Homework 11
MATH 4830, Spring 2006
due Thurs. April 27

1. p. 197, Problem 14: Planet Distance from Order of Sun

   Recall, you can read the data into R with

   > planets <- read.table(``http://www-math.cudenver.edu/~bbailey/4830/planets.dat'', header=T)
   

   For part (d) Compute the estimate of sigma in R!

2. Yearly Mean Ozone Concentration:

   Is there evidence that the ozone layer is changing over time?

   The data we will analyize is the yearly mean concentration (in Dobson units) of the ozone layer
   at Arosa, Switzerland, from 1926 to 1971 (from Andrews and Herzberg, 1985, p. 75-76).

   • Use the read.table command to make a dataframe from the file oz.dat
     The column headings are ymozone (yearly mean ozone) and year.
   • Plot the data over time.
   • Fit a a linear model to the data. Superimpose the fitted straight line over the plot of the data.
   • What is the 95% CI for you estimate of the slope of the line? What is your conclusiion about a trend over time?

3. Multiple Regression: p. 260, Problem 13

4. Mutiple Regression and Model Selection: p. 260-261, Problem 14.

   You can read the data into R with

   > pace <- read.table(``http://www-math.cudenver.edu/~bbailey/4830/pace.dat'', header=T)
   

   Part 2: Use the R function step and perform model selection. What is the best model based on AIC?