Problem 7.41 The following data are from Charles Darwin’s study of cross- and self[1]fertilization. Pairs of seedlings of the same age, one produced by cross-fertilization and the other by self-fertilization, were grown together so that members of each pair were grown under nearly identical conditions. The data represent the final heights of the plants after a fixed period of time.

(a) Compute a 95% confidence interval for the difference in the mean heights. State your model assumptions.

(b) Compute a 99% confidence interval for the difference in the mean heights. Pair Cross- Self[1]fertilized fertilized 1 23.5 17.4 2 12.0 20.4 3 21.0 20.0 4 22.0 20.0 5 19.1 18.4 6 21.5 18.6 7 22.1 18.6 8 20.4 15.3 9 18.3 16.5 10 21.6 18.0 11 23.3 16.3 12 21.0 18.0 13 22.1 12.8 14 23.0 15.5 15 12.0 18.0