With proper random sampling you only need something like N = 27 (I forget exactly) to reach p = 0.05
Assuming random sampling, it's a misconception that you need ten thousand participants to have a useful study.
Assuming random sampling, it's a misconception that you need ten thousand participants to have a useful study.
It feels like everything to say has already been said about the bias of small sample sizes and the dangers of p-hacking. But it also seems like the discussion is inevitable here.
I wonder if there’s a new insight to glean, somehow...
For a background on why p-values are misleading, see https://youtu.be/42QuXLucH3Q which is excellent. He points out that 0.05 was selected by Ronald Fischer in 1925, and people have gone with it since.
Root parent comment is right to question if the N=266 is truly random given the description we do have at hand.
You are right to say N=266 could be truly random and we don't have enough information to definitively decide either way.
We can't read the study so it's just what we have - saying you have a truly random sample with a group just from Barcelona is extremely hard to accept. I mean even you've got to admit that.
will be difficult to demonstrate that they can control for all individual differences at n=266 to prove differences in dementia outcomes are linked to a single variable.
Of course actually picking 27 random people is extremely hard, so actual studies compensate by picking more people.
It's highly dependent on the magnitude of the effect (when comparing two populations) and the distribution across a population.
For something dementia, where even measuring the level of cognitive decline is highly subjective, no way N=27 would be enough.
That being said, article mentions 63+135+68 individuals in 4 hospitals in a single city.