Question

2. A researcher believes that special early training will improve IQ. She identifies 7 pairs of identical twins and, when the infants are 3 years old, she randomly assigns one twin in each pair to special training. The other twin receives no special training. Each twin is tested on IQ at age 4. Test whether the two groups differ. The data are given below:

Pair number:        1     2        3        4          5          6          7

Training              114   110      111      120      112      113      118 (Group 1)

No training         107   105      104      109      103      105      108 (Group 2)

a. State the null and alternative hypotheses.

b. Make a diagram of the regions of acceptance and rejection associated with the null hypothesis. Use alpha = .01, one-tailed.

c. Calculate the value of the t-statistic for this test. Use the direct difference method because the samples are correlated.

d. Do you reject or accept the null hypothesis? On what basis (what's the decision rule?) and what does it mean?

Answer 1