# 9.2. One Tail Hypotheses Testing.pptx - One tail vs Two...

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One tail vs Two tail tests Recall in the assembly time example (video 9.1) H0: μ = 130 H A : μ Rejection region at 5% level of significance: Reject H0 If or ? > 1.96 means that mean of the selected sample is very much larger than 130 (i.e. it falls in the rejection region on the right) ? < 1.96 means that mean of the selected sample is very much smaller than 130 (i.e. it falls in the rejection region on the left) Two-tail test: We look at both tails of the distribution 1
One vs two tail tests We may have claims or beliefs that require only one tail in the rejection region 1. μ is at least 130 (or less than 130)? 2. μ is no less than 125 (or greater than 125 Left Tail Hypothesis , Assembly line example: Claims that say that Right Tail Hypothesis , 2
Two-tail test The rejection area of each tail will be equal to /2 . Hypotheses: H0: μ=μ0 HA: μ μ0 Reject H0 if calculated z > z α/2 or calculated z < - z α/2 Rejection Region: 3
One-tail tests The area of the whole left tail will be equal to .
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