Say we want to use a method that requires $n > 30$. (Whether this refers to number of observational units or total observations is sometimes vague.)
We have observations on 10 patients for four time points ($t$). Consequently, we have $n=10$ but $t \cdot n = 40$ observations.
Do we consider the required minimum $n$ for the method met due to the total number of observations or not due to the number of observational units?
Although this is really basic, I have not come across a relevant description of this and wonder if anyone have references to this topic.