S-PLUS INSTRUCTIONS FOR CASE STUDIES IN THE STATISTICAL SLEUTH

Transcription

1 S-PLUS INSTRUCTIONS FOR CASE STUDIES IN THE STATISTICAL SLEUTH Dan Schafer January, 2002 This guide contains brief instructions for accomplishing the graphical and numerical analyses of the case studies in The Statistical Sleuth, A Course in Methods of Data Analysis, 2 nd Edition by Ramsey and Schafer, using S-PLUS (S-PLUS 2000 Professionals Release 3). The data sets are available at Case Study 1.1. Motivation and Creativity 1. Importing the data from a file. a. From the main menu, left click Data. From the pop-up menu, click Select Data. b. Left click on Import File.

2 c. Fill in the resulting Import Data dialog box. Find the directory that contains the data Choose Click on the the correct desired file type data file name Click on Open 4 d. The data window should appear: Additional reading: S-PLUS User s Guide, Chapter 2: p (The User s Guide is available by left clicking on Help, the Online Manuals, then User s Guide. 2

3 2. Draw side-by-side box plots. Left click the 2D graph toolbar button to open the 2D graph palette 1 Left click on gray part of TREAT- MENT 2 column, then, while pressing CTRL, click on gray part of SCORE column Click the boxplot button 3 2D graph palette Result: 3

4 3. Two-sample t-test a. From the main menu, left click on Statistics. From the pop-up menu, click on Compare Samples, then Two Samples, then t Test. b. Fill in the Two-sample t test window as follows. Make sure the data set of interest is displayed here 1 Click on this box 3 Choose SCORE for Variable 1 and TREAT- MENT for Variable 2: 2 Click on OK or Apply 4 4

5 a. Result: 4. Further Notes: a. The instructions above depend on the grouping variable TREATMENT in this case being of the data type called factor. If the variable values are words, such as EXTRINSIC and INTRINSIC, then the variable will automatically be treated as a factor. If, instead, it is a numerical code, like 1 and 2, then the variable type must be changed to factor. To do this, right click on the column (in the gray area) so that the column is highlighted in black and a pop-up menu appears. Choose Change Data Type and follow the directions. b. You may click on the blue part of a graph page so that it is highlighted, type the letter c while holding down CTRL, and then paste the graph into a word processor, like WORD. With the cursor positioned at the desired location in the document, type CTRL v. Case Study 1.2. Sex Discrimination in Employment 1. Preliminaries. Importing the data file, drawing side-by-side box plots, and conducting the t-test are carried out with the same procedures as described above. 5

6 2. Editing a graph. a. To change a label, left click on it so that green boxes appear around it. Then right click so a pop-up menu appears. Edit as desired. 6

7 b. Changing box plot specifications. Place the cursor arrow inside one of the boxes, left click once, and then double click with the left mouse button, to get the following window: c. Click on the Box Specs tab. I prefer to change the top and bottom color of the boxplot to white and the Median color to black. 7

8 d. Add text. While the graph sheet is active (click on the top blue border to make it active), left click on Insert from the main menu, select Add text and fill in the dialog box. 8

9 Notes About Chapter 1 Computational Problems. 1. For problem 1.16: a. To enter data manually: Select Data from the main menu, click on New Data, supply a name (like ex0116), and then enter the data on the resulting spreadsheet. To supply column names, double click on the existing name (like V1) then type a new one. b. To draw the scatterplot in part b, highlight the ORDER column (by clicking on the gray part of the column), highlight the DISTANCE column (by clicking on the gray part) whiling pressing CTRL, then click on the scatterplot button in the 2D plot palette. c. To draw the plot on the log-log scale, scroll the plot type on standard tool bar so that Log Log shows. d. To get the average and standard deviation, click on Statistics from the main menu, then on Data Summaries and Summary Statistics. Fill in the dialog box then click on the Statistics tab and make sure checks are next to the desired summary statistics. Then click on OK. 9

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