![]() ![]() Take a sample S1 comprising n1 observations, of mean µ1 and variance s1². Let D be the assumed difference between the means (D is 0 when equality is assumed).Īs for the z and t tests on a sample, we use: Take a second sample S2, independent of S1 comprising n2 observations, of mean µ2 and variance s2². Student's t test if the true variance of the populations from which the samples are extracted is unknown.The z test if the true variance s² of the population is known. ![]() The use of Student's t test requires a decision to be taken beforehand on whether variances of the samples are to be considered equal or not. If we consider that the two samples have the same variance, the common variance is estimated by: XLSTAT gives the option of using Fisher's F test to test the null hypothesis of equality of the variances of the groups (samples) and to use the result of the test in the subsequent calculations. ![]()
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