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. Author manuscript; available in PMC: 2018 Jul 7.
Published in final edited form as: Lancet HIV. 2018 Jun;5(6):e329–e334. doi: 10.1016/S2352-3018(18)30045-6

Table 3. Examples illustrating the rate ratio (RR) and the averted infections ratio (AIR) for hypothetical trials of prophylactic agents.

Trial Incidence rate (# events) RR (90% CI) Incidence rate, hypothetical placebo arm AIR (90% CI)
Experimental agent Active control (TDF-FTC)
A 2 (40) 2 (40) 1.0 (0.69, 1.44) 5 1.0 (0.78, 1.28)
B 2 (40) 2 (40) 1.0 (0.69, 1.44) 2 ND
C 2 (40) 2 (40) 1.0 (0.69, 1.44) 5 1.0 (0.78, 1.28)
D 1 (20) 1 (20) 1.0 (0.59, 1.68) 5 1.0 (0.88, 1.14)
E 2 (40) 1 (20) 2.0 (1.27, 3.14) 2 0.0 (ND)
F 2 (40) 1 (20) 2.0 (1.27, 3.14) 5 0.75 (0.62, 0.91)

2000 person-years follow-up in experimental and active control arms in all trials.

Incidence rates expressed per 100 person-years.

Hypothetical placebo arm rate assumed to be known in derivation of CI for the AIR ND, not defined