Medical research is expensive to conduct, so it's not uncommon to see N<20. Additionally, more data is not necessarily better data since humans lie and it's un

Medical research is expensive to conduct, so it's not uncommon to see N<20. Additionally, more data is not necessarily better data since humans lie and it's unethical to force their compliance, so there's more of a risk for bad data with large trials. And throwing out bad data is selection bias.