Frank Wilcoxon, chemist and statistician, best known for the Wilcoxon-Mann-Whitney (rank sum) test and the Wilcoxon signed-rank test, two widely used nonparametric rank-based tests.

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Hypothesis testing on SVM using parameters

1. Introduction I am working on a multi-class classification problem by using a ONE-VS-ALL classifier. I have no problem what so ever with the approach. I just wanted help in how can we interper ...
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24 views

How to Collapse Correlated Data for Wilcoxon Signed Rank Test and Sign Test Such that the Power Loss is Minimum?

Data Description: I am trying to evaluate my algorithm against 1 benchmark and 3 other algorithms (so, 5 total algorithms). I collected some data using the following procedure: I feed 10 iid ...
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10 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 ...
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64 views

Paired t-test vs Wilcoxon signed rank

I conducted a pilot study (n=14) which was evaluated retrospectively. I have four parameters with a pre-intervention and post-intervention score that I want to compare. I am wondering whether I can do ...
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1answer
15 views

Rules for Percentage of zeros in a zero inflated model

What percentage of zeros in the data should make us consider trying the sequence of models: Poisson -> Negative Binomial -> Zinf-Poisson -> Zinf-Negative Binomial, etc? I have two datasets with about ...
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41 views

Central Limit Theorem for Wilcoxon signed rank tests

Let $X_i, i=1,2,...,n$ be a set of iid observations, assumed symmetric about $\mu$. Let $R_i$ be the rank of the absolute deviations from some $\mu_0$, i.e. $R_i=\text{rank}(|X_i-\mu_0|)$. Let ...
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1answer
15 views

Problem with Wilcoxon test in SPSS

I have a question about Wilcoxon test in SPSS. For a work in my university i have to test 2 results of metrics applied in 2 algorithm (A2-NSGA3 and NSGA2), the results are as follows: ...
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1answer
27 views

Finding direction of inequality for two-tailed test

I'm comparing two sets of measurements using a paired difference test (specifically the Wilcoxon signed-rank test). I would like to find out whether there is a significant difference between these ...
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37 views

Hierarchical Wilcoxon signed-rank test?

I have a small number (<10) surveys given to a small number of respondents (<10) before and after a program of instruction. The survey responses are on a Likert scale, and the results of all ...
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1answer
10 views

Comparing Two Cohorts, Pre and Post scores

I'm working on a research project, and I could use a little assistance in picking the correct test. There are two cohorts that took a pre-test. Subsequently, the intervention group was given a ...
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25 views

Non-parametric repeated measures with replicates: Wilcoxon Rank Sum Test or Wilcoxon Signed Rank Test?

We want to assess the suitability of 2 devices A and B for performing a test task on a set of subjects. We use a quantitative measure to evaluate performance (i.e., time to complete the task). We are ...
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8 views

Should I rely on the result of Wilcoxon Signed rank or Kruskal Wallis?

I am writing a dissertation on the relationship between age but also investigating other factors such as income, and pro-environmental behaviour. If i test household income against 'Have you taken ...
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2answers
30 views

Positive average but negative z-value (Wilcoxon Signed rank test) [closed]

Can anyone explain why I get a negative z-value when I perform a Wilcoxon test but my average is positive?
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1answer
17 views

Wilcoxon Signed-Rank Test for one population

It seems that Wilcoxon Signed-Rank Test could be used not only for inference about the mean difference in a matched pairs, but can also be used for one sample setting. Now I have a dataset which is ...
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7 views

wilcoxon sum rank test steps when variables are measured in group

how to perform Wilcoxon sum rank test when one want to measure 3 variables and each variable data is to be collected from at least 6-7 questions. There are two sets of data of before and after ...
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20 views

Testing of pre-post differences for multiple conditions and non-normal distributed data

I have pre- and post-test behavioral data (response times) of 9 people (1 group). The task which people performed was divided into 5 sections which differed in the stimulus type. So I have variables: ...
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16 views

How can I control for a variable while conducting Wilcoxon Rank Sum Test?

I did a Wilcoxon rank sum test to figure out if there is any difference in the distribution of Variable X1 for two groups. The test results showed that the difference does exist. I, however, suspect ...
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2answers
28 views

How to apply Wilcoxon test to small sample with NAs?

I have the following data which show some values before and after a drug. I want to test whether the drug increased the mean. I think I should use Wilcoxon test, but I don't know what to do with ...
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1answer
117 views

How to choose between sign test and Wilcoxon signed-rank test?

I am trying to pick one from these two tests to analyze paired data. Does anyone know any rules of thumb about which one to pick in general?
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1answer
21 views

multiple comparison for discrete nonparametric distributions

I have N=24 controls and M=10 patients. (M can be 20 later) Each subject has one 3D image, each element of the image is a discrete value (integer) ranging from 0 to 4 [0,1,2,3,4]. It's like a score. ...
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20 views

calculating tabulated interval for Wilcoxon-Mann-Whitney rank sum test using R

I am following along with two tutorials on R-bloggers (both utilize the stats package). The first is for the Wilcoxon signed rank test (http://www.r-bloggers.com/wilcoxon-signed-rank-test/) and I am ...
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1answer
33 views

Unequal Sample Size and Wilcoxon Rank Sum Test

It is my understanding that it is okay to perform the Wilcoxon Rank Sum test with slightly unequal sample sizes. I just don't understand how the Wilcoxon accounts for the missing numbers in one group ...
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812 views

Have the reports of the death of the t-test been greatly exaggerated?

