My understanding of the results: for the preregistered tasks you measured effects of 1 IQ point (for RAPM) and 2.5 IQ points (for BDS), with a standard error of ~2 IQ points. This gives weak evidence in favor of a small effect, and strong evidence against a large effect.
You weren’t able to measure a difference between vegetarians and omnivores. For the exploratory cognitive tasks you found no effect. (I don’t know if you’d expect those tests to be sensitive enough to notice such a small effect.)
At this point it seems a bit unlikely to me that there is a clinically significant effect, maybe I’d bet at 4:1 against the effect being >0.05 SD. That said I still think it would be worthwhile for someone to do a larger study that could detect a 0.1 SD effect, since that would be clinically significant and is very weakly suggested by this data (and would make supplementation worthwhile given how cheap it is).
It seems quite likely to me that all the results on creatine and cognition are bogus, maybe I’d bet at 4:1 against there being a real effect >0.05 SD.
Unless I’m misunderstanding, does this mean you’d bet that the effects are even smaller than what this study found on its preregistered tasks? If so, do you mind sharing why?
Yes, I’d bet the effects are even smaller than what this study found. This study gives a small amount of evidence of an effect > 0.05 SD. But without a clear mechanism I think an effect of < 0.05 SD is significantly more likely. One of the main reasons we were expecting an effect here was a prior literature that is now looking pretty bad.
That said, this was definitely some evidence for a positive effect, and the prior literature is still some evidence for a positive effect even if it’s not looking good. And the upside is pretty large here since creatine supplementation is cheap. So I think this is good enough grounds for me to be willing to fund a larger study.
My understanding of the results: for the preregistered tasks you measured effects of 1 IQ point (for RAPM) and 2.5 IQ points (for BDS), with a standard error of ~2 IQ points. This gives weak evidence in favor of a small effect, and strong evidence against a large effect.
You weren’t able to measure a difference between vegetarians and omnivores. For the exploratory cognitive tasks you found no effect. (I don’t know if you’d expect those tests to be sensitive enough to notice such a small effect.)
At this point it seems a bit unlikely to me that there is a clinically significant effect, maybe I’d bet at 4:1 against the effect being >0.05 SD. That said I still think it would be worthwhile for someone to do a larger study that could detect a 0.1 SD effect, since that would be clinically significant and is very weakly suggested by this data (and would make supplementation worthwhile given how cheap it is).
(See also gwern’s meta-analysis.)
Unless I’m misunderstanding, does this mean you’d bet that the effects are even smaller than what this study found on its preregistered tasks? If so, do you mind sharing why?
Yes, I’d bet the effects are even smaller than what this study found. This study gives a small amount of evidence of an effect > 0.05 SD. But without a clear mechanism I think an effect of < 0.05 SD is significantly more likely. One of the main reasons we were expecting an effect here was a prior literature that is now looking pretty bad.
That said, this was definitely some evidence for a positive effect, and the prior literature is still some evidence for a positive effect even if it’s not looking good. And the upside is pretty large here since creatine supplementation is cheap. So I think this is good enough grounds for me to be willing to fund a larger study.