Question 1 1 . A hypothetical HIV vaccine trial involving 20. 000 participants - 10 . 000 in the vaccine group and 10 . 000 in the placebo group- had the following results : 6.3 infections per 1000 in the vaccine group and 9 . 0 infections per 1000 in the placebo group . I ran a computer simulation to predict possible outcome omes of the trial if the null hypothesis is true - that is , if vaccinated and unvaccinated people are equally likely to contract HIV . I ran over 1000 virtual trials of 20 . 000 people ( 10. 000 per group ) assuming that the vaccine is ineffective . Outcomes are expressed as excess infections in the placebo group . Here are the results of the 1000 virtual trials displayed as a histogram . 401 - 35 - 30 - 25 - Count : 20 - 15 - 10 - - 45- 42 - 39 - 35 -33- 30 - 37 - 24 - 21 - 18 - 15 -12 - 9 - 6 - 3 0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 Excess infections in the placebio group*