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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54 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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30 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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28 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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5 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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98 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 ...
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35 views

Correlation between two samples of different size

I have all price quotes from a stock (to be more precisely CSAN3 from Ibovespa Exchange - Brazil) from 2010 to 2015. I was asked to get the correlation from the log returns year-by-year. This is ...
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1answer
29 views

How to compare versions of treatments

I want to compare three different treatments, in my case lamps. Every lamp has a clear and a matte version, so there is a total of six. I have deployed them for a number of nights and attracted ...
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17 views

Which test for paired data with small sample size?

I have four paired samples (subjects tested once, then again under different conditions), and am unsure which test to use to calculate significance with such a small sample size. It was suggested to ...
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10 views

Testing if two rankings are equivalent

I have some process A that assigns values y_i for i=1:N to instances x_i. ...
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108 views

How to do hypothesis testing in this case?

A new methodology has been proposed for teaching English to undergraduate students. This methodology (which we call X) has been tested with a group of 27 students. Initially, the lecturer in charge of ...
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28 views

Computing Test Statistics when Measurements have Error

Edited to better represent sources of measurement error I have 2 groups of subjects(say male and female centipedes) that I made measurements on(Average length of the subject's leg). The measurements ...
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1answer
72 views

KS Test and Wilcoxon Rank Sum Test, large differences in p values

I am relatively new to non-parametric tests. I wrote the following R code to test 2 sample tests using the KS test and the Wilcoxon Rank Sum test. Drawing 2 samples of various sizes from unit Normal ...
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1answer
42 views

For a longitudinal observational study, what is the best method of comparing cost before and after intervention?

I have a sample of 200 patients, with data for 2 years. During year 1 they are on treatment A and accumulate overall healthcare costs of X. During year 2 they are on treatment B and accumulate ...
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46 views

Why exactly is normality an assumption in a T-test but not a Wilcox rank sum/Mann Whitney U test when obtaining a p-value?

In addition to the question, please do correct anything below that I have incorrect. I understand how the test statistics for a t-test and WRS/MWU test are calculated. In a t-test, $t=\frac{\bar ...
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2answers
52 views

Appropriate visualization for the Wilcoxon signed rank test

I have question regarding the Wilcoxon test and if the results can be represented visually. I had 10 participants in my experiment where by I asked participants to read sentences and then they ...
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1answer
35 views

Choosing between and properly interpreting Analysis of Variance vs Wilcoxon rank sum test

(Newb on this, so please assume good faith but low skill) I have this set of data where I'm interested in whether there is a significant and meaningful difference in ...
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1answer
40 views

Is this an appropriate use of the Wilcoxon signed rank test

Please see data table: ...
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2answers
45 views

ttest or wilcoxon

for a user study I want to compare some tasks. Each tasks has 2 conditions on a intervall scale. From each task I want to test the the conditions with: a t-test if both samples are on a normal ...
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28 views

Test statistics in IR (t-test vs Wilcoxon vs signed test)

I have just read this paper about different test statistics one could use in Information Retrieval (IR), discussing whether Wilcoxon, Sign-test or Student t-test would be more reliable for comparing ...
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29 views

Using standard error or standard deviation bars in within-subject design: How should i interpret and report this?

I have gathered results from a study that tests participants reaction time in a task that tests two conditions simultaneously by randomizing the trials within the experiment. I have used a wilcoxon ...
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14 views

What are pro-cons of Wilcoxon signed ranks when compared to sign-test on information retrieval

I have to judge whether a search engine A retrieves better results than B. I have the average precision of each for 10 different queries. I run both sign-test and Wilcoxon signed-tanks test. Now, the ...
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65 views

Wilcoxon signed rank test - Normalize data or not?

I am comparing my algorithm's performance with other algorithms, for a minimization problem. There are ten different benchmark problems, for which I have computed the average solution quality for all ...
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2answers
89 views

Algorithm and R code for dealing with ties in Wilcoxon rank-sum test

1) I think one of the algorithms used to handle ties for the Wilcoxon rank-sum test (a.k.a. Mann-Whitney U test) is Streitberg / Rohmel. I could not find a good source which explains the algorithm/ ...
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76 views

Using Friedman Test or Wilcoxon Signed-Rank Test to compare two sets of Likert data

I distributed a questionnaire consisting two different sets of Likert statements. In the first section, I asked the respondents to rank some employee attributes (on 5–point Likert scale, 1 not ...
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17 views

Permuted block design Wilcoxon sum rank test

I need to do a Wilcoxon rank sum statistic for some data with a permuted-block with 2 blocks of size 6. However, I'm confused how we deal with the permuted-block randomization. My book says When ...
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34 views

Bonferroni adjustment according to which families?

We have 17 subjects in a crossover design of three groups: Challenge agent (CA) CA+ compound of interest (CI) CI - Our data proves this has no physiological effect, and is thus not used in ...
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20 views

Wilcoxon V Statistic or W Statistic - interchangeable?

I have seen reference to the W, V and T statistics all within the Wilcoxon Signed rank Test, and this has me confused. First question: Are these used interchangeably? My test is the Wilcoxon Signed ...
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11 views

paired subject design test of proportions

I am analyzing a performance data set and would like to compare across two different conditions. I have three subjects, which were tested over a number of trials. Each trial had a chance of being in ...
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1answer
71 views

What is not normal distribution?

