Researchers conducted a prospective cohort study in which male patients who had an out-of-hospital cardiac arrest were submitted to therapeutic hypothermia (intravenous infusion of cold saline followed by surface cooling with the goal of maintaining body temperature of 33 degrees Celsius for 24 hours. Note that normal body temperature is 37 degrees Celsius). The survival status, length of stay in the intensive care unit (ICU), and time spent on a ventilator were measured. Each of these variables was compared to a historical cohort of patients who were treated prior to the availability of therapeutic hypothermia. Of the 52 hypothermia patients, 37 survived; of the 74 patients in the control group, 43 survived. The median length of stay among survivors for the hypothermia patients was 14 days versus 21 days for the control group. The time on the ventilator among survivors for the hypothermia group was 219 hours versus 328 hours for the control group. Source: Storem, Christian, et al. Mild Therapeutic Hypothermia Shortens Intensive Care Unit Stay of Survivors After Out-of-Hospital Cardiac Arrest Compared to Historical Controls. Critical Care 2008, 12:R78 BioMed Central

(a) What does it mean to say this is a prospective cohort study?

(b) What is the explanatory variable in the study? Is it qualitative or quantitative?

(c) What are the three response variables in the study? For each, state whether the variable is qualitative or quantitative.

(d) Is time on the ventilator a statistic or parameter? Explain.

(e) To what population does this study apply?

(f) Based on the results of this study, what is the probability a randomly selected male who has an out-of-hospital cardiac arrest and submits to therapeutic hypothermia will survive? What about those who do not submit to therapeutic hypothermia?