Question

1. Angioplasty is a surgical procedure to restore blood flow through narrow or blocked arteries. More than a million heart patients undergo this procedure every year. A recent study of 1,256 heart patients assessed the benefits of angioplasty. In this study, all patients had substantial blockage of their arteries and were being treated with medication such as aspirin and beta-blockers. The researchers randomly assigned half of the patients to receive angioplasty. The other half did not receive the surgical procedure. After 10 years, the researchers compared the heart attack rates for the two groups.  The results of this study were statistically significant, such that patients who received the surgical procedural were significantly less likely to have a heart attack over the following ten years (p < .05).

In terms of making a causal inference about the relationship between angioplasty and heart attacks, which of the following is true:

The researchers can draw strong causal inferences because the two groups have an equal number of people in them

The researchers can draw strong causal inferences because participants were randomly assigned to treatment and control conditions

The researchers cannot draw strong causal inferences because patients were not randomly selected into the study

The researchers cannot draw strong causal inferences because there is no control group

2. Yancy, a Walton College of Business graduate, wants to start a hot dog stand on Dickson Street.   He needs to raise $15,000 for start-up supplies and equipment. He believes that in order to be successful, he would need to sell more than 300 hot dogs on average per night. He creates a survey and stands on Dickson Street asking people to state whether or not they would buy a hot dog. He notices that the demand increases significantly after midnight. Sixty people complete his survey and based on their feedback, he purchases the supplies and equipment. He opened his stand and after the first two weeks he wants to analyze his sales. He is open 5 days a week and finds the average number of hot dogs sold is 335 with a standard deviation of 50. Is he meeting his original goal to be successful? Assume a 5% level of significance for this question.

The critical value is _________?

1.833

-1.833

1.671

-1.671

Answer 1

Answer for Question 1 ) The researchers can draw strong causal inferences because participants were randomly assigned to treatment and control conditions

Answer for Question 2) 1.671