In Myers, Classical and Modern Regression with Applications (Duxbury Classic Series, 2nd edition, 1990), an experiment is described in which the Environmental Protection Agency seeks to determine the effect of two water treatment methods on magnesium uptake. Magnesium levels in grams per cubic centimeter (cc) are measured, and two different time levels are incorporated into the experiment. The data are as follows:
Â
Time (hr)
Treatment
1
2
2.19
2.15
2.16
2.03
2.01
2.04
1.88
1.86
1.91
(a) Do an interaction plot. What is your impression?
(b) Do an analysis of variance and show tests for the main effects and interaction.
(c) Give scientific findings regarding how time and treatment influence magnesium uptake.
(d) Fit the appropriate regression model with treatment as a categorical variable. Include interaction in the model.
(e) Is interaction significant in the regression model?
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