Volunteer patients were randomized into one of two experiment groups where they would receive an experimental vaccine or a placebo. They were subsequently exposed to a drug-sensitive strain of malaria and observed to see whether they came down with an infection.
Format
A data frame with 20 observations on the following 2 variables.
- treatment
Whether a person was given the experimental
vaccineor aplacebo.- outcome
Whether the person got an
infectionorno infection.
Source
Lyke et al. 2017. PfSPZ vaccine induces strain-transcending T cells and durable protection against heterologous controlled human malaria infection. PNAS 114(10):2711-2716. doi:10.1073/pnas.1615324114 .
Details
In this study, volunteer patients were randomized into one of two experiment groups: 14 patients received an experimental vaccine or 6 patients received a placebo vaccine. Nineteen weeks later, all 20 patients were exposed to a drug-sensitive malaria virus strain; the motivation of using a drug-sensitive strain of virus here is for ethical considerations, allowing any infections to be treated effectively.
Examples
library(dplyr)
# Calculate conditional probabilities of infection after vaccine/placebo
malaria %>%
count(treatment, outcome) %>%
group_by(treatment) %>%
mutate(prop = n / sum(n))
#> # A tibble: 3 × 4
#> # Groups: treatment [2]
#> treatment outcome n prop
#> <fct> <fct> <int> <dbl>
#> 1 placebo infection 6 1
#> 2 vaccine infection 5 0.357
#> 3 vaccine no infection 9 0.643
# Fisher's exact text
fisher.test(table(malaria))
#>
#> Fisher's Exact Test for Count Data
#>
#> data: table(malaria)
#> p-value = 0.01409
#> alternative hypothesis: true odds ratio is not equal to 1
#> 95 percent confidence interval:
#> 1.338381 Inf
#> sample estimates:
#> odds ratio
#> Inf
#>