Although I have no doubts that iron deficiency is a problem, I do not think the evidence linked for this is particularly strong backing for it having massive effects. In particular, estimating the cognitive impacts of anything from one study that hits marginal statistical significance with a massive estimated effect size (0.5 standard deviations) seems likely to lead to a wildly inaccurate estimate of the true effect. This is because this study possesses all the hallmarks of low statistical power interacting with publication bias.
Furthermore, given that the the other studies appear to have small samples sizes (note: I am an economist, not a medic) and the p-values are not far off 0.05, I would be worried about publication bias exaggerating any effects there as well, especially as I suspect studies conducted fifteen to twenty years ago were unlikely to be pre-registered.
To convince me of an effect size, I would want to see a study with p<<0.01 or a meta-analysis of RCTs that addresses the issue of publication bias.
Although I have no doubts that iron deficiency is a problem, I do not think the evidence linked for this is particularly strong backing for it having massive effects. In particular, estimating the cognitive impacts of anything from one study that hits marginal statistical significance with a massive estimated effect size (0.5 standard deviations) seems likely to lead to a wildly inaccurate estimate of the true effect. This is because this study possesses all the hallmarks of low statistical power interacting with publication bias.
Furthermore, given that the the other studies appear to have small samples sizes (note: I am an economist, not a medic) and the p-values are not far off 0.05, I would be worried about publication bias exaggerating any effects there as well, especially as I suspect studies conducted fifteen to twenty years ago were unlikely to be pre-registered.
To convince me of an effect size, I would want to see a study with p<<0.01 or a meta-analysis of RCTs that addresses the issue of publication bias.
I agree: the available evidence is incredibly low quality. If you find something better I’d be delighted if you shared it.