I want to start with some data and a model from outside biology. The “data” (such as it is) comes from a Dilbert cartoon, and the competing hypotheses about the data come from Dilbert (the hard-working and long-suffering engineer) and his boss (the evil pointy-haired boss). We will work through a statistical test to show that Dilbert is right and the boss is wrong — of course!

In this cartoon, Dilbert’s evil pointy-haired boss decides he’s found a new way that employees are cheating him: they are taking fake “sick days” on Mondays and Fridays in order to get longer weekends. His proof? The fact that 40% of sick days fall on a Monday or Friday.

Before we get into statistics, take a moment to think about the situation…

### What proportion of sick days ‘should’ fall on Monday or Friday (assuming there is no bias to when people get sick, and no one is abusing their sick days?)