Note:  the $\displaystyle {r}^{{2}}$ effect size for two-sample independent-measures t-test is the same thing as the $\displaystyle \eta^{{2}}$ effect size for ANOVAs.  Again, SPSS does not calculate this for us.  However, this time you can calculate the value with much less computational effort using the ANOVA summary table.

	SS	df	MS	F-ratio	sign.
Between	65	2	2.71	$\displaystyle {F}={1.512}$	$\displaystyle {p}={0.241}$
Within	43	24	1.79
TOTAL	108	26

$\displaystyle \eta^{{2}}=\frac{{{S}{S}_{\text{between}}}}{{{S}{S}_{\text{total}}}}=$