In this excellent article on data and gender, Melinda Gates points out that many women disappear from statistics and from the records of governments and quangos, simply because their existence is never recorded.

Presumably the 200 Chibok girls who were abducted by Boko Haram could have been rescued more easily if they had been better documented - to date, only one of them has been rescued.

It would be easier to prevent female genital mutilation, forced marriages, child marriages, and other horrors, if the data on women existed.

The Bill and Melinda Gates Foundation is going to invest $80 million over the next three years to help improve the way data is collected   and used.

This will provide a much more detailed picture of the challenges women and girls face, and what can be done to overcome them.