comparisons I've been doing are <...