In 2004, an article was published that summarized a retrospective (i.e. looking back at data in the past) study regarding the effectiveness of Ribavirin in treating Severe Acute Respiratory Syndrome (SARS). The study looked at 229 cases of SARS from the past and observed whether the patient was treated with Ribavirin and whether the patient died.

1. What is the population of interest in this retrospective study?
2. What are the two variables that were relevant for each SARS patient?
3. Propose another variable that would result in measurement data from each SARS patient.
4. The study found that 12.9% of the SARS patients who were not treated with Ribavirin died, while only 10.3% of the SARS patients who were treated with Ribavirin died. Assuming that this difference is "significant," can the cause of that difference be attributed to Ribavirin? Explain your answer.