Ratings, historically, have given the public a sense of how popular a show is... and for advertisers, to know if their dollars are being well spent (and how much they would expect to pay up).The thing about ratings is that we are in an era where they are taking on less and less relevance. Due to streaming, on-demand, and DVRs very few people actually watch their shows on broadcast night anymore. Indeed, AMC actually offers new Walking Dead episodes on their streaming service 48 hours before they air, which is likely a factor in why the Sunday night numbers tend to be so low here lately. Granted, there are still too many decisions being made in the TV industry based on broadcast night ratings, but I get the impression that AMC at least is taking a broader look at the bigger picture and realizing Walking Dead is still a very popular show, more so than the Sunday night numbers would indicate anyway.
Certainly with On Demand, and cable boxes, there are new, more accurate ways to measure viewer interest...and unfortunately, those numbers are often NOT made public (other than perhaps subscriptions, but fo rthe SERVICE AS A WHOLE, and usually NOT for a particular series).
It would be nice to know how much viewership has REALLY gone down over the years, and if there are any overlap audiences with other shows, or repeat viewings.