Have you heard that water spins down the plughole in opposite directions depending on whether you’re in the northern or southern hemisphere? It’s all because of the Coriolis effect —

the rotation of the earth. In the northern hemisphere the water spins down the drain clockwise, and in the southern hemisphere it spins anticlockwise. Well, maybe. Notwithstanding much disagreement, many scientists reason that the effect is so small that it won’t be seen in a regular handbasin or toilet, as it will be swamped by the influence of inevitable asymmetries in the shape of the bowl.

It would be easier if you had a toilet the size of Australia.

Suppose you decide to investigate for yourself. You can try out the rotation from wherever you happen to be in the world. Use as many different sinks as you can find, of different designs,

to try to compensate for the possibility of asymmetric flaws in each sink.
Let’s say you conduct 50 careful trials in different sinks, and you find that the water spins down the drain in the direction predicted by the Coriolis effect in 34 of your trials.
Follow the steps laid out in Exercise 32.10 to test your evidence for a systematic spin bias in your location. Decide upon appropriate hypotheses, sketch the null distribution and the area represented by the P-value, calculate the P-value, and interpret your findings. Is this study design a reasonable way of investigating the question?