Questions tagged [fishers-exact-test]

A hypothesis test for contingency tables.

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1answer
74 views

Does it have any meaning to compute the $\chi^2$ and the exact Fisher test on big contingency tables

I have several datasets containing integers. I want to perform a bivariate analysis between a specific subset of variables. However, some of them have a lot of modalities. Is computing a $\chi^2$ ...
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1answer
54 views

How to deal with zero cells in 2 x 2 tables, using R

I am trying to look at the relationship between two nominal variables, using R. However, I am not certain how to deal with cases where a 2 x 2 contingency table has one or more zero cells, as shown ...
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0answers
38 views

On power of solving Lady Tasting Tea?

I've learned that the solution for the lady tasting tea experiment is the Fisher's exact test. Is it the most powerful test for solving this problem? If there are other tests, how do they compare in ...
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329 views

Interpretation of Fisher's exact test confidence interval [duplicate]

I am having difficulties with the interpretation of Fisher's exact test confidence interval. I have a contingency table with some numbers below: I perform Fisher's exact test: ...
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39 views

What statistical test should be used to compare groups when the assumption of independence is violated?

I would like to test if there are statistically significant differences between three groups (defined by an outcome measurement) for some categorical and continous variables, respectively. Normality ...
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0answers
18 views

How can I separate the abundance factor of the incidence results?

I must calculate the incidence values for Watermelon Mosaic Virus in different seasons within of habitat. This incidence data comes from infection detection of some plant sampled in different habitats ...
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22 views

Calculate group with highest defective rate

I have data on several types of machines, each with a different rate of failure. I have samples of failures/non-failures for each machine type. The samples are small relative to the population range ...
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1answer
170 views

Two sample test of independent proportions with weighted data?

In analysis of survey data, response data may often be weighted to reflect the sampling procedure or relative importance of the respondents. For instance, a consumer survey may sample 50 respondents ...
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810 views

Fisher's exact test (one-sided, greater) gives p-value = 1

I have a contingency table that looks like this ...
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138 views

What is the value of an infinite odds ratios with non-signification p-value?

I have a contingency table as follows: Tumour Healthy Pos Neg Pos 4 0 Neg 2 3 I ran Fisher's exact test to get the odds ratio (using R) and ...
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1answer
76 views

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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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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1answer
35 views

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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4answers
391 views

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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1answer
53 views

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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1answer
383 views

How to do a fisher's exact test for 5x2 table with 0 values?

I want to do a 5x2 contingency table Fisher's exact test, but I have some zero values. How do I do this? What is the simplest way to do it? I have access to SPSS but I know very little about the ...
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1answer
145 views

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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1answer
63 views

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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34 views

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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143 views

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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1answer
498 views

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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1answer
13 views

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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1answer
82 views

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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1answer
231 views

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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1answer
49 views

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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1answer
30 views

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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1answer
249 views

Fisher.test alternative problem in R

I found a weird thing about the "alternative" argument in fisher.test in R ...
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1answer
31 views

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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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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1answer
81 views

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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128 views

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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77 views

the difference between GLM and fisher's exact test

I want to compare the enrichment or overlapping between 2 lists. I found some paper use fisher's exact test, or other papers use GLM (logistic regression). Does anyone know what the difference ...
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1answer
35 views

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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1answer
26 views

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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154 views

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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64 views

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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1answer
47 views

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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1answer
65 views

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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1answer
1k views

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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1answer
286 views

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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1answer
64 views

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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0answers
43 views

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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1answer
21 views

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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1answer
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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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1answer
9 views

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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0answers
15 views

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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0answers
90 views

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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1answer
121 views

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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