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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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
25 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
57 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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2answers
143 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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21 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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23 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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17 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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103 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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42 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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23 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
222 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
64 views

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

I have a dataset of the following form: ...
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39 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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64 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) ...
2
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1answer
78 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
69 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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0answers
28 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
50 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
36 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
73 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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6answers
767 views

A principled method for choosing between t-test or non-parametric e.g. Wilcoxon in small samples

Certain hypothesis tests can be approached using Student's t-test, possibly with a Welch correction for unequal variances in the two-sample case, or by a non-parametric test such as Wilcoxon paired ...
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19 views

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 ...
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1answer
47 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
24 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
37 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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1answer
92 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
97 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 ...
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1answer
123 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 ...
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20 views

Test for pairs of small integers

I have two classifiers, say $A$ and $B$ and I am performing 10$\times$10-fold cross-validation on them and record the number of instances correctly classified from the test set. Unfortunately, the ...
2
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1answer
35 views

wilcox.test usage in R

I would like to know if there is a difference in the values taken from measurements of a given characteristic sampled at primary forest (Point=1) and secondary ...
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0answers
36 views

Confused about the proper way of testing for an improvement or worsening

I want to check if a new equipment improves a score compared with the older equipment. My database contains the score with the old equipment, and the scores with each new equipment. I googled, ...
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0answers
27 views

Rank Order Analysis with Missing Values

I have several survey questions that allow a respondent to choose their top three choices from a set of potential answers--basically "What is the most important, 2nd most important, 3rd most ...
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359 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 ...
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1answer
48 views

Wilcoxon tests in Doronix Math Toolbox

I'm using Doronix Math Toolbox. They have statistical functions (http://www.doronix.com/statistics.html). I can't figure out how they are finding p-value in ranksum and signsum tests. Does anyone know ...
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4answers
75 views

Two groups are significantly different? Test to use

I have two groups of discrete data (integers): ...
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0answers
25 views

Wilcoxon Signed Rank when subjects appear in each sample n times.

I have sales data and would like to see if the median sales for an employee has increased as a result of this training. Thus, I have pre and post data, since it is only six months and am interested in ...
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96 views

Wilcoxon matched pair signed rank test after using CEM

Can I run a Wilcoxon matched pair signed rank test after using Coarsened Exact Matching to match data? If yes, please guide me through the process. I use STATA.
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112 views

Can I use wilcoxon signed rank test for time series data

I have a question about wilcoxon signed rank test. I have 2 different speed profiles (speed starts from time 0 to 100 sec) of the same participant that was given 2 different treatment. I would like to ...
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17 views

Comparing patient proportions between one ER and the national average

I am looking to compare the proportion of emergency room attendances by hour of the day against a national average proportion (plus some other tests for ER variables such as referral methods and ...
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0answers
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testing for differences in means after an experimental change

I have a set of Mechanical Turk-like workers who have been paid $0.25 per task to complete tasks from a finite, but very large, pool of tasks, and I have data on how many tasks they've completed and ...
0
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1answer
168 views

Performance Evaluation for multiple classifiers in machine learning with Wilcoxon Rank Sum Test

I use four feature descriptors for five independent runs with each run randomly selecting the training set and testing set from the total labeled samples. SVM is the classifier. After acquiring the ...
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2answers
121 views

Correct approach using t-test and Wilcoxon rank sum test?

I want to compare 2 datasets. I have a biological structure A with its atom coordinates which are a few thousands. I also have from these atom coordinates the coordinates over time of about 20 ...
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2answers
74 views

How to test for significance if the variances are different?

If got data (value) of two types (cond true or false): ...
2
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1answer
75 views
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3answers
785 views

Testing if two non-normal distributions are significantly different (K-S or Wilcoxon or both?)

The Big Question I'm trying to decide between K-S and Wilcoxon (or something I haven't thought of yet) for two data sets I want to prove are significantly/insignificantly different from one another ...
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66 views

analysis of non-normal data

I collected some data on a species of goose called Brent Goose over the winter. A csv file of the data can be downloaded from Dropbox or imported straight into R with this code: ...
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0answers
25 views

How to interpret results from a nonparametric Wilcoxon test [duplicate]

I did a research study that looked at pre and post test scores from a test. I was asked to run a Wilcoxon test, which I did and now I need to know how to interpret the test results but also how to ...
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1answer
270 views

Paired or unpaired Wilcoxon test?

I counted the number of geese on an intertidal mudflat on 100+ days over the winter. I made two counts on each of these days: one at low tide and one at high tide. I want to know if the number of ...
2
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1answer
179 views

Non parametric Wilcoxon Signed Rank test

I have the following data vector(in fact its 2392 data points long): ...