I would not call study worthless, but to establish causation one could do an experiment where elderly adults are given (1) an opportunity for a free hearing tes

I would not call study worthless, but to establish causation one could do an experiment where elderly adults are given (1) an opportunity for a free hearing test and hearing aids if needed (2) the equivalent amount of cash. Then follow up the two groups to see if group 1 is less likely to develop dementia. My guess is that the results will not be strong.