STA 242/ENV 255

LAB1: Introduction to UNIX workstations, SAS, and OLS

Lab Goals:

1. Create a SAS Data set
2. Carry out a simple linear regression and interpret results and residual plots

ASSIGNMENT: Problems 1-6 in Chapter 2, Regression with Graphics (RWG)

References

1. Chapter 1: Starting SAS INSIGHT
2. Chapter 2: Entering Data
3. Chapter 4: Exploring Data in One Dimension
4. Chapter 12: Examining Distributions
5. Chapter 13: Fitting Curves

Topics

1. Starting SAS from UNIX
2. Reading in a SAS data set
3. Starting SAS/INSIGHT
4. Fitting Regression Models
5. Confidence Intervals
6. Hints for problem 3
7. Hints for problem 4
8. Hints for problem 5
9. Hints for problem 6: Excluding Points
10. Printing your results

Starting SAS

To start up SAS enter

	sas &

Creating a SAS Data Set via the Program Editor

To enter a data set using the Program editor, follow the steps in the following sample (don't forget the semi-colon!!!).You should type these statements in the PROGRAM EDITOR window. Italics indicate names specific to this data set that you can change as you like.

data sasuser.rwg59;
input stream $ 1-13 summerph fish ;
datalines;
Moss                6.3            6
Orcutt              6.3            9
Ellinwood           6.3            6
Jacks               6.2            3
Riceville           6.2            5
Lyons               6.1            3
Osgood              5.8            5
Whetstone           5.7            4
Upper Keyup         5.7            1
West                5.7            7
Boyce               5.6            4
Mormon Hollow       5.5            4
Lawrence            5.4            5
Wilder              4.7            0
Templeton           4.5            0
; {NOTE: this semicolon tells SAS that this is the end of the data}
run;

Note all data sets from RWG are available from the course web page Data Sets. You can download these to your home directory. File names are of the form "rwg.##" where ## is the page number in the text. If you have saved the data as an ordinary text file, say "rwg.59", then the commands to create the SAS data set for the assignment are:

data sasuser.rwg59;
infile 'rwg.59';
input stream $ 1-13 summerph fish;
run;

To get SAS to process these commands, go to the Locals pull-down menu and choose Submit. You should see "NOTE: 16 Lines submitted." You now have a SAS data set to use. If you don't see this, then there may be some typo or error in the commands. If you were successful, you created a SAS data set called rwg59, that is stored in your SAS library called SASUSER. The data set contains three variables called stream,summerph and fish that correspond to the 3 columns of numbers.

Starting SAS/INSIGHT

Now, to start up INSIGHT, follow these menus from the PROGRAM EDITOR: Use the mouse to select the Globals menu, and then select

1. Globals
2. Analyze ->
3. Interactive data analysis

Fitting Regression Models (Ch 13 INSIGHT)

Select the variable FISH, then press the Y button to specify that FISH is the dependent or response variable. Now put SUMMERPH in the X area. Click on STREAM, then press the Label button. This will be used to label points in graphs, etc.

A new window will appear with a scatterplot of the data and regression line, summary statistics of the regression, and residual plots. Refer to this output to answer Problems 1 and 2.

You can add the CI curves shown in fig 2.7 of RWG to the regression line by:

• Select Curves->Confidence Curves->Mean:95% for the 95% confidence interval
• Select CurvesConfidence Curves->Prediction: 95% for the prediction interval

Hints for Problem 3

TSSx

This is calculated by multiplying the variance of X by (n-1) which is CSS. (Corrected Sum of Squares)

X bar

This is the mean, found in the distribution window

Xi

This is the value of X you are predicting things about: 6

se

This is the Root MSE, found in the FIT window

t

This value comes from the chart on 350 in the back of RWG It is NOT the t-statistic from the output! The degrees of freedom are from the ANOVA table in the ERROR line.

Y hat

This is the predicted value of Y when X=6. Use your regression equation to calculate the value.

Hints for Problem 4

Find the points with the largest absolute residuals is to

• Create a variable for abs(e): select R_FISH, go to the menu Edit:Variables:Other and select the transformation abs(), select o.k.
• Plot A_R_Fish versus SUMMERPH: Go to Analyze:ScatterPlot (Y,X); select A_R_Fish as Y and SUMMERPH as X
• Use the arrow to click on a point, and the stream name is displayed
• To choose more than one point to highlight, hold down the Ctrl key as you are pressing the mouse button
• In the data window there is a little arrow in the upper left hand corner. Click it, and then select Sort... in the pop-up menu. Select the variable A_R_FISH and click on Y to sort the data by the absolute values of the residuals. In this problem, this may seem like a lot of work to find the largest absolute residuals, but it is useful for large data sets.

Hints for Problem 5

• Create a normal Quantile plot, by going to the Graph menu and selecting QQ plot. In the pop-up menu, select Normal, and then click on OK.
• Add a Normal density to the histogram of the residuals, by selecting the menus Curves:Parametric Density, and then Normal.

• In the DATA window, select the two points by highlighting the observation number.
• Choose these menus:
  • Edit
  • Observations ->
  • Exclude in calculations
• The graphics window is redrawn, and all the values in the tables are recalculated.

Printing and Saving a Graph

1. In the PROGRAM EDITOR WINDOW, go to the Menu VIEW and select Preferences... then Display Manager and finally click on "Use Host Printing". Click on OK.
2. Next go to the PROGRAM EDITOR window and select the FILE menu and click on" Print Setup...". Click on "Properties..." in the popup menu and then OK. You should see that the printer icon is cyan and blue now. Click on OK. Once you have done these two steps at the beginning of the session, your output will be saved to a file called "prn.ps" by default.

b) Now choose File:Print. Click on the box "Print File to Disk", and then PRINT. A window will pop up; in the box under "Enter directory name, filename or filter, specify a filename for the output, such as HW1reg.ps click on "OK", and select "Fill Page" on the next window that appears". Note, if you don not change the filenames, you will write over the old file. c) Go over to the UNIX window and type

ls

        print HW1reg.ps

        ghostview HW1reg.ps