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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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 ...
4
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1answer
35 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
40 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
23 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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6 views

how to find critical values of Wilcoxon signed rank test in R [migrated]

I just can't find it anywhere. I know there's a qwilcox() function, but for some reason it only shows critical values of Mann-Whitney for me. Here's the table of ...
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34 views

Is this an appropriate use of the Wilcoxon signed rank test

Please see data table: ...
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41 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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20 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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19 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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9 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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44 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
57 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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49 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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16 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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0answers
23 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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0answers
17 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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9 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
62 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
80 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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16 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 ...
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1answer
56 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 ...
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1answer
32 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
72 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
119 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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160 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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24 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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38 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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38 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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687 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
70 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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25 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
335 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 ...
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1answer
100 views

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

I have a dataset of the following form: ...
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70 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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93 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
101 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
82 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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61 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
62 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 ...
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1answer
44 views

Two Sample Wilcoxon Test with Different Sample Populations

We were given an example the other day for Wilcoxon test with two samples with different populations ($No. untreated=n_1=4$ and $ No. treated=n_2=7$). It was stated that: ...
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1answer
84 views

Why are there two forms for the Mann-Whitney U test statistic?

I have encountered two forms for calculating the two-sample Mann-Whitney U test statistic, which are: $$U_1 = R_1 - \frac{n_1(n_1 + 1)}{2}$$ and $$U_1 = n_1n_2 + \frac{n_1(n_1+1)}{2} - R_1$$ where ...
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How to choose between t-test or non-parametric test e.g. Wilcoxon in small samples

Certain hypotheses can be tested using Student's t-test (maybe using Welch's correction for unequal variances in the two-sample case), or by a non-parametric test like the Wilcoxon paired signed rank ...
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When compare a variable in different times, one has normal distribution, another doesn't, which test should I use?

The question is to compare means of sales volume in different periods. So I got sales period 1 and sales period 2. Sample size is 40. The skewness, kurtosis, test of normality and histogram all show ...
2
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1answer
57 views

non-parametric tests with significant difference in sample sizes

I have outcomes from a biological expt., where we have measured DNA lengths that has been affected. For condition1, I have 11 observations (length of DNA) and for condition2 I have approx. 116000. I ...
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27 views

Is Wilcoxon test still valid if there is some shared information?

I have $N$ samples from a population, and to each sample I apply both method A and method B, recording the time each takes to run ($T_A$ and $T_B$, say) I then define a new pseudo-measurement for ...
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1answer
26 views

Exploring Diffrences and Agreement with Wilcoxon and Kendall - both tests show significant findings

I calculated a Wilcoxon Signed Rank Test to investigate differences between a pair of dependend variables. Also I conducted a Kendall's tau-b on the same variables. Surprisingly both tests get ...
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1answer
40 views

Comparing ranks within groups

I've got data from a psychology research study where participants are given scores for various different situations. I'm looking at comparing the rank of those scores - is the person ranked as 1st in ...
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125 views

Appropriate non-parametric post-hoc test for baseline comparisons?

I want to evaluate several "classifiers" (machine-learning algorithms) with paired samples. I do not want to compare each algorithms' performance to every other (n x m comparison) but only compare the ...
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2answers
135 views

Mann-Whitney/Wilcoxon rank sum test in R with a table of tallies

I have a 10 treatments, 5 samples per treatment, and the result of each treatment is ranked on a ordinal scale: Poor, Fair, Moderate, Good, Excellent. I have the data tallied up so I have the total ...
4
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1answer
161 views

Wilcoxon rank-sum test for multivariate case when pdf is known

I have sample of around 100 of observations. Each of them is the vector of real numbers of size 30. Also I have pdf which I think may describe the source distribution of my sample. The pdf has ...