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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.
The F table serves as a reference guide containing critical F values for the distribution of the F-statistic under the assumption of a true null hypothesis. It is designed to help determine the threshold beyond which the F statistic is expected to exceed a controlled percentage of the time (e.g., 5%) when the null hypothesis is accurate.
Example: To find 0.69, one would look down the rows to find 0.6 and then across the columns to 0.09 which would yield a probability of 0.25490 for a cumulative from mean table or 0.75490 from a cumulative table. To find a negative value such as –0.83, one could use a cumulative table for negative z-values [3] which yield a probability of 0.20327.
The Pareto distribution, or "power law" distribution, used in the analysis of financial data and critical behavior. The Pearson Type III distribution; The phase-type distribution, used in queueing theory; The phased bi-exponential distribution is commonly used in pharmacokinetics; The phased bi-Weibull distribution
The resulting ratio, F max, is then compared to a critical value from a table of the sampling distribution of F max. [ 2 ] [ 3 ] If the computed ratio is less than the critical value, the groups are assumed to have similar or equal variances.
The critical value is the number that the test statistic must exceed to reject the test. In this case, F crit (2,15) = 3.68 at α = 0.05. Since F=9.3 > 3.68, the results are significant at the 5% significance level. One would not accept the null hypothesis, concluding that there is strong evidence that the expected values in the three groups ...
The α-level upper critical value of a probability distribution is the value exceeded with probability , that is, the value such that () =, where is the cumulative distribution function. There are standard notations for the upper critical values of some commonly used distributions in statistics:
C UL = upper limit critical value for one-sided test on a balanced design α = significance level, e.g., 0.05 n = number of data points per data series F c = critical value of Fisher's F ratio; F c can be obtained from tables of the F distribution [10] or using computer software for this function.