How long do you have to wait for more than one thing to happen?

They are incredibly useful, but what exactly are they?

How long do you have to wait for something to happen?

What's the chance that something happens?

Measuring your chance of success.

To work out the famous R number you need to know the time between infections.

How long does it take for one person to infect another?

The doubling time for the Omicron variant seems to be scarily fast. But how do you calculate it?

What's a quality adjusted life year, or QALY?

Can you capture people's behaviour in epidemiological models?

How does a smooth flow suddenly become turbulent? The Reynolds number helps understand the transition.