You'll need to define five Excel names, which can be either defined constants or (preferably) references to worksheet cells, as follows: Here is how you can go about calculating it in Excel. The general formula for the F distribution's cumulative density function is lengthy and intimidating, but it can be found in a variety of online sources. =1-FDIST(2.4,5,50) Calculating the Cumulative Density Function Which returns the value 0.95, or FDIST() prior to Excel 2010: You can verify this using Excel's F.DIST() function: In other words, 95% of the observations from a central F distribution with 5 and 50 degrees of freedom have F-ratios of 2.4 and less. For example, the cumulative density function for the central F-ratio with 5 and 50 degrees of freedom, at a value of 2.4, is 95%. The cumulative density function is the probability that a variable such as the F-ratio will have a value equal to or smaller than the one specified. The third article discusses the effect of the noncentrality parameter on the F distribution's probability density function.Īs you might expect, the noncentrality parameter is used in the formulas for both the F distribution's cumulative density function and its probability density function. The concept of statistical power is discussed in the first article in this series, and the statistical power of the t-test is discussed in the second article. This article, the fourth in a four-part series, discusses the relationship of the noncentrality parameter to the F distribution's cumulative density function-and therefore the power of the F test.
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