Question

A study was conducted in men aged 40-70 in order to determine whether exercising for 2 or more hours per week decreases the likelihood of heart attack. The cases were 1,000 men who had recently had a heart attack; of these, 236 reported that they had regularly exercised for two or more hours per week prior to their heart attack. 1,000 controls were also selected for the study; of these, 379 reported that they exercised regularly. Calculate the magnitude of association between regular exercise and heart attack. What does your calculation suggest? (Select one answer.) A. People who exercise regularly have about 0.5 times the risk of having a heart attack compared to people who don't exercise. B. People who exercise regularly have about 2.0 times the risk of having a heart attack compared to people who don't exercise. C. People who exercise regularly have about a 50% chance of having a heart attack.

Answer 1

Answer: alternative A.

Explanation: In this case, we will consider people that already have had a heart attack. In this specific group of 1,000 people, 236 exercised regularly and had gone through this situation.

We can infer that 23.6% of people who exercised regularly have experienced that by dividing 236/1,000= 0.236= 23.6%.

If 236 people exercised, 1,000-236=764 didn't exercise regularly prior to their heart attacks, so 74.6% were considered to be sedentary.

If there's 0.236 chance out of 1 to exercise and still have a heart attack compared to 0.764 out of 1 to be sedentary and have the same experience, we can divide both ratios to compare them, so 0.236/0.764= 0.3089.

Alternative A claims that people who exercise have around 0.5 chance of having heart attacks compared to people who don't. Since our ratio resulted in 0.3089, we consider this number the closest to 0.5. Alternative B is absurd because in order for people who exercise to have 2x the risk compared to people who don't, the number of people who exercised and went through that must be 2x bigger than people who didn't. Alternative C doesn't apply as well, because we already verified that the chance people who exercise have a heart attack equal to 23,6%.