How Large a Sample Do You Need?

And is sample size even the right question? I regularly conduct both qualitative and quantitative research. Regardless of qual or quant I'm often asked about sample size. An economist might balk at the idea that you can get value from 5–10 1 hour interviews. Yet there is a lot of value in qualitative research that can't be achieved with quant. And quantitative research has its own perils -- including sample size issues. Questions about sample size are more complex than they appear. A proper answer requires nuance. It depends on the theoretical justification for the results, the effect size observed, the number of hypothesis, and more.