A Step by Step Guide for SPSS and Exercise Studies

68 Statistical tests
Table 18
Sometimes, the sign of the t value is negative. This does not mean that your
analysis is wrong. It simply signifies that the mean of the second group is higher
than the mean of the first group. In Table 19, the t value was positive because the
first group had a higher mean than the second group.
In the various statistical texts you will frequently come across the terms ‘onetailed’
and ‘two-tailed’ t tests. The one-tailed test is used when two groups are
expected to differ in a particular direction. For example, elite athletes are
predicted to have higher take-off velocity compared to non-elite ones. In other
cases, such as the one presented here, you may not have a clear hypothesis
regarding the direction of the difference. Therefore, you need to use a two-tailed
t test. SPSS provides the two-tailed significance values only. To obtain the onetailed
significance values you need to consult a table of critical t values which is
located at the end of most statistical texts.
How to report the test
When you present the results of a t test you need to report the means and
standard deviations of the two groups (club A/club B), the Levene test and its
significance level, as well as the t value, its degrees of freedom (df), and
significance level. Example 1 shows how you could report the results of a t test
in a table.
Example 1: Differences in take-off velocity between long-jumpers from Clubs A
and B
M (SD) t df
Take-off velocity of high jumpers fom Club A 9.63 (.52) 9.96** 18
Take-off velocity of high jumpers fom Club B 7.49 (.43)
** p