Astent is a metal mesh cylinder that holds a coronary artery open after a blockage has been removed. However, in many patients the stents, which are made from bare metal, become blocked as well. One cause of the reoccurrence of blockages is the body’s rejection of the foreign object. In a study published in the New England Journal of Medicine (January 2004), a new polymer-based stent was tested.

After insertion, the new stents slowly release a drug (paclitaxel) to prevent the rejection problem. A sample was recruited of 1,314 patients, who were receiving a stent in a single, previously untreated coronary artery blockage. A total of 652 were randomly assigned to receive a bare-metal stent, and 662 to receive an identical-looking polymer drug-releasing stent. The results were recorded in the following way:

Column 1: Patient identification number

Column 2: Stent type (1 = bare metal, 2 = polymer based)

Column 3: Reference-vessel diameter (the diameter of the artery that is blocked, in millimeters)

Column 4: lesion length (the length of the blockage, in millimeters)

Reference-vessel diameters and lesion lengths were measured before the stents were inserted.

The following data were recorded 12 months after the stents were inserted.

Column 5: Blockage reoccurrence after 9 months (2 = yes, 1 = no)

Column 6: Blockage that needed to be reopened (2 = yes, 1 = no)

Column 7: Death from cardiac causes (2 = yes, 1 = no)

Column 8: Stroke caused by stent (2 = yes, 1 = no)

a. Using the variables stored in columns 3 through 8, determine whether there is enough evidence to infer that the polymer-based stent is superior to the bare-metal stent.

b. As a laboratory researcher in the pharmaceutical company write a report that describes this experiment and the results.