Statistics for the Behavioral Sciences by Frederick J. Gravetter, Larry B. Wallnau ISBN 10: 1305504917 ISBN 13: 9781305504912

SPSS ® 437
5. When the obtained F-ratio is significant (that is, H 0
is
rejected), it indicates that a significant difference lies
between at least two of the treatment conditions. To
determine exactly where the difference lies, post hoc
comparisons may be made. Post hoc tests, such
as Tukey’s HSD, use MS error
and df error
rather than
MS within treatments
and df within treatments
.
6. A repeated-measures ANOVA eliminates the influence
of individual differences from the analysis. If
individual differences are extremely large, a treatment
effect might be masked in an independent-measures
experiment. In this case, a repeated-measures
design might be a more sensitive test for a treatment
effect.
KEY TERMS
individual differences (417)
between-treatments variance (417)
between-subjects variability (420) error variance (421)
SPSS ®
General instructions for using SPSS are presented in Appendix D. Following are detailed
instructions for using SPSS to perform the Single-Factor, Repeated-Measures Analysis of
Variance (ANOVA) presented in this chapter.
Data Entry
1. Enter the scores for each treatment condition in a separate column, with the scores for
each individual in the same row. All the scores for the first treatment go in the VAR00001
column, the second treatment scores in the VAR00002 column, and so on.
Data Analysis
1. Click Analyze on the tool bar, select General Linear Model, and click on
Repeated-Measures.
2. SPSS will present a box titled Repeated-Measures Define Factors. Within the box, the
Within-Subjects Factor Name should already contain Factor 1. If not, type in Factor 1.
3. Enter the Number of levels (number of different treatment conditions) in the next box.
4. Click on Add.
5. Click Define.
6. One by one, move the column labels for your treatment conditions into the Within
Subjects Variables box. (Highlight the column label on the left and click the arrow to
move it into the box.)
7. If you want descriptive statistics for each treatment, click on the Options box, select
Descriptives, and click Continue.
8. Click OK.
SPSS Output
We used the SPSS program to analyze the data from Example 13.1 comparing three strategies
for studying before an exam. Portions of the program output are shown in Figure 13.4. Note
that large portions of the SPSS output are not relevant for our purposes and are not included.
The first item of interest is the table of Descriptive Statistics, which presents the mean,
standard deviation, and number of scores for each treatment. Next, we skip to the table showing
Tests of Within-Subjects Effects. The top line of the factor1 box (Sphericity Assumed)
shows the between-treatments sum of squares, degrees of freedom, and mean square that
form the numerator of the F-ratio. The same line reports the value of the F-ratio and the level
of significance (the p value or alpha level). Similarly, the top line of the Error (factor1) box
shows the sum of squares, the degrees of freedom, and the mean square for the error term (the