![\"f1\"](\"http:\/\/sites.ulethbridge.ca\/science-toolkit\/files\/2016\/07\/f1.gif\")
<\/p>\nWhat it’s for:<\/p>\n
The F test compares two samples to test the null hypothesis that they have equal variance. This may be of direct interest, but the F test is also often used in conjunction with a t-test. We use a different formula to calculate t if variances are unequal, so before running a t-test we often run an F test. If the null hypothesis is not rejected in the F test, we have no reason to believe the variances of our two populations are different, so we would use the t-test formula assuming equal variance. If the null hypothesis is rejected in the F test, we would use the t-test formula assuming unequal variances.<\/p>\n
Assumptions\/Cautions:<\/p>\n
Test is parametric — data must be normally distributed (Zar 1996).
\nHow to use it:<\/p>\n
1) Calculate the variance for each of your samples.<\/p>\n
2) Calculate F by dividing the larger variance by the smaller variance, as shown in the box to the right (Zar 1996).<\/p>\n
3) Calculate the numerator degrees of freedom as n1-1, where n1 is size of the sample with the larger variance.<\/p>\n
4) Calculate the denominator degrees of freedom as n2-1, where n2 is the size of the sample with the smaller variance.<\/p>\n
5) Estimate the p-value associated with your F statistic, using a computer program or table.<\/p>\n
6) Draw a conclusion, based on the p-value from 5). See also Types of Error.<\/p>\n
MS Excel Tips:<\/p>\n
MS Excel can calculate the probability associated with your calculated F statistic, using the FDIST function. However, Excel calculates a one-tailed probability. For most uses of the F test, a two-tailed probability is more appropriate (Zar 1996), so you must multiply Excel’s p-value by 2. Excel also has a built-in FTEST function which directly calculates F and the associated probability value from raw data, but this function may misreport F, and is not recommended.<\/p>\n
RETURN<\/p>\n","protected":false},"excerpt":{"rendered":"
What it’s for: The F test compares two samples to test the null hypothesis that they have equal variance. This may be of direct interest, but the F test is also often used in conjunction with a t-test. We use a different formula to calculate t if variances are unequal, so before running a t-test … Continue reading The F Test<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":65,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":"","_links_to":"","_links_to_target":""},"class_list":["post-69","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/sites.ulethbridge.ca\/science-toolkit\/wp-json\/wp\/v2\/pages\/69","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/sites.ulethbridge.ca\/science-toolkit\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/sites.ulethbridge.ca\/science-toolkit\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/sites.ulethbridge.ca\/science-toolkit\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/sites.ulethbridge.ca\/science-toolkit\/wp-json\/wp\/v2\/comments?post=69"}],"version-history":[{"count":3,"href":"https:\/\/sites.ulethbridge.ca\/science-toolkit\/wp-json\/wp\/v2\/pages\/69\/revisions"}],"predecessor-version":[{"id":258,"href":"https:\/\/sites.ulethbridge.ca\/science-toolkit\/wp-json\/wp\/v2\/pages\/69\/revisions\/258"}],"up":[{"embeddable":true,"href":"https:\/\/sites.ulethbridge.ca\/science-toolkit\/wp-json\/wp\/v2\/pages\/65"}],"wp:attachment":[{"href":"https:\/\/sites.ulethbridge.ca\/science-toolkit\/wp-json\/wp\/v2\/media?parent=69"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}