One thing I don't follow - how is the value of 18 arrived at? Is it a nice integer chosen somewhat arbitrarily for teaching purposes? Or is the use of an integer biologically or statistically useful in a way that this video does not cover? Thanks y'all.

you keep saying that its okay that the data are not normally distributed, but the majority on internet say that the data HAS to be. Im so freakin confused, I wouldve have used the sign test but alot dont recommended it either so what is left/which test can be applied for a one sample ordinal data?