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.

learn more… | top users | synonyms

0
votes
0answers
35 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 ...
3
votes
1answer
28 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: ...
3
votes
1answer
55 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 ...
14
votes
5answers
333 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 using a Welch correction for unequal variances, or by a non-parametric test such as Wilcoxon paired signed rank test, the ...
0
votes
0answers
15 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 ...
0
votes
0answers
30 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 ...
1
vote
0answers
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 ...
1
vote
1answer
17 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 ...
1
vote
1answer
32 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 ...
0
votes
1answer
58 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 ...
4
votes
1answer
106 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 ...
2
votes
0answers
18 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
votes
1answer
33 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 ...
0
votes
0answers
30 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, ...
2
votes
0answers
21 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 ...
4
votes
2answers
240 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 ...
0
votes
1answer
43 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 ...
0
votes
4answers
56 views

Two groups are significantly different? Test to use

I have two groups of discrete data (integers): ...
0
votes
0answers
24 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 ...
1
vote
0answers
68 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.
1
vote
0answers
84 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 ...
1
vote
0answers
15 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 ...
0
votes
0answers
17 views

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
votes
1answer
113 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 ...
1
vote
2answers
62 views

How to test for significance if the variances are different?

If got data (value) of two types (cond true or false): ...
1
vote
1answer
52 views
1
vote
3answers
405 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 ...
0
votes
0answers
56 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: ...
0
votes
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 ...
1
vote
1answer
112 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
votes
1answer
162 views

Non parametric Wilcoxon Signed Rank test

I have the following data vector(in fact its 2392 data points long): ...
2
votes
1answer
113 views

Wilcoxon rank sum test methodology

I'm comparing the performance of two algorihtms $A$ and $B$ based on a metric. For each algorithm, I have $31$ independent samples that represent its performance. This samples are grouped in two ...
1
vote
1answer
253 views

Are pairwise Wilcoxon tests a valid non-parametric alternative to Tukey's HSD test?

I am trying to identify significant differences between groups from normal and non-normal distributions. When the distribution is normal the workflow is pretty straightforward: ANOVA and after that a ...
3
votes
1answer
53 views

Why do we assign fractional ranks in rank tests?

Both Mann-Whitney U test and Wilcoxon signed rank test follow this procedure: sort the data assign ranks, Ties receive a rank equal to the average of the ranks they span compute the statistic using ...
2
votes
1answer
20 views

Distribution heavily stacked on either limit - appropriate test?

I have two sets of results from an experiment that produces distributions with extremely heavily stacked sides and mostly uniform elsewhere. The aim of my analysis is to answer a the question roughly ...
2
votes
1answer
2k views

Difference between the Wilcoxon Rank Sum Test and the Wilcoxon Signed Rank Test using paired observations

I was wondering what the theoretical difference is between the Wilcoxon Rank-Sum Test and the Wilcoxon Signed-Rank Test using paired observations. I know that the Wilcoxon Rank-Sum Test allows for ...
4
votes
0answers
134 views

Bonferroni correction for two different tests on the same dataset

I am having trouble figuring out the correction factor to choose for a Bonferroni correction. Let me explain. I have two datasets, control ($x$) and data from left ($y_1$, affected limb) and right ...
1
vote
1answer
96 views

Adjustment of medians in the Siegel-Tukey test vs. the Wilcoxon test

I have two (unpaired) distributions. The distributions are far from being normal, so I'm using the Wilcoxon test to compare their medians: the Wilcoxon test does not reject the null-hypothesis ...
0
votes
1answer
58 views

Wilcoxon test to support logistic regression

I want to test the hypothesis that IV 2 (post-test value) is a better predictor for the criteria (no success vs. success) than IV 1 (pre-test value). Those IVs are indicators for static vs. dynamic ...
0
votes
1answer
41 views

what kind of non-parametric test to use?

I collected data on one sample, the DV could be separated into two groups (success yes vs. no) and then I have several IVs with interval scale. I just don't know if to use Wilcoxon or Man-Whitney ...
2
votes
2answers
225 views

Skewness adjusted t-stat

I've some data that is divided into a series of groups and am testing whether the mean is different from 1. The data is highly skewed, with skewness ranging from 1.10 to 26! I did a one-sample t-test ...
1
vote
0answers
20 views

Measuring treatment effect on top-ranked subjects selected at point in time from longitudinal data

I am trying to measure the effect of treatment after some time on a group of subjects who were selected for treatment because they were the highest (top 1200) ranked subjects during a single period ...
6
votes
1answer
133 views

Use of Wilcoxon test for non-normal data akin to Two One Sided T-test

I'm analysing paired data for equivalency and it's not normally distributed, i.e., the difference of the paired result is not normally distributed due to, amongst other things, outliers. If it were ...
0
votes
2answers
89 views

Testing which groups have had a significant change

I have three groups with two hundred individuals each, and each individual within a group has a pre and post treatment measurement. A single group contains individuals with similar pre measurement ...
0
votes
1answer
326 views

Applying a post hoc Wilcoxon signed rank test to a Friedman when there are different sample sizes

I conducted a Friedman test to related-sample group in three conditions (pre-treatment, post-treatment and 6-month post treatment). Out of 216 participants that completed the first two stages, 50 of ...
1
vote
0answers
47 views

List of sample arrangements at a given Wilcoxon / Mann-Whitney test statistic

Consider a Wilcoxon-Mann-Whitney test statistic, either in the form (i) "W = sum of ranks in sample A"; or in the form (ii) "sum of ranks in sample A - the minimum possible sum of ranks in sample ...
4
votes
2answers
490 views

Is the W statistic outputted by wilcox.test() in R the same as the U statistic?

I've recently been reading about the Mann-Whitney U test. It turns out that to carry out this test in R you actually need to run a Wilcoxon test! My question: is the W statistic outputted by ...
2
votes
1answer
180 views

Can I use Wilcoxon Signed-Rank Test to test pairs of data in a time series?

I have a dataset of measurements (non-normally distributed). Each line of this dataset is composed by two measurements of the same variable in a specific time (i.e. XYY [time, meas1, meas2]). This ...
1
vote
1answer
515 views

Wilcoxon one-tailed test

It's regarding a one-tailed Wilcoxon sign test. I am comparing (fictional) ratings of liking before and after a woman shaves off the hair. The design is complicated. I will do my best to explain. ...
0
votes
2answers
449 views

Should I expect a Z-Score as an output from a Signed Rank test?

I have some data that is highly skewed. I want to test whether the median of the data is different from 1, so I decided to use a Wilcoxon Signed Rank test. The description and implementation of this ...