Exercise 4:    one-way ANOVA*

 

In a study one measured the sorption rate of three different types of organic chemical solvents. These solvents are used to in the industy to clean metal parts and are potential hazardous waste. Independent samples from each type of solvent were tested and their sorption rates were recorded (as mole percentages).  The results are given in the table below:

 

1) Aromatics	1.06, 0.79, 0.82, 0.89, 1.05, 0.95, 0.65, 1.15, 1.12
2) Chloroalkanes	1.58, 1.45, 0.57, 1.16, 1.12, 0.91, 0.83, 0.43
3) Esters	0.29, 0.06, 0.44, 0.55, 0.61, 0.43, 0.51,0.10, 0.53, 0.34, 0.06, 0.09, 0.17, 0.17, 0.60

 

a) Read the data into R by the command:

solvents=read.table("http://www.uio.no/studier/emner/matnat/math/STK4900/data/solvents.txt",header=T)

Inspect the data and make sure that you understand how the data are recorded.

 

b) Make a boxplot of the data:

boxplot(rate~type,data=solvents)

What does the boxplot tell you about the sorption rates of the different types of chemicals?

 

c) Perform a one-way ANOVA. (See slide 11 from the lectures for R-help.)

Make sure you understand the ANOVA table. Is there a significant difference in the sorption rates?

 

*) From: Walpole, Myers & Myers: Probability and Statistics for engineers and scientists, Prentice-Hall