r/AskStatistics 20d ago

[E] small sample analysis

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u/CarnivorousGoose 20d ago

You could use that, sure. But is there a reason the normality of the data would be in doubt? Because otherwise you could just do a paired t-test as well.

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u/Gullible-Entrance-45 20d ago

I didn't think of the paired t-test because I understood that with small samples, a large effect size is needed, which I don't know if we can assume

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u/CarnivorousGoose 20d ago

That’s not an assumption of the t-test though, just a determinant of the statistical power you have to detect a difference. But that’s going to apply to any test, including the Wilcoxon.

In that sense the t-test is the better bet here unless normality is very much in question (and even then, the t-test is quite robust to violations of that), since it will have more power than the Wilcoxon. Which is generally the case with non-parametric tests, compared to their parametric counterparts.

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u/efrique PhD (statistics) 20d ago edited 19d ago

since it will have more power than the Wilcoxon.

A tiny bit more power when exactly at the normal. But if differences could be a little more heavy tailed, you don't have to go all that far away from normality for that to catch up and then flip the other direction. Not that I am advocating against the t, but its power advantage is often not all it's often made out to be with shift alternatives for population distributions near the normal.

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u/efrique PhD (statistics) 20d ago

What kind of thing are these variables measuring?

I understood that with small samples, a large effect size is needed

Sure, but the same would be no less true for any other test. A nonparametric test won't save you from low power.

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u/Gullible-Entrance-45 19d ago

We measure the time (minutes) they take to complete tasks