United Kingdom

79% and 20% are two different stats. The 79% is the percentage of people who at some point, any point, in a week watch live TV. Even just one minute. 20% is the average share of people who are watching at 9pm, so one in five people are watching.

There's a lot of selection bias in your estimate. When I walk the dog I go past lots of houses that have their TVs mounted so they are visible from the street, and there's plenty that are watching live TV. It's not just major events like sports, but many people have it on for soaps, a distraction for the kids, or just mindless guff like The Chase. I'd say it's easily one in five out in suburbia.