Chapter 6, Problem 67P

We have previously described Data Set LEAD.DAT (at www.cengagebrain.com), in which children were classified according to blood-lead level in 1972 and 1973 by the variable lead_grp, where 1 = blood-lead level < 40 μg/100 mL in both 1972 and 1973, 2 = blood-lead level ≥ 40 μg/100 mL in 1973, 3 = blood-lead level ≥ 40 μg/100 mL in 1972 but < 40 μg/100 mL in 1973.

Compute the mean, standard deviation, standard error, and 95% CI for the mean verbal IQ for children with specific values of the variable lead_grp. Provide a box plot comparing the distribution of verbal IQ for subjects with lead_grp = 1, 2, and 3. Summarize your findings concisely.