Minitab 16 version de prueba
^ The Satterthwaite Formula for Degrees of Freedom in the Two-Sample t-Test (page 7).Do two processes have the same mean?, Engineering Statistics Handbook, NIST. "Why Welchs test is Type I error robust" (PDF). ^ a b Derrick, B Toher, D White, P (2016)."The unequal variance t-test is an underused alternative to Student's t-test and the Mann–Whitney U test". "The generalization of "Student's" problem when several different population variances are involved". Oneway( Y( YColumn), X( XColumn), Unequal Variances( 1 ) ) T.test(data1, data2, alternative="two.sided", var.equal=FALSE) Microsoft Excel 2010 and later (Student's T Test)ĭefault output from proc ttest (labeled "Satterthwaite") Microsoft Excel pre 2010 (Student's T Test) Ttest2(data1, data2, 'Vartype', 'unequal')
#MINITAB 16 VERSION DE PRUEBA SOFTWARE#
Software implementations Language/Program For unequal variances, Welch's t-test gave p-values close to simulated p-values. So with actual data, the two tests will almost always give somewhat different results.įor unequal variances, Student's t-test gave a low p-value when the smaller sample had a larger variance (Example 2) and a high p-value when the larger sample had a larger variance (Example 3). But note that if you sample data from populations with identical variances, the sample variances will differ, as will the results of the two t-tests. Welch's t-test and Student's t-test gave identical results when the two samples have identical variances and sample sizes (Example 1). Welch's t-test defines the statistic t by the following formula:
Welch's t-test is an approximate solution to the Behrens–Fisher problem. Welch's t-test is designed for unequal population variances, but the assumption of normality is maintained. Student's t-test assumes that the two populations being compared are normally distributed with equal variances.