Questions tagged [fishers-exact]

A hypothesis test for contingency tables.

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Can exact tests compare groups from case-cohort studies?

I have reviewed several helpful threads most related to my question and many thanks to the authors. The first thread suggests odds ratio is valid for cohort studies, but risk ratios or hazard ratios ...
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Statistical test to show if there is a difference between A and B (count data)

I conducted 20 tests (in parallel) where there was a choice between A and B and after a defined period of time, I counted the number of individuals that chose A or B (count for A and B is always ...
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Comparing responses between groups and conditions

I have a group of subjects that were tested under 2 visual stimuli. Each stimuli was presented in 2 directions (the stimulus is a flow of objects, once left to right and then right to left). And the ...
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How can I do fishers exact test if only frequency is available not the count?

I want to compare two allele frequencies from two populations. I use Fisher's exact test for this. But I don't have the actual count of the alleles but just frequency. For eg: Frequency of Population(...
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Confirm that an eventual over-representation in a sample is statistical significant

I need opinions on this one, so any thought you can contribute will be highly appreciated. My population is an entire set of customers, my sample is all the customers to whom something specific, which ...
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Testing the difference in sensitivities between two lab tests - with part overlapping populations

I have two rapid diagnostic tests for which I test their sensitivity (+/-) in detecting cases against the gold standard (ELISA, also +/-). I now want to test whether the tests perform significantly ...
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comparing proportions in two potentially non-mutually exclusive populations when one population=100%

A system I've been working with can be modeled as a number of lamps with two light bulbs, one green and one red.  Going into the project I thought each lamp could have three states: both lights on, ...
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Sample size calculation in COVID-19 study

From A Randomized Trial of Hydroxychloroquine as Postexposure Prophylaxis for Covid-19 by Boulware et al. in the New England Journal of Medicine (https://www.nejm.org/doi/full/10.1056/NEJMoa2016638), ...
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In which situations should do I perform a Fisher test?

I have the species richness (number of species) of different habitats. ...
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Fisher exact test with confounding variable

I'm using a Fisher exact test to understand whether a Webpage-A is more likely to induce conversion compared to another Webpage-B. ...
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Reference for Fisher's exact test for $r \times c$ tables?

I see that in R, there is an example of running Fisher's exact test (see ?fisher.test) with an $r \times c$ contingency table with $r, c > 2$. I could not find ...
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Likert scale vs Dichotomous. Please suggest

As per my understanding dichotomous response (Agree vs Disagree) has much better Power than Likert scale, because it is possible to do Fisher's exact test on 2-way contingency table, while such tests ...
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Alternative to Fisher's exact test with swapped H1 and H0

Is there an alternative to the Fishers's exact test that has as null hypothesis that the relative proportions of one variable are dependent of the second variable?
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Chi-Square Versus Fisher's Test Versus Welch T-Test

I am having a hard time to understanding when to use which of these tests. Fisher's test is useful for small sample sizes to compare categorical variables. Ok. Take a simple example, you have data ...
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Post hoc for Fisher's exact test with a 2x6 contingency table

I am looking to see if and how tree height differs between areas of undisturbed and historically logged forests. Height was estimated in meters but categorically (1-6, 6-11, 11-16, 16-21, 21-26, 26-31)...
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What is ncp of negative hypergeometric distribution?

https://github.com/SurajGupta/r-source/blob/master/src/library/stats/R/fisher.test.R#L127 I see non-centrality parameter ncp on the above page. But I don't find ...
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Multiple comparisons and non-independent tests in prevalence data

Thanks in advance for all and any help. I have tested six different species for a disease on both an island and a mainland region. I wish to compare the prevalence of the disease between the island ...
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Check if multiple percentage are significant

I have 3 measurements of a very skew distribution, depending on three different technique. In general, I can do thousands of test and the result is either "fail" or "success", being the "fail" far ...
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Fisher's test for a $2 \times 2$ table within a $2\times k$ table

I'm struggling with analysing the following categorical data shown in the barplot. There are 5 categories (R, D, E, N, A) and I have the number of votes (number of respondents) for each one. As shown ...
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Computing significance of overlap between two sets in Python

I am computing the significance of an overlap between two subgroups, each in two related datasets 1 and 2. For instance: Dataset1 total: 500 Dataset1 subgroup: 100 Dataset2 total: 300 Dataset2 ...
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Distribution of p-values in Fisher Exact Test when second column is rare

This is a simplified version of the problem (which actually has 3 columns instead of 2, and takes account of direction of influence): Suppose we have alleles G and a trait T. We're interested in ...
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Statistical test to detect regional excess of observations compared to background observations

I have data on the protein position of genetic variants. I want to determine whether there is a region of the proteins with a significant excess of variants relative to controls. Consider this ...
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How Close Should Rows of Contingency Table be to Trigger p-value = 1?

