Thanks for the feedback.

I think it's debatable actually - while intersecting the list with another does give you less bias, it also reduces the sample size immensely (as happened in the 2011 analysis I linked to), so there are trade offs in both directions.

I'm not claiming that I know exactly how many accounts reuse passwords - I am suggesting that, based on my estimate, it is more than half.

The evidence (that I've linked to) supports this. There are other studies which show upto 60% of password reuse: http://www.troyhunt.com/2012/07/what-do-sony-and-yahoo-have-...

If you can produce a better estimate please go ahead.