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Chi-squared distribution, showing χ2 on the x -axis and p -value (right tail probability) on the y -axis. A chi-squared test (also chi-square or χ2 test) is a statistical hypothesis test used in the analysis of contingency tables when the sample sizes are large. In simpler terms, this test is primarily used to examine whether two categorical ...
The chi-squared distribution is obtained as the sum of the squares of k independent, zero-mean, unit-variance Gaussian random variables. Generalizations of this distribution can be obtained by summing the squares of other types of Gaussian random variables. Several such distributions are described below.
Each line shows one of the three possible genotypes. In population genetics, the Hardy–Weinberg principle, also known as the Hardy–Weinberg equilibrium, model, theorem, or law, states that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences.
Fisher's exact test is a statistical significance test used in the analysis of contingency tables. [1] [2] [3] Although in practice it is employed when sample sizes are small, it is valid for all sample sizes. It is named after its inventor, Ronald Fisher, and is one of a class of exact tests, so called because the significance of the deviation ...
Genome-wide association study. In genomics, a genome-wide association study ( GWA study, or GWAS ), is an observational study of a genome-wide set of genetic variants in different individuals to see if any variant is associated with a trait. GWA studies typically focus on associations between single-nucleotide polymorphisms (SNPs) and traits ...
Relation to the chi-squared test. The commonly used chi-squared tests for goodness of fit to a distribution and for independence in contingency tables are in fact approximations of the log-likelihood ratio on which the G-tests are based. The general formula for Pearson's chi-squared test statistic is
The transmission disequilibrium test ( TDT) was proposed by Spielman, McGinnis and Ewens (1993) [1] as a family-based association test for the presence of genetic linkage between a genetic marker and a trait. It is an application of McNemar's test . A specificity of the TDT is that it will detect genetic linkage only in the presence of genetic ...
Linkage disequilibrium. In population genetics, linkage disequilibrium ( LD) is a measure of non-random association between segments of DNA ( alleles) at different positions on the chromosome ( loci) in a given population based on a comparison between the frequency at which two alleles are detected together at the same loci and the frequencies ...