Statistics for psychology

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CHAPTER 15  PROBLEM 1

Use SPSS to analyze the data of Chapter 15, Problem 20, part b, p. 392 of the textbook.  For convenience, the problem is repeated here.

A sleep researcher conducts an experiment to determine whether sleep loss affects the ability to maintain sustained attention.  Fifteen individuals are randomly divided into the following three groups of five subjects each: group 1, which gets the normal amount of sleep (7-8 hours); group 2, which is sleep-deprived for 24 hours; and group 3, which is sleep-deprived for 48 hours.  All three groups are tested on the same auditory vigilance task.  Subjects are presented with half-second tones spaced at irregular intervals over a 1-hour duration.  Occasionally, one of the tones is slightly shorter than the rest.  The subject’s task is to detect the shorter tones.  The following percentages of correct detections were observed:

Normal

Sleep

Sleep-Deprived

for 24 Hours

Sleep-Deprived

for 48 Hours

85

83

76

64

75

60

58

76

52

63

60

48

38

47

50

What do you conclude, using α = 0.05.

If you choose to type the data into the Data Editor, name the variables, “Group” and “Pct_Corr.”  The saved data file for this problem is “Ch15prob1.”

SOLUTION

Step 1:  Enter and Name the Data.  As usual, you have three choices for entering the data: 1) by typing the scores directly into the Data Editor; 2) by downloading from the web the saved data file for this example, and 3) by opening the saved data file (for this example) that resides on your computer. 

Entering the scores by typing them directly into the Data Editor.  If you choose to type in the data, remember to name the grouping variable Group and the other variable Pct_Corr.  If you have any questions, please follow the instructions in Illustrative Example 1 for Chapter 15, substituting the variables and scores for this problem.

Entering the scores by downloading from the web, the saved data file for this example.  To enter the scores using this option, click here, and then click Open from the drop-down menu.  

Entering the scores by opening the saved data file (for this example) that resides on your computer.   If you choose to open the saved data file, the name of the file is Ch15prob1.  To enter the data and name the variables for this problem, please follow the instructions in Illustrative Example 1 for Chapter 15.

When the data are entered and named correctly, the Data Editor, Data View should look like Figure 15.1.1.

Figure 15.1.1.  Data Editor with Group and Pct_Corr scores entered.

Step 2:  Conclusion Regarding the Overall Effect of the Independent Variable, using α = 0.05.  The appropriate test to evaluate the overall effect of the independent variable is the One-Way Analysis of Variance.  To have SPSS do the analysis using this test,  

Click Analyze.

Select Compare Means.

Click One-Way ANOVA….

Click the ► button for the Factor:box.

Click Pct_Corr in the large box on the left.

Click the ► button for the Dependent List: box.

Click the Options button.

Click Descriptive.

Click Continue

Click OK.

This produces a drop-down menu.

This also produces a drop-down menu.

This produces the One-Way ANOVA dialog box with Group highlighted. 

This moves Group into the Factor: box.

This highlights Pct_Corr.

This moves Pct_Corr into the Dependent List:  box.  

This produces the One-Way ANOVA: Optionsdialog box.  

This puts a P in the Descriptive box, telling SPSS to compute some descriptive statistics and include them in the output.

This returns you to the One-Way ANOVA dialog box.

SPSS analyzes the Stress data and outputs the results to the Viewer.  The output is shown below in Figure 15.1.2.

Figure 15.1.2.  Results of One-Way ANOVA analysis.

The SPSS viewer shows two tables, the Descriptives table and the ANOVA table.  The ANOVA table is the table we use to conclude about the overall effect of the independent variable.  This table shows that Fobt = 14.062 and the obtained probability (Sig.) is .001.  Since .001 < 0.05, your conclusion is to reject H0.  Sleep deprivation appears to affect sustained attention.  Sure beats doing this by hand!!

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