Debate: fixed vs. random block effects
Ex: does it make sense to view the 4 specific rows blocked by elevation as randomly selected from a larger population?
Ex: 4 dosages of a new drug are randomly assigned to 4 mice in each of the 20 litters: RCBD with a = 4 dosage treatments and b = 20 litters, for a total of ab = 80 observations. Here, blocks (litters) can be considered as random samples from the population of all litters that could be used for the study.