# 420Hw12 - STAT 420(10 points(due Friday November 21 by 3:00...

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STAT 420 Fall 2008 Homework #12 (10 points) (due Friday, November 21, by 3:00 p.m.) ppm mV 0 1.72 0 1.68 0 1.74 50 2.04 50 2.11 50 2.17 75 2.40 75 2.32 75 2.33 100 2.91 100 3.00 100 2.89 150 4.47 150 4.51 150 4.43 200 6.67 200 6.66 1. Chemists often use ion-sensitive electrodes (ISEs)to measure the ion concentration of aqueous solutions. These devices measure the migration of the charge of these ions and give a reading in millivolts ( mV ). A standard curve is produced by measuring known concentrations ( in ppm ) and fitting a line to the millivolt data. The table on the right gives the concentrations in ppm and the voltage in mV for calcium ISE. a) Plot the points mV ( y ) versus ppm ( x ). Does linear model seem to be appropriate here? b) Use the Box-Cox method to determine the best transformation on the response variable mV. c) In part (a), a linear model does not seem appropriate. Fit a quadratic model. Does it seem to provide a better fit? 200

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## This note was uploaded on 05/09/2010 for the course MATH 420 taught by Professor Stepanov during the Spring '10 term at University of Illinois, Urbana Champaign.

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420Hw12 - STAT 420(10 points(due Friday November 21 by 3:00...

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