Absolute risk reduction is the decrease in the number affected per number exposed:

(15-5)/50 = 10/50 = 0.2

FA 2020 PG 258

Absolute risk reduction BY DEFINITION : The difference in risk (not the proportion) attributable to the intervention as compared to a control.

ARR = (c/c + d ) - ( a/ a + b )

I assumed c+d as 50 for azithromycin and a+b as 50 for erythromycin

= 15/50- 5/50 = .3 -.1 = .2

in FA the example is If 8% of people who receive a placebo vaccine develop the flu vs 2% of people who receive a flu vaccine, then ARR = 8%–2% = 6% = 0.06.