Yowzers -- just squeaked by on that one, didn't they. Given the unknowns around dropouts, I would be frankly astonished if these results stood up. It mainly looks like the "speed" category dubiously "benefited" from a higher death rate; the ~20 excess deaths in that subset can neatly account for ~2 additional cases that drives significance to random-chance levels again.
In addition, the meta-analysis seems to indicate that only memory-based interventions work, while the individual study linked showed differently. Hopefully as pre-registration becomes mandatory it should become clearer how many of these studies were abandoned because of null results.
I feel like I am of those that can easily be fooled by misleading claims.
From [2] (the crash results), deaths and drop-outs were handled by adjusting crash rates to total person-year exposure times. In this study as a whole, non-completion rates were not significantly different across groups.
Yes, pre-registraton is an excellent idea.
Here's a meta-analysis of 97 published randomized controlled trials, showing reliable improvements in cognitive function and transfer to real-world function [1]
Here's an NIH-funded study of more then 2,800 older adults followed for 10 years showing that speed-of-processing training reduces the risk of dementia by 29% [2]
Disclosure: I work at a cognitive training company.
[1] PDF link: https://www.researchgate.net/profile/Catherine_Mewborn/publi...
[2] https://www.sciencedirect.com/science/article/pii/S235287371...