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Unformatted text preview: Twosample tests of means in MINITAB : use Stat Basic Statistics Twosamplet. 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 twosided test. TwoSample TTest and CI: Dry Weight, Group Twosample 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 TTest of difference = 0 (vs >): TValue = 5.26 PValue = 0.017 DF = 2 Note : in MINITAB, there is no need to specify α compare your threshold for rejection to the pvalue. Now : what’s up with this? Where is the other side of the confidence interval??? This is called a noncentral confidence interval. STAT 101a105a 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 + ± α This is equivalent to a twosided hypothesis test. NOW : if we are certain that, for example, RoundUp will not make plants grow, we use a onesided hypothesis test. In this case, we can make a onesided, or non central confidence interval : ∞ + , ) ( 2 2 2 1 2 1 2 1 n s n s t x x α In this case, MINITAB only reports the lower bound STAT 101a105a Introduction to Statistics 216 95% 2.5% 2.5% Central Confidence I nterval 95% 5% NonCentral Confidence I nterval Upper bound is positive infinity. α t is critical value that makes area to the left = α Central Confidence Intervals are BY FAR the most common type of confidence interval. Noncentral confidence intervals do get used on occasion in applications such as engineering, biology, medicine. Central vs. NonCentral Confidence Intervals in MINITAB : use Stat Basic Statistics Twosamplet. 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 onesided test....
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This note was uploaded on 04/07/2008 for the course STAT 102 taught by Professor Jonathanreuningschererdonaldgreen during the Fall '05 term at Yale.
 Fall '05
 JonathanReuningSchererDonaldGreen
 Statistics

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