A Step by Step Guide for SPSS and Exercise Studies

66 Statistical tests
How to carry out the test
In the example shown in Dialog box 63, move the dependent variable that will
serve as a measure of comparison (i.e., velocity) into the Test Variable(s) box. If
you want to perform more than one t test using different dependent variables,
move all the dependent variables into this box.
The grouping (independent) variable is club. You should already have in the
data file a variable called club which has assigned different codes to different
clubs (e.g., code 1 to participants from club A and code 2 to participants from
club B). Variable coding is essential; otherwise, you will not be able to carry out
the independent samples t test (Figure 21).
If the grouping variable is continuous (e.g., strength, time), you need to
dichotomise it by identifying a Cut point. This cut-off point could be the median
value of the variable that will split the scores into 2 groups (see Compute in the
Transform menu to compute a new categorical variable that will contain the
codes for the two new groups). Click Continue and then OK (Dialog box 64).
Table 18 presents the sample size, mean, standard deviation, and standard
error of the mean (i.e., amount of error in the prediction of the population mean)
in each group. The statistical comparison of the group means is performed in
Table 19. If the Levene test is significant, you should conclude that the variances
of the take-off velocity scores in the two groups are not homogeneous. In this
case, you should report the t value that corresponds to the equal variances not
assumed. If the Levene test is not significant, you should conclude that the
variances are homogeneous and you should report the t value that corresponds to
the equal variances assumed. 1
The Levene test in Table 18 is not significant (F ˆ .81; p ˆ .38, which is
greater than .05), and the corresponding t value is significant (t ˆ 9.96; p ˆ .000).
Therefore, you should conclude that the mean scores of take-off velocity differ
Dialog box 63
1 In Table 19 both tests give the same result, but this is not always the case.