The following table shows the average number of words understood by later-born and first-born one-year-old children from two random samples. Assume the population variances of the number of words understood are equal.

Later-Born First-Born Sample mean 430.2 552.0 Sample standard deviation 130.8 133.7 Sample size 12 12

a. Construct a 98% confidence interval to estimate the difference between the average number of words understood by first-born and later-born one-year-old children.

b. What conclusions can be made about the difference between the two populations?

c. What assumptions need to be made in order to perform this procedure?

AppendixLO1