[meowface]

One standard deviation is fairly significant, though.

I think a lot of people would do mind training once per day for a possible 3-4 IQ increase, honestly. I would.

It's also possible that it only results in a fairly small general IQ increase, but a larger increase in some specific facet of recall or cognition.

[simonster]

It's also possible that it results in an IQ increase only for a specific subpopulation that you may or may not be a part of, e.g. the linked metanalysis says that "international studies tend to find more transfer than U.S. studies" and it does not seem as though the effect for the U.S. studies was significantly different from zero.