"Tight glycemic control" means that the blood sugar is kept within a narrow range. Read the abstract below, and then answer the questions that follow it. "Methods: In this two-center, prospective, randomized trial, we enrolled 980 children, 0 to 36 months of age, undergoing surgery with cardiopulmonary bypass. Patients were randomly assigned to either tight glycemic control . . . targeting a blood glucose level of 80 to 110 mg per deciliter . . . or standard care in the cardiac intensive care unit.
a. Identify the treatment variable and the response variable.
b. Was this a controlled experiment or an observational study? Explain.
c. What does the p-value show?
d. Can you conclude that the use of tight glycemic control affects the rate of infections? Why or why not?