I've been running some simulations on genotype effects on phenotypes. I'm representing genotypes by 0, 1 or 2 (the number of copies of the minor allele) and phenotypes as 0 or 1. Thus my contingency ...
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Alternative test

I am doing a peer review. The article is about the effect of yokukansan (YKS) on behavioral and psychological symptoms of Alzheimer disease. There were 15 patients, divided into 2 groups: the ...
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Fisher.test alternative problem in R

I found a weird thing about the "alternative" argument in fisher.test in R ...
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R: Same dataset, different units and then, chi-square test no longer works

I am a beginner in R and statistics. I conducted Chi-square test to see if there is a significant difference/relationship between two distributions. Then, I changed my units to percentage over ...
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Fisher's exact vs chi-squared [duplicate]

I'm quite new to statistics. Recently I've been struggling with the difference between a chi-squared test and Fisher's exact test. Compared to chi-squared test, why does a Fisher's exact test depend ...
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Compare two non-mutually exclusive distributions

I try to compare two distributions for significant differences. One set is the number of species per animal group while the other set is the number of publications per animal group. The data looks ...
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What Statistical Analysis test do I run for Pre/post test?

Hello I am conducting a study where I examine patients who have not received a flu vaccination. In all I have 45 participants all who have not received the vaccine. I implemented and educational ...
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Why does Fisher’s exact test use the hyper geometric distribution rather than the multi nomial distribution?

To understand hypergeometric and multinomial better, I’d like to know why fisher exact test used hypergeometric rather than multinomial distribution.
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Fisher's exact test vs chi-squared test

I have read some books in which Fisher's exact test will provide an exact p-value, but the assumptions underlying experimental design are not routinely met in practice. Apparently Fisher's "lady ...
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Sample size in Fisher's exact test with larger contingency tables

I'm using Fisher's tests to evaluate contingency tables that are larger than 2x2; because they relate to transitions between behavioural states, they are usually 8x8, 9x9, sizes like that. I am ...
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How to analyse a contingency table with specific expected distribution?

I have a 2x2 table of single nucleotide substitutions in DNA. The data rows represent the nucleotides in one genome (A) and columns are the nucleotides in the same positions of a different genome (B). ...
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How to Test Sampling Methods

Suppose I have a population, $P$, of 100 individuals and I am devising 3 algorithmic methods to sample 20 people from said population: $A$, $B$, and $C$. We know that $C$ is a random, unbiased ...
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Assumptions for Univariate Analysis

I am working a binary classification problem. To identify the risk factors, I would first like to do univariate analysis and then do ...
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Chi-square of Fisher exact test for large samples

The usual argument behind choosing chi-square or Fisher exact 2x2 test is that the Fisher exact test answers exactly a wrong question, while chi-square test answers approximately a right question. E.g....
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Fishers Exact Test for Dependant Sample in RStuido

I have a small dataset with a group of members which were exposed to a treatment and then again, their purchasing behavior was measured. Please note that there is no control group here, it is a case ...
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Examples for exact tests which are not permutation tests

Wikipedia states (without citation): Sometimes permutation test is used as a synonym for exact test, but although all permutation tests are exact tests, not all exact tests are permutation tests. ...
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What does the assumption of the Fisher test that “The row and column totals should be fixed” mean?

As this source states, one of the assumptions to perform Fisher's exact test of independence is that the row and column totals should be fixed. However, I find the explanation coming with it pretty ...
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Compare frequencies for nominal values between two groups

I collected two sets of usability problems during a user study and an inspection done by experts. Each problem was assigned to a category. I want to find out if there are significant differences in ...
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Manual computation for Fishers exact test for tables larger than 2 x 2 [duplicate]

I am wondering how to perform a Fishers exact test on my data which contains two columns and three rows. One of the cells contains zero. ...
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Examine significance of the effect of an attribute on the effect of another attribute

I'd like to examine the effect of an attribute on the effect of another attribute on certain behaviour. To explain what I mean: I tested two groups of 110 people on whether they did x. One of the ...
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How to do power analysis for Fisher exact test in tables larger than 2x2? [duplicate]

I have 4x2 contingency tables and would like to perform Fisher's exact test on them. R stats package(https://www.rdocumentation.org/packages/stats/versions/3.6.1/topics/fisher.test) supports 4x2 test ...
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How to conduct a test for independence in case of skewed classes (experiment design)?

The setting is as follows. We have a population of size $N$. Each subject has two properties $A$ and $B$, which can be either true or false. The question is: if for a random subject $A$ holds, is the ...
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Research participants maknig simultaneous choice: is it between or within subject design?

This question is about terminology. Assume the following scenario. A research participant is asked to choose one out of four options: products A and B in packagings X and Y. That is, the choice (...
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Compare specific recovery with random expectation

i am reading a scientific article and i would like to understand how a specific statistical calculation is done. I am missing the principle and the method. If somebody could be so gentle to explain me ...
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why is the margin (total number of sample) important when deciding between hypergeometric and Fisher's exact test

My impression is that both of hypergeometric and Fisher's exact test are similar in calculating the significance of contingency table. The main difference is whether or not you know the margin (if you ...
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Testing for Proportions (Fishers Exact Test vs BS T-Test)

If I want to test whether two proportions (from two independent samples) are significantly different, is there any advantage of using the Bootstrapped T-Test over Fishers Exact Test? It seems as ...
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Different formulas for two-sided mid $p$-value ($2\times2$ table setting)

I'm interested in testing independence of two binary variables in a $2\times 2$ table: i.e. $H_0: \theta=1$ against the two-sided alternative $H_1:\theta\neq 1$, where $\theta$ is the odds-ratio. ...
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Interpreting a very small odds ratio when the Fisher's exact test is significant

I'm having a hard time interpreting odds ratios (OR) for a 2x2 contingency table. ...

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