That's the issue - we don't actually know what they did. Which means their claims would have to be taken on faith.
Now, maybe other researchers designed different more rigorous studies that are replicable and which show the same effect. That could be the case. The point I'm making here is that the DK paper isn't by itself capable of proving the effect it claims, and that you don't need a statistical argument to show that. Sanity checking the study design is a good enough basis on which to criticize it.
Now, maybe other researchers designed different more rigorous studies that are replicable and which show the same effect. That could be the case. The point I'm making here is that the DK paper isn't by itself capable of proving the effect it claims, and that you don't need a statistical argument to show that. Sanity checking the study design is a good enough basis on which to criticize it.