E81 Lead is toxic , particularly for young children , and for this reason government regulations severely restrict the amount of lead in our environment. But this was not always the case. In the early part of the 20th century, the underground water pipes in many US. cities contained lead, and lead from these pipes leached into drinking water. In this exercise you will investigate the effect of these lead water pipes on infant mortality using the dataset, lead imortality .dta , which contains data on infant mortality, type ofwater pipes (lead or nonlead), water acidity (pH), and several demographic variables for 172 US cities in 1900 ; see also Lead _Mortality _Description .pdf. (a) Compute the average infant mortality rate, infrate ,for cities with lead pipes and for cities with non lead pipes . Is there a statistically signicant difference in the average ? (b) The amount of lead leached from lead pipes depends on the chemistry of the water running through the pipes . The more acidic the water (that is, the lower its pH), the more lead is leached Run a regression of irritate on lead , ph, and the interaction term lead >