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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.
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 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.
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 textbook method is to compare the observed value of F with the critical value of F determined from tables. The critical value of F is a function of the degrees of freedom of the numerator and the denominator and the significance level (α). If F ≥ F Critical, the null hypothesis is rejected.
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.
While the Kolmogorov–Smirnov test is usually used to test whether a given F(x) is the underlying probability distribution of F n (x), the procedure may be inverted to give confidence limits on F(x) itself. If one chooses a critical value of the test statistic D α such that P(D n > D α) = α, then a band of width ±D α around F n (x) will ...
Most uses of the Fisher test involve, like this example, a 2 × 2 contingency table (discussed below). The p-value from the test is computed as if the margins of the table are fixed, i.e. as if, in the tea-tasting example, Bristol knows the number of cups with each treatment (milk or tea first) and will therefore provide guesses with the ...