Alternatives to Animal Use in Research, Testing, and Education (Part 8 of 27)

Investigators often ask statisticians how many observations they should make (fortunately, usually before the study begins). To be answerable, this question needs fuller formulation. There is a resemblance to the question, How much money should I take when I go on vacation? Fuller information is needed there too. How long a vacation? Where? With whom? Three questions need to be answered before the sample size is determined. How variable are the data that will be collected? How precise an answer is needed? How much confidence should there be in the answer obtained? These questions can be well worth probing even if the question of sample size will foreseeably be answered by the size of the budget or the time available for the study. Sometimes a planned study is dropped because sample-size analysis shows that it has almost no chance of providing a useful answer under the constraints of time or budget that apply.