Broadcasters and operators naturally want to grow audiences but failing that they at least want to be able to predict what they will be. Now there is accumulating data suggesting they can do both of these, by measuring the emotional engagement of their audiences. It is more accurate to talk about engagement or immersion rather than raw emotion, because most of the time viewers are not cursing their team’s inept performance or having sleepless nights over a late horror movie. However, many people will find their mood has changed subtly through what they have watched and that has been well known to TV advertisers for years or even decades. The difference now is that social media coupled with online services…