I got a lot of pushback from readers regarding my post yesterday supporting Netflix’s switch from a 5-star rating system to a simple thumbs up/down system. The gist of the complaints is that some people do carefully consider their star ratings, and do value the granularity of being able to say that you like/dislike something a little or a lot. But of course some people take that care. The problem is that most people don’t, and collectively, 5-star rating systems are garbage. This post from YouTube back in 2009 shows it with data: when they had a 5-star rating system, the overwhelmingly most common rating was 5-stars. The next most common was the lowest, 1-star. 2-, 3-, and 4-star ratings were effectively never used. For a personally curated collection, 5-star ratings can be meaningful. But for a recommendation service that averages ratings among all users, they are not. It’s the between designing for the ideal case of how people should behave versus designing for the practical case of how people actually behave.