sec 17.2 has some issues

[murphyk]

In sec 17.2.1 (rank test), the calculation (1+200)/2 = 100.5 might seem obscure to some.
Later you write this more clearly as shown below. Maybe move here?

In sec 17.2.2(vaccines), the pargraph below is hard to understand

The numbers in table 17.1 are obscure - where does 293 come from? (I assume it's ceil(585/2), but this needs to be explained.)

Finally you say that the multivariate hypergeometric distribution is explained in ch 3, but that only covers the univariate case, IIUC. So the code may not be very clear to some readers.