P5510 Homework 3
1. (From Rosenberg, 1990). A study was done to compare the level of protection afforded by seat belts versus air
bags at two different impact speeds (30 mph and 45 mph). A fleet of 28 standard test vehicles was randomly
divided into two groups of 14 each. The 14 vehicles in one group were fitted with seat belts and the other 14 were
fitted with air bags. Special test mannequins were constructed from materials designed to simulate human skeletal
and tissue characteristics, and one mannequin was installed in each vehicle. Half of the vehicles equipped with seat
belts and half of the vehicles equipped with air bags were run into a solid wall at 30 miles per hour and the
remaining vehicles were run into the wall at 45 miles per hour.
Following each crash test, trauma points (fractures, lacerations, etc.) were identified and counted for each
mannequin. The data are summarized in the following table.
Impact Speed Condition
30 MPH
45 MPH
Seat Belts
Safety Condition
Air Bag
3
4
3
3
1 Mean = 3.0
3
4
3
0
1
1
4 Mean = 2.0
0
5
7
6
9
9
5 Mean = 7.0
8
5
4
7
4
3
Mean = 4.0
3
5
2
Mean = 5.0
Mean = 2.5
Mean = 5.5
Mean = 3.0
Perform an analysis of these data using REGRESSION and contrast coding schemes for factorial designs as outlined
in lecture..
Perform the same analysis using GLM and show that you get the same p-values for both main effects and for the
interaction.
Describe the result of each test appropriate for such data.
In addition to the above description, submit a screen shot of printout of the data editor so I can make sure you did
the contrast codes correctly.