7 points for yellow? Really?

This is a statistic that is thrown out there all the time and it has for years. I've always been sceptical as for most yellow cards I've seen a team often only concedes a penalty or two and often end up in the +. So does it come from? Is it just based on a converted try? Is from genuine analysis and has kept running?

I'm pretty sure the BBC had some 6 nation analysis that showed that Wales on average let in about 7 points but they were the worst and most of the others were around 2 and I think England may have been +.

Here's some analysis but it's not complete - http://www.bestrugby.eu.org/?p=1680

So 4.8 points overall for a yellow card. Although there is a large range depending on the team (in the 6 nations anyway).

But more often that not it changes the flow , tempo, swing of a game. Even if it doesn't result in points it does often prevent the other team from scoring (or at least as much) and that can matter. Also psychologically the offending team will find it harder to lift themselves unless it was a particularly controversial yellow even after the player returns. And also the player with a yellow will probably be a little tackle shy after too.

Plus the way Alain Rolland gives them out it'll just be normal course of play

It used to be 10points were the norm for a Yellowcard,some teams have actually not conceded points but scored them.[The AllBlacks] 2010.