Firstly, most people do NOT keep dream journals. Most people on this forum, maybe. But not the general public.
Secondly, keeping a journal usually improves recall, but that's it. Very few of us, if any, can remember every dream we've had, every night, our whole lives.
I stand by my view that this is not math or science in any way.
If that's true then that's definitely an interesting test. If you find a link to it or something then I'd love to see it.