To investigate whether giving chest-compression-only (CC) instructions rather than standard cardiopulmonary resuscitation (CPR) instructions to the witness of a heart attack will improve the victim€™s chance of surviving, researchers Hupfl et al. (Th e Lancet, 2010) combined the results from three randomized experiments. In each experiment, the emergency services dispatcher randomly assigned either CC or CPR instructions to the bystander who was at the site where a person had just experienced a heart attack. They found that of the 1,500 cases where CC instructions had been given, 211 people had survived, whereas of the 1,531 cases where standard CPR instructions had been given, the number was 178. Here are the data organized in a 2 × 2 table:

a. Identify the observational units. Choose one.
A. Whether given CC or CPR instructions
B. Whether heart attack victim survived or not
C. Cases of heart attacks where emergency services were contacted
D. Those people who survived

b. What is the primary purpose of random assignment in this type of study? Choose one.
A. To ensure that subjects are representative of the population of interest
B. To ensure that the groups are of equal sizes
C. To create treatment groups that are alike in all aspects except for the treatment administered
D. To improve accuracy of results

c. Identify the explanatory variable. Choose one.

A. Whether given CC or CPR instructions
B. Whether heart attack victim survived or not
C. Cases of heart attacks where emergency services were contacted
D. Those people who survived

d. Identify the response variable. Choose one.
A. Whether given CC or CPR instructions
B. Whether heart attack victim survived or not
C. Cases of heart attacks where emergency services were contacted
D. Those people who survived

e. The explanatory variable is ________ (categorical/quantitative).
f. Th e response variable is ________ (categorical/quantitative).
g. In this context, which of the following is an (are) appropriate statistic value(s)? Choose all that apply.

A. 211/1,500 ˆ’ 178/1,531 = 0.024
B. 211/3,031 ˆ’ 178/3,031 = 0.011
C. 211/389 ˆ’ 178/389 = 0.085
D. (211/1,500)/(178/1,531) = 1.21

h. Give two possible explanations for the observed statistic value(s) as selected in part (g).

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Total CPR 178 211 389 Yes Survived? 1,353 1,289 2,642 No Total 1,531 3,031 1,500