[teraflop]

If 22% of patients in the placebo group died, and 12% in the test group, then that's a reduction of 1 - (12/22) = 45% in the risk of death over that time interval.

The true value could easily be 51% if the percentages reported in the Guardian were rounded.

[cjbgkagh]

You could subtract both percentages by the baseline average risk of death for 5 years at the age group that people are most likely to get this type of cancer.