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. (The 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 x 2 table:

CC CPR Total
Yes 211 178 389
Suvived No 1289 1353 2642
Total 1500 1531 3031

1. The explanatory variable is (Choose one):

a. categorical
b. quantitative

2. The response variable is (Choose one):

a. categorical
b. quantitative

3. In this context, which of the following is an (are) appropriate statistic value(s)? Choose all that apply:

a. 211/1,500 - 178/1,531 = 0.024
b. 211/3,031 - 178/3,031 = 0.011
c. 211/389 - 178/389 = 0.085
d. (211/1,500) / (178/1,531) - 1.21

4. Give two possible explanations for the observed statistic value(s) as selected in part 3.