Intraaortic balloon counterpulsation (IABP) has been used to attempt to reduce the rate of deaths in people who have had heart attacks that are complicated by cardiogenic shock. In this treatment, a balloon that pulsates is inserted into the aorta. A randomized study showed that 119 out of 300 patients assigned to IABP died within 30 days and that 123 out of 298 assigned to the control group (no IABP) died within 30 days.
a. Was this an observational study or a controlled experiment? Explain.
b. Which sample did better, the sample assigned to IABP or the sample with no IABP? If you perform an hypothesis test with a two-sided alternative, the p-value is 0.689.
c. Choose the correct conclusion:
i. We have shown that IABP has no effect on the death rate.
ii. We have not shown that IABP affects the death rate.
d. Explain your choice for part c.