Yeah I imagine the average dosage of RF across populations has been increasing enough overtime along with rollout of new technologies that you’d be able to correlate some function of adoption of these technologies to population level effects if there was any real significance.
Hands free being what? Keeping using the speaker and setting the phone on a table? Using Bluetooth ear plugs with the phone in a breast pocket? So much we don't know...
So… radio waves cannot be the cause.