> Meaning that the effect must be fairly strong to be observable in two studies with n=50?
Do what now? Isn't the problem that it could have randomly happened (especially if people did a bunch of other similar studies that didn't observe an effect, and only these two were published)?
For a publishable effect at smaller n, the effect size needs to be fairly large. If you have a huge number of people in a trial, you can get statistical significance of negligible consequence.
The problem with a single study of n=50 isn't the 50, it's that it's a single study.
That's not quite right. If the study is underpowered at n = 50 --- which is extremely likely --- statistically significant estimates are likely to be inflated. And as power declines, they also become more likely to have the wrong sign (e.g., the study will yield a positive estimate even though the true effect is negative).
