As part of a larger study, Stipanicic, Nolin, Fortin, and Gobeil (2008) compared global IQ scores in a sample of 11 children (n1 = 11) with shaken baby syndrome (SBS) to those of 11 children without the syndrome (n2 = 11). Global IQ scores were 86.36 ± 15.16 (M ± SD) for children with SBS and 104.09 ± 12.10 (M ± SD) for children without SBS.

(a) Test whether or not mean scores differed between groups, using a .05 level of significance. State the value of the test statistic and the decision to retain or reject the null hypothesis.

(b) Compute effect size using estimated Cohen's d.

(c) Compute effect size using eta-squared.