Questions tagged [fishers-exact]

A hypothesis test for contingency tables.

Filter by
Sorted by
Tagged with
1
vote
1answer
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). ...
1
vote
1answer
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 ...
1
vote
0answers
22 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 ...
2
votes
0answers
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....
0
votes
1answer
46 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 ...
2
votes
1answer
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. ...
12
votes
1answer
627 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 ...
0
votes
0answers
7 views

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 ...
1
vote
1answer
59 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. ...
1
vote
1answer
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 ...
2
votes
0answers
30 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 ...
0
votes
1answer
16 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 ...
0
votes
0answers
7 views

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 (...
0
votes
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 ...
1
vote
0answers
10 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 ...
0
votes
0answers
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 ...
1
vote
0answers
78 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. ...
0
votes
1answer
33 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. ...
0
votes
0answers
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 ...
0
votes
0answers
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 ...
2
votes
1answer
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. ...
1
vote
0answers
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" ...
1
vote
0answers
36 views

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 ...
1
vote
1answer
29 views

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 : ...
2
votes
4answers
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 ...
0
votes
0answers
92 views

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: ...
0
votes
2answers
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 ...
0
votes
0answers
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 ...
2
votes
3answers
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() ...
0
votes
0answers
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 ...
2
votes
1answer
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 ...
2
votes
2answers
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 ...
2
votes
1answer
482 views

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: ...
0
votes
1answer
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 ...
0
votes
0answers
21 views

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 ...
1
vote
1answer
58 views

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?
0
votes
0answers
39 views

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 (...
0
votes
1answer
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 ...
2
votes
1answer
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 ...
0
votes
0answers
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 ...
0
votes
0answers
86 views

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 ...
1
vote
1answer
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 ...
2
votes
1answer
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 ...
0
votes
1answer
256 views

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 ...
0
votes
1answer
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, ...
0
votes
1answer
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 ...
0
votes
2answers
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 ...
0
votes
0answers
39 views

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 ...
1
vote
1answer
166 views

Fisher exact test for mutation co-occurence

I've a dataset of 492 samples, for each sample I've information regarding if gene X has a germline mutation and a somatic mutation. I would like to test co-occurence of germline and somatic mutation ...
4
votes
2answers
2k views

Fisher exact test on 4 x 3 table, with low count?

I'm thinking about applying Fisher Exact Test for the following contingency table: ...