Problem: Keepem Living Hospital reports a mortality rate of 3% at the end of a 6-month follow-up on a new procedure. Heavenly Hospital reports a 22% mortality rate for the same procedure during the same 6-month period. Which of the following could be confounding factors that should be examined? a. How sick the patients were (disease severity) prior to undergoing the procedure. b. Differences in the care the patient received after the procedure. c. Differences in data collection standards and definitions. For example were patients included only while hospitalized? If tracking occurred after discharge how diligently were the patients tracked? d. All of the above.