STAT 420
Spring 2014
Homework 7:
Due April 4 by 7:00pm
Exercise 1 (revisited)
Chemists often use ionsensitive electrodes (ISEs) to measure the ion concentration of aque
ous 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 Ftting a line to the millivolt data. The below table gives the concentrations
in ppm and the voltage in mV for calcium ISE.
i
ppm
mV
i
ppm
i
ppm
1
0
1.72
7
75
2.40
13
150
4.47
2
0
1.68
8
75
2.32
14
150
4.51
3
0
1.74
9
75
2.33
15
150
4.43
4
50
2.04
10
100
2.91
16
200
6.67
5
50
2.11
11
100
3.00
17
200
6.66
6
50
2.17
12
100
2.89
18
200
6.57
(a) Plot the points mV (
y
) versus ppm (
x
). Overlay the leastsquares (linear) regression
line, and comment on whether the line seems to Ft the data.
(b) ±it a quadratic model. Overlay the leastsquares (quadratic) regression line; does it
seem to provide a better Ft?
(c) ±it a cubic model. Overlay the leastsquares (cubic) regression line; which model
(linear, quadratic, or cubic) do you choose and why?
Exercise 2
A survey was conducted to study teenage gambling in Britain. (IdeSmith & Lea, 1988,
Journal of Gambling Behavior, 4, 110–118) The data is stored in the data frame
teengamb
(library
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview.
Sign up
to
access the rest of the document.
 Spring '08
 Stepanov
 Statistics, Least Squares, Regression Analysis, Quadratic equation, Trigraph, Cubic function

Click to edit the document details