Statistics > Test for a Difference Between Two Means
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QuickNotes™  

Test for a Difference Between Two Means

  • If both independent sample are large or both populations from which the sample is selected are drawn from a normal distributions with known standard deviations, use the normal distribution to test μ1μ2.

  • If both independent sample are large or both populations from which the sample is selected are drawn from a normal distributions with unknown standard deviations, use the t-distribution with ν = n1 + n2 − 2 degrees of freedom to test μ1μ2 .

  • If the sample size is large or the population of paired differences is normally distributed with unknown standard deviations, then use the t-distribution with ν = n − 1 degrees of freedom to test μd .