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.
But in the field of global health and development vast blind spots still remain. This is especially true when it comes to even the most basic information on women and girls — where and when they are born, how many hours they work, if and what they get paid, whether they’ve experienced violence, how they die. The hard reality is that in too many areas, data doesn’t exist. What’s more — even where it does exist, it’s often sexist. It misses women and girls entirely, or undercounts and undervalues their economic and social contributions to their