Question

research suggests that identical twins have many similarities, such as body weights, even as adults. a sample of ten sets of identical twins were weighed and had their weights recorded in kilograms. the researcher wishes to test whether there is a statistically significant difference in adult weight between first - born and second - born identical twins. source: m. j. tramo, w. c. lodtus, t. a. stukel, r. l. green, j. b. weaver, and m. s. gazzaniga. “brain size, head size, and intelligence quotient in monozygotic twins.” neurology 50, 1246 - 52. given the design of the study and the question of interest, which one of the following computer outputs is relevant to use? a. paired t - test and cl sample n mean stdev se mean first - born 10 77.59 23.38 7.39 second - born 10 78.02 17.36 5.49 difference 10 - 0.43 11.83 3.74 95% upper bound for mean difference: 6.43 t - test of mean difference = 0 (vs < 0): t - value = - 0.12 p - value = 0.455 b. two - sample t - test and cl sample n mean stdev se mean first - born 10 77.6 23.4 7.4 second - born 10 78.0 17.4 5.5 difference = mu (first - born) - mu (second - born) estimate for difference: - 0.43 95% upper bound for difference: 15.64 t - test of difference = 0 (vs <): t - value = - 0.05 p - value = 0.482 df = 16

Explanation:

Since we are dealing with identical twins (paired data), a paired - t test is appropriate. A paired - t test is used when we have two related samples (in this case, first - born and second - born twins from the same set). A two - sample t test is used for two independent samples.

Answer:

A. Paired T - Test and CI