F-distribution
In probability theory and statistics, the F-distribution or F-ratio, also known as Snedecor's F distribution or the Fisher–Snedecor distribution (after Ronald Fisher and George W. Snedecor), is a continuous probability distribution that arises frequently as the null distribution of a test statistic, most notably in the analysis of variance (ANOVA) and other F-tests. == Definitions == The F-distribution with d 1 {\displaystyle d_{1}} and d 2 {\displaystyle d_{2}} degrees of freedom is the distribution of X = U 1 / d 1 U 2 / d 2 {\displaystyle X={\frac {U_{1}/d_{1}}{U_{2}/d_{2}}}} where U 1 {\textstyle U_{1}} and U 2 {\textstyle U_{2}} are independent random variables with chi-square distributions with respective degrees of freedom d 1 {\displaystyle d_{1}} and d 2 {\displaystyle d_{2}} .