This is the annual Roy Morgan "survey" of AFL supporters and membership.
http://www.roymorgan.com/findings/8088-afl-supporter-ladder-june-2019-201908160718
It still has its basic problem in that it is a survey, e.g If you survey people in NSW about their favourite team they will nominate the Sydney Swans. So to extrapolate that to Australia-wide support of 1.1M supporters is simply ludicrous. That their "supporter" numbers could drop by 6% in one year should tell them their methodology is wrong......however...
the best part of the article is the profile of the typical Melbourne Demons supporter:
"In 2019 the quintessential supporter of the oldest football club in the land is well-educated, Victorian, and with a diploma or degree under his belt. Yes, he’s more likely to be male than female. He’s a young parent under 35 years old with pre-school aged children and likely following in the footsteps of his Melbourne supporting parents ".....etc
Anyhow.....enjoy the read.....