Prostate Cancer Treatment

The following portion of an abstract gives information on the comparison of treatments of men with prostate cancer.

Read it and answer the questions about it below. The prostate gland surrounds the neck of the bladder in men. "Methods: Between 1989 and 1999, we randomly assigned 695 men with early prostate cancer to watchful waiting or radical prostatectomy and followed them through the end of 2012.

The primary end points in the Scandinavian Prostate Cancer Group Study Number 4 (SPCG-4) were death from any cause, death from prostate cancer, and the risk of metastases.

Results: During 23.2 years of follow-up, 200 of 347 men in the surgery group and 247 of the 348 men in the watchfulwaiting group died. Of the deaths, 63 in the surgery group and 99 in the watchful-waiting group were due to prostate cancer; the relative risk was 0.56 (95% confidence interval, 0.41 to 0.77; P = 0.001), and the absolute difference was 11.0 percentage points (95% CI, 4.5 to 17.5). The number needed to treat to prevent one death was 8. One man died after surgery in the radical-prostatectomy group. . . .

The benefit of surgery with respect to death from prostate cancer was largest in men younger than 65 years of age (relative risk, 0.45) and in those with intermediate-risk prostate cancer (relative risk, 0.38).

However, radical prostatectomy was associated with a reduced risk of metastases among older men (relative risk, 0.68; P = 0.04)." (Source: Anna Bill-Axelson et al. 2014. Radical prostatectomy or watchful waiting in early prostate cancer. New England Journal of Medicine 370, 932-942.)

a. Compare the percentages of death for the two groups descriptively. Which group had patients who were more likely to live?

b. Find and compare the percentage who died from prostate cancer for each group.

c. Was this an observational study or a controlled experiment?