Summary comprises of Textbook and Lecture Notes.
Undertstanding when to apply two sample hypothesis tests regarding the difference in means (one-sided/two-sided t tests and equal/unequal variances); The assumptions underlying the two sample hypothesis testing; How to construct confidence intervals;...
Paired sample t-test Do the two populations have
equal variances?
Yes No
Two-sample t-test for Two-sample t-test with
Homoscedastic equal variances unequal variances
Heteroscedastic (standard method) (Behrens-Fisher test)
, Homoscedastic – Two sample t-test for equal variances
Assumptions:
• The two samples (experimental units) were selected randomly
• The two sets of treatment levels are independent
• The population follows a normal distribution
• The two populations have equal variances
̅𝟏 − 𝑿
We are testing for difference between means 𝑿 ̅𝟐
(𝑋̅1 − 𝑋̅2 ) − 𝜇0
𝑡=
𝑠𝑋̅1 −𝑋̅2
…………………………………………………………………………………………….
Standard error of 𝑋̅1 − 𝑋̅2 :
Because we are assuming equal variances we get a more accurate estimate
by pooling the two groups into a common variance 𝑠𝑝2 :
If we have a balanced design:
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