One tail vs Two tail testsRecall in the assembly time example (video 9.1)H0: μ= 130 HA: 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 distribution1
One vs two tail tests•We may have claims or beliefs that require only one tail in the rejection region1. μis at least 130 (or less than 130)?2. μis no less than 125 (or greater than 125 Left Tail Hypothesis•, Assembly line example: Claims that say thatRight Tail Hypothesis•, 2
Two-tail testThe rejection area of each tail will be equal to /2.Hypotheses:H0: μ=μ0HA: μμ0•Reject H0 if •calculated z > zα/2•or calculated z < - zα/2Rejection Region: 3
One-tail testsThe area of the whole left tail will be equal to .