I am running analyses for my dissertation and just got myself in a muddle. I am running descriptive stats to determine whether to use paired t-tests vs Wilcoxon signed rank tests. I've read that it ...
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1answer
91 views

How can a paired test less powerful than unpaired test?

I'm using wilcox.test to compare two timepoints as such: a <- c(1,2,3,4,5) b <- c(2,3,4,5,6) wilcox.test(a, b) The ...
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25 views

Wilcoxon Signed Rank test in R gives me a very small p-value even though the difference is very small [duplicate]

I have a dataset with 499 observations on the intake of betacarotene. I have data on the dietary intake as well as the total intake (including dietary supplements) on the same 499 persons. I want to ...
2
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1answer
71 views

Help with understanding the assumptions of Wilcoxon signed rank test

I am comparing the monthly losses for actual and forecast losses for the same time period to see if our forecasts are in line with actuals. This is for a 12 month period. I am bit confused about the ...
3
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1answer
44 views

Determine if there is a difference between two large vectors of different sizes of non-normal quantiative data in R

I have two vectors that are of unequal sizes. They contain quantitative data that does not form a normal distribution. I would like to see whether or not they are statistically different. Is there a ...
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1answer
91 views

Critical value for Wilcoxon one-sample signed-rank test in R

I am trying to find the critical value for the Wilcoxon one-sample signed-rank test. Currently, I can find the value using tables. I looked at qwilcox() in R, but ...
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2answers
167 views

Mann-Whitney U test and paired data

I've read that working with paired data requires other method than Mann-Whitney $U$ test. I am not sure about how formally accurate is this statement. Reasons: Suppose that there is a set of $n$ ...
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166 views

Is the Wilcoxon test the right test to see if total donations differ?

Background: My software asks users for optional donations of any amount. I split test donation requests among users to find the best way to ask: 50% get request version 1, 50% get request version 2, ...
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27 views

Other statistical tests for paired data

Are there other statistical tests available to compare paired sets of data e.g. {1, 2, 2, 3, 4} v's {3, 3, 3, 2, 5} for similarity, aside from the paired Wilcoxon and paired Student t-test?
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60 views

Confidence intervals for median from Wilcoxon signed rank statistic

We are given the sample $X_1, ..., X_n$ from a common distribution with median $\mu$. Using Wilcoxon's signed rank statistic, how can I construct a confidence interval in terms of the order statistics ...
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50 views

wilcoxon rank test negative z

my research is basically to see the effectiveness of certain symbols presence in advertisement towards the attitude using likert 1 until 5 , Since my respondents is less then 30 due the tight control ...
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1k views

Effect size to Wilcoxon signed rank test?

Some authors (e.g. Pallant, 2007, p. 225; see image below) suggest to calculate the effect size for a Wilcoxon signed rank test by dividing the test statistic by the square root of the number of ...
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1answer
88 views

What is the proper abbreviation for the test statistic in Wilcoxon signed rank test? [closed]

What is the APA conforming symbol for the test statistic from the Wilcoxon signed rank test? Different statistics software outputs all kinds of letters from V to Z. I thought it was W?
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27 views

Do I need to use weighted means with the Wilcoxon signed rank test?

I have 22 patients. They have been measured pre and post treatment. There are 3 measurements per patient before treatment (pre baseline), and four measurements after treatment (post baseline). There ...
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3answers
421 views

Why is the asymptotic relative efficiency of the Wilcoxon test $3/\pi$ compared to Student's t-test for normally distributed data?

It is well-known that the asymptotic relative efficiency (ARE) of the Wilcoxon signed rank test is $\frac{3}{\pi} \approx 0.955$ compared to Student's t-test, if the data are drawn from a normally ...
3
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1answer
130 views

Is Wilcoxon Signed-Rank Test the right test to use?

I have a dataset of the following form: ...
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89 views

Significant Friedman's Test, but non-significant post-hocs?

I have a sample of 25 in my within-subjects design, with my DV as error rates. The data contains a lot of zeros (i.e. no errors) and is highly negatively skewed, so I can't run the repeated-measure ...
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104 views

Bootstrapped BCa confidence interval of median (R package simpleboot) does not correspond with Wilcox.test p value

I am using R to compare the medians of two groups. Each individual has received a score of between 0 and 100. Both distributions are very skewed. The median of group A (n=33) is 87.8 (IQR 75.1, 100.0) ...
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2answers
104 views

Chisquared on categorical data or a Wilcoxon test on the counts hereof?

This question is related to a question I had in R on SO here The background of my question is fairly simple. I was given two "databases" in the form of data.frames ...
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2answers
92 views

Wilcox.test in R

I have tried to identify differential expressed genes between two sets of Microarray samples by running wilcox.test for each gene, but the p-values of most of the ...
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68 views

Pairwise Wilcoxon test gives wrong results

I'm trying to perform a pairwise Wilcoxon test in R. When using Bonferroni p-adjustment I got only 1's and 0's. When changing p-adj to 'none', I get this: ...
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1answer
68 views

Comparing medians from two groups

Hi: I have a survey where respondents were asked to rank a series of statements in terms of how much they agreed with them. There were seven statements. So, for each of seven statements, each ...