In a 1994 study, 164 pregnant, HIV-positive women were randomly assigned to receive the drug AZT during pregnancy and 160 such women were randomly assigned to a control group that received a placebo. It turned out that 40 of the mothers in the control group gave birth to babies who were HIV-positive, compared to only 13 in the AZT group.
a. Is this an observational study or an experiment?
b. Identify the explanatory and response variables.
c. Produce a 2 × 2 table of counts, with the explanatory variable in columns.
d. Calculate the proportion of babies who were born HIV-positive in each group.
e. Calculate the relative risk of a baby being born HIV positive, comparing those in the placebo group to those in the AZT group.
f. Produce a segmented bar graph to display these data.
g. Summarize what these data reveal about the question of whether AZT is effective for reducing the HIV-positive proportion of newborn babies?