17.9 The chi-squared (X^2) test

• Epistasis arises when the allele of one gene affects or masks the expression of another in the phenotype.
• The chi-squared test is used to test the null hypothesis. The null hypothesis is based on the assumption that there will be no statistically significant difference between our observations.
• Degrees of freedom equals the number of categories minus 1.
• The chi-squared test can be used if the following conditions are met: the sample size is relatively large, the data falls into discrete categories and the data is expressed as raw results and not percentages.
• The chi-squared expression can be defined as follows: chi-squared = sum of (observed numbers - expected numbers)^2 / expected numbers.
• The critical value in the chi-squared test is p=0.05. If the probability found is equal to or greater than 0.05, the deviation is said to be not significant. Therefore, the null hypothesis is accepted.