# Questions tagged [fishers-exact]

A hypothesis test for contingency tables.

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21 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). ...
24 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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### 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 ...
21 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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### 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 ...
44 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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### 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. ...
39 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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### 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 ...
22 views

### 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. ...
94 views

### ANOVA or Fisher's Exact?

I need to compare (check for any statistical significance) eight groups (categorical data: group A-H) for which I have only the frequencies (ranging from 4-40) which are one point data (No replicate ...
29 views

### Apply Fisher's exact test on multiple class

I am testing the presence of viruses within samples, which are matched 'normal', 'cancer' and 'metastasis'. I am testing the presence of viruses at species, family and order level. For instance, I ...
64 views

### Interpreting Fisher's test and power analysis in R

Currently I want to check whether there is a significant difference between the data from two clusters with n1 = n2 = 6. ...
30 views

### What statistical test could I use to compare categories of two data sets (for enrichment) with hugely different sample size?

I have some biological variant effect prediction data. This data can be split into categories based on the biological effect each variant has. I've turned this into two data sets: One is the "full" ...
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### Should a statistical test be performed if power is very low?

I performed some partitioning of data set (genes) into two lists, resulting in two enrichment lists. I wanted to compare them with Fisher's test, but from before I know that similarly looking results ...
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### GLM and fisher.test give different conclusion regarding factor significance

I would like to test the significance of a binary factor cropBin on a binary variables scaleBin. Here is the data : ...
144 views

### How do you check if expected cell counts are less than 5 when run Fisher's in R?

So I have gender (F,M) and blood pressure (Low, High) variables. I have 30, 100, 1, 5 in the observed cells. I understand that you use Fisher's exact test when one or more expected values are less ...
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### Fisher's Exact Test and bonferroni correction in r

I try to find out whether there are significant differences in Categories between several groups. My data looks like: ...
425 views

### Interpreting infinite odds ratio and confidence interval from Fisher's test

I've performed a two-sided Fisher's exact test on the following data, and the results include Infinity for the upper confidence interval and odds ratio. Are these results erroneous, and if not how do ...
19 views

### Interpretation of chisquare and odds ratio

I am studying te association between variables and used the chisquare test and the odds ratio of fisher exact test. I would like to know the exactly interpretation that i can do. The main variable is ...
247 views

### Differences in Fisher exact test statistic

I am trying to perform Fisher test on the following matrix: 269 118 55 48 Several free websites including R fisher.test() ...
41 views

### Statistical test for differences in proportions, over-dispersed count data

I have a nxm contingency table where I have counts of elements divided by type. For example: I would like to know if the proportions of any of the columns are different (i.e., is the G1/G2 proportion ...
41 views

### Fisher Exact / Chi Squared Type I/II for low expected counts

For a 2x2 contingency table, I understand when the expected frequency is less than 5 that using Fisher's exact test is preferred (I recall reading it is done so that a multinomial is approximately ...
48 views

### Which analysis should I use

I am comparing data from two cohorts of patients that underwent a surgical procedure: Group 1 (2013-2015, n=157) and Group 2 (2016-2018, n=146). In both cohorts, I have patients that had survived and ...
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### How does fisher.test calculate the confidence interval for the odds ratio in R?

The fisher.test function in base R by default returns a confidence interval for the odds ratio in a 2x2 contingency table. For example: ...
18 views

### Strange odds ratio (OR) derived from Fisher's test

I have frequency data for about 1000 genetic marker for two groups that I want to compare them between the two groups. I used Fisher’s test (in R) on the count data and got FDR and odds ratio (OR) for ...
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### Are the classic assumptions for Chi 2 test still valid?

For a 2*2 table, I want to use Chi 2 test Are the classic assumptions (1# more than 80% of the contingency cells having expected values ­> 5, 2# no zero in the cells ) are still valid? Is existence of ...
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### Is Fisher's exact test the most powerful test for 2x2 contingency table?

I don't find the powerfulness of Fisher's exact test on Wikipedia. Are there any results about the power of FET vs other methods on 2x2 contingency tables?
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### Analysing contingency table with small samples

My question is about how to analyse very small samples on contingency tables. I have a contingency table with observation for 2 groups (first variable) answering questions with multiple choices (...
57 views

### What test to use when a chi-squared assumption is violated but my contingency table only has one row?

I have some data of lizard counts near rock piles of different types that I'm trying to analyse. There are three different types of rocks (control, design 1, and design 2) and I have a lizard count ...
150 views

### Does multiple pairwise fisher exact test need multiple testing correction?

I am aware of that multiple testing correction is needed when multiple hypothesis tests are simultaneously performed. However, I am a little confused by the word "simultaneously". Say I have ...
31 views

### Fisher's Exact Output Interpretation - Genstat

I'm working with Fisher's Exact Test in Genstat with data classified into a $2\times 2$ contingency table. The output I have got from performing this test it below, but I am unsure which $p$-value is ...
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### Can I use a fisher's exact test for repeated measures?

I have a set of data working with embryos where I want to compare whether male carriers of a disease have a higher chance of outcome A than female carriers. My first thought was to do a fisher's ...
251 views

### Fisher's exact test: 95% CI or p-value

I have run proc freq to test association between two binary variables using the Fisher's exact test. However, the outputs seem contradict to each other as Two-sided Pr <= P 0.0355 whereas the OR ...
299 views

### Understanding “table margins”

I'm working on a statistics quiz and asked the following: What tables (with the same margins) would constitute stronger evidence of a gender bias effect in the calculation of the p-value using ...
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### Chi Square and Fisher’s exact test with Monte Carlo

SPSS can’t calculate Exact test for 4x7 table of my data so I did it with Monte Carlo. The output is given below. Considering the rules of Chi-square, I should use Fisher’s $p$-value for the result of ...
176 views

### How IBM SPSS calculates exact p value for Pearson Chi-Square statistic?

Usually, I use Fisher's exact test p value when the sample size is small for Pearson chi-square test. Then I realized that IBM SPSS reports exact p values for all the tests (i.e. Pearson Chi-Square, ...
66 views

### co-occurence and mutual exclusivity of two events

I would like to compute co-occurence and mutual exclusivity for a set of events divided in two groups (A and B). Each event E_{x,y} represents if a mutation occurs ...
31 views

### Test statistical significance with small number - Fisher's exact test

Before the part of the question related to the title, here is some background: I'm build a model that tries to predict a binary outcome ($Y$), given a set of features. Some of this features are ...
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### If I have less than 5 elements in a cell is there a way to use Chi Squared? [duplicate]

I have some data which has less than 5 elements in a cell, which would usually lead to fishers test being used instead. However, I'm unable to use fishers as there's not enough memory for it. chi ...