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Test for the mean. Independent samples (Part1)

Test for the mean. Independent samples (Part1)

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In the exercise for this lesson I calculated everything correctly, however, I have chosen hypothesizes vice versa. For H0 = mean of ajaxplus – mean of ajax >0 and for H1 = mean of ajaxplus – mean of ajax < or equal to 0. So I rejected hypothesis which was actually true. How I could avoid this mistake. Does correctness of our result totally depend on chosen hypothesis?

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I think I figured it out. If we are dealing with one tailed test, we have to figure out is it left-tailed (rejection area on the left) or right-tailed (rejection area on the right). To reject null in left-tailed test we should have negative Z with p-value<alpha, if it is right-tailed then we should have positive Z with p-value<alpha. I don’t know why it is not included in the lesson. Please, correct me if I am wrong.

But now I am having problem determining between left and right tailed tests.

4 months