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Unformatted text preview: Engineering Statistics ENGRD270 Homework 2: Descriptive Statistics (contd) Spring 2007 Hand in by 1pm on Fri, Feb 9 in the ENGRD270 dropbox (2nd Floor Rhodes). Be sure to write your name and section number (16) or day&time on your homework. 1. The handy formula for the sample correlation coefficient. For a sample of pairs ( X 1 ,Y 1 ) ,..., ( X n ,Y n ), show the alternate formula r = [ X X i Y i- n X Y ] / [( n- 1) S X S Y ] . Here S 2 X = [ X 2 i- n X 2 ] / ( n- 1) and similarly S 2 Y . [ Hint: Study the computing formula for the sample variance in Devore 6e, page 39.] 2. Download the data file Marriage.mtw (MINITAB format) or Marriage.xls (ExCel format) from this website. These show the marriage and divorce rates per 1000 in the U.S. at 5 year intervals from 1920 to 1990. Construct a digidot plot for the marriage rates. Be careful about how you choose the stem increment. (MINITAB does not have a direct facility for producing digidot plots, so you need to do this by hand or use some cut-and-pasting.) 3. Download the data file Parkinsn.mtw (MINITAB format) or...
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- Spring '05