02-23-2011 2 Variance

02-23-2011 2 Variance - 2/23/2011 Lecture10:February23,2011...

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2/23/2011 1 Lecture 10: February 23, 2011 Today: Finish Comparing Two Variances (pp. 417 424) This is the first topic for Exam 2. Connect Homework 7: Problem 10.14, page 424: Topic–Paired differences Closes: Friday, February 25, 9:00 a.m. Connect Quiz No.1 Closes Thursday, February 24 at 6:00 p.m. Exam 1: Friday, February 25. It begins at 3:30 p.m. Seating: I’ll send an e mail announcement. Connect Homework 8: Topic: Comparing Two Variances Opens sometime Friday or Saturday Closes Tuesday, March 1. Return to the final slide from last class. The picture is very telling. Pay attention to: its shape its starting value on the horizontal axis units on the horizontal axis the approximate location of the number “1” on the horizontal axis. The picture is our template for an eventual hypothesis test. General Appearance of F It is skewed to the right. It cannot be negative: because it is the ratio of two variances and a variance cannot be negative a variance is in “squared” units It starts at zero. The picture above appears in the upper right hand corner of each table of critical values for F. (See, for example, page 419 or pages 768 775 of the text. Notice that the value F calc will eventually fall along the horizontal axis of the picture above.
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2/23/2011 2 How to find critical values using the F table For a left tailed test, you’ll need a critical value in the left tail. Call it F L . For a right tailed test, you’ll need a critical value in the right tail. Call it F R .
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02-23-2011 2 Variance - 2/23/2011 Lecture10:February23,2011...

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