The article was written in 2007 and it says: "Recent research using DNA analysis answered this question about two years ago. Today’s human population is descended from twice as many women as men." So the research, if it exists, was done in 2005, plus or minus one year.
There's an idea I've seen a number of times that 80% of women have had descendants, but only 40% of men. A little research tracked it back to this, but the speech doesn't have a cite and I haven't found a source.
The reproduction rates for men and women (possibly for the whole history of the species) seems like the sort of thing which could be found out, but I'd like more solid information.