A psychologist is examining the influence of an older sibling in the development of social skills. A sample of 24 three year old children is obtained. Half of these children had no siblings and the others had at least one older sibling who is within 5 years of the child's age. The psychologist records a social skills score for each child and obtained the following data:
No Sibling.....................Older Sibling
...n=12...............................n=12
...M=17..............................M=24
...SS=580........................SS=608
Do these data indicate that having an older sibling has a significant effect on the development of social skills? Use a two tailed test at the 0.05 level.