Exercises: Measures of occurrence & association

Why might it be difficult to accurately calculate the risk of dying from bladder cancer over a 10-year period for a population of 5 million people alive at the beginning of the period? (Choose the best answer.)

An observational study found that 650 of 28,000 patients who took a new antibiotic, compared to 450 of 32,000 patients who took an existing antibiotic, developed a cardiac arrhythmia during 1 year of follow-up. Which of the following is an estimate of the risk ratio, showing the association between the new antibiotic and increased risk of cardiac arrhythmia?

In a cohort study, researchers found that 2,300 of 77,300 patients taking a new arthritis drug suffered a heart attack, while 1,600 of 91,600 patients taking an existing drug had a heart attack. Total follow-up time was 127,545 person-years for patients taking the new drug and 169,460 for patients taking the old drug. Which of the following is an estimate of the rate ratio, showing the association between the new drug and heart attack?