Reading through CV all-time classics I came across a statement that I would like to clarify. This is the post and my question refers to the closing remarks: "I have to note that all of the knowledge I ...
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45 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
39 views

multiple comparisons correction

Let's say I have the done the following biological experiment: I have 10 genetically different bacterial clones, which I have competed against a common reference clone (ancestral). I can then ...
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3answers
38 views

Can I both use T-test and non-parametric T-test for the same data?

For example, I want to do test on each variable independently. Some variables are normally distributed, some are log-normally distributed, some just can't be transform to normal distribution (not even ...
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1answer
29 views

Clarification on the Wilcoxon Signed Rank Test Procedure

The Wilcoxon Signed Rank Test is immensely intuitive and cool in its simplicity. So much so that any questions seem out of place. However,... I have found different procedures being detailed ...
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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 ...
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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 ...
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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. ...
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1answer
66 views

Cliff's Delta or Vargha-Delaney A?

We have two sets of non-paired numbers, and we wanted to know if they were different, and if so, how different they were. To that, we used Wilcoxon, which told us they were different (we got a ...
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2answers
39 views

Wilcoxon Rank-Sum: computing the exact $p$-value

I have two groups of data: $\{7, 9, 11\}$, $\{3, 8, 4\}$. I am performing Wilcoxon Rank-Sum on these data, based on the first group. Aggregated, we have $\{3, 4, 7, 8, 9, 11\}$. The test statistic is ...
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1answer
56 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 ...
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36 views

Testing for differences between two treatments with repeated measurements

I am a little uncertain which test / approach to take for the following problem. I am using R. Data I have data from an experiment. The experiment has two different treatments and I ran a total of 5 ...
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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 ...
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37 views

Test for very large sample

I have a cellphone income data. and i want to compare 2 groups. First group is the treated group, who got a promotion campaign. The second is a control group. I use Wilcoxon and Kolmogorov-Smirnov ...
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36 views

Should I use a contingency table or Wilcoxon Rank-Sum Test? (is chi squared nonparametric)

I have a debate over whether a contingency table or Wilcoxon Rank Sum Test (WRST) should be used in a particular situation. There are several problems with the contingency table, but I will mention ...
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What is the general relationship between L.S.A. CI and the exact CI in the sign test?

We know that we can use the large sample approximation in calculating the confident interval of the median(location) of the sample distribution in the Fisher's sign test. We can, at the same time, ...
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1answer
63 views

Wilcoxon signed-rank test for proportion variable response?

My response variable is a proportion. The explanatory variable is categorical with two levels which are not independent. The distribution of the response variable is different from normal. ...
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1answer
78 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 ...
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61 views

Why using the Wilcoxon Rank Sum Test instead of any other pairwise statistical test?

I am quite rookie in statistics and I have a simple question to ask. I have to compare pairwise 32 variables, each one with 10 f-measure outputs. I used the Tukey-HSD test and results were quite ...
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127 views

Why should we report Z when reporting the results of a Wilcoxon Signed Rank test?

I read these guidelines on how to report statistics in APA style and it recommends to report the Z score when reporting the results of a Wilcoxon Signed Rank test. Why is it important to report the Z ...
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33 views

Variance of Wilcoxon Rank-Sum Test (no ties)

$\newcommand{\E}[1]{\mathbb{E}\left[#1\right]} \newcommand{\r}[1]{r\left(#1\right)} \newcommand{\P}[1]{\mathbb{P}\left(#1\right)} \newcommand{\Var}[1]{\text{Var}\left[#1\right]}$ Given two sets of ...
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1answer
27 views

Wilcoxon Rank-Sum Test $H_1$ notation

This notation is from Nonparametric Statistical Inference, 5th ed., by Gibbons and Chakraborti. On p. 290, it states: Wilcoxon (1945) proposed a test where we accept the one-sided location ...
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52 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?
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106 views

Rank and z-transform instead of Wilcoxon?

Andrew Gelman in a recent post in his blog suggests using a rank, transforming the rank to a z-score, and then using parametric tests and tools instead of performing non-parametric tests. I never ...
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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") ?
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129 views

Wilcoxon Signed Rank Test reports “U” instead of “Z” in SPSS

Given two variables A and B with 35 random data points (generated with Excel in the range of 0 to 1), we applied Analyse -> Nonparametric Tests -> Legacy Dialogs -> 2 connected Samples in SPSS and ...
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8 views

Spearman correlation and ranksum test for 2-class problems

While Pearson correlation and 2-sample T test give the same p value and the correlation coefficient can be easily converted into t-value in 2-class problems, Spearman correlation and Wilcoxon ranksum ...
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173 views

Wilcoxon signed rank test for comparing classifiers

I am interested in comparing Classifier A with Classifier B. I have obtained Micro-Averaged F1 measures for Classifiers A and B that I intend to compare pairwise. I want to find out if Classifier A is ...