One stat that sticks out is the near non-existance of WMCA. Fourty years ago this was often the top station for the teen audience, it regularly beat WABC untill 1968.
It's diminution over the years illustrates clearly what has happened to AM overall. First, technology (FM) took away it's youth audience, it then switched to talk a much older skewing format, and finally sold-off to a religion racket that turns it into a pay-for-play for Elmer Gantrys and right wing hucksters.
Take a listen to Short Wave and you can see AM's sad future.
Lino