STAT10x10.11.05TwoSampleTests

STAT10x10.11.05TwoSampleTests - Two-sample tests of means...

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Unformatted text preview: Two-sample tests of means in MINITAB : use Stat Basic Statistics Two-sample-t. Data can be entered in separate columns, or in a single column with a variable indicating treatment group (the subscript column). Click options to set confidence/alpha level and to specify one or two-sided test. Two-Sample T-Test and CI: Dry Weight, Group Two-sample T for Dry Weight Group N Mean StDev SE Mean 0% 3 1.513 0.496 0.29 100% 3 0.00833 0.00945 0.0055 Difference = mu (0%) - mu (100%) Estimate for difference: 1.50500 95% lower bound for difference: 0.66914 T-Test of difference = 0 (vs >): T-Value = 5.26 P-Value = 0.017 DF = 2 Note : in MINITAB, there is no need to specify - compare your threshold for rejection to the p-value. Now : whats up with this? Where is the other side of the confidence interval??? This is called a non-central confidence interval. STAT 101a-105a Introduction to Statistics 215 So far, we have made central confidence intervals which are symmetric around the sample mean : 2 2 2 1 2 1 2 2 1 ) ( n s n s t x x + - This is equivalent to a two-sided hypothesis test. NOW : if we are certain that, for example, RoundUp will not make plants grow, we use a one-sided hypothesis test. In this case, we can make a one-sided, or non- central confidence interval : +-- , ) ( 2 2 2 1 2 1 2 1 n s n s t x x In this case, MINITAB only reports the lower bound STAT 101a-105a Introduction to Statistics 216 95% 2.5% 2.5% Central Confidence I nterval 95% 5% Non-Central Confidence I nterval Upper bound is positive infinity. t is critical value that makes area to the left = Central Confidence Intervals are BY FAR the most common type of confidence interval. Non-central confidence intervals do get used on occasion in applications such as engineering, biology, medicine. Central vs. Non-Central Confidence Intervals in MINITAB : use Stat Basic Statistics Two-sample-t. Click options - choose Not Equal for a central confidence interval and a two- sided test. Choose Greater than or Less Than for a non- central confidence interval and a one-sided test....
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STAT10x10.11.05TwoSampleTests - Two-sample tests of means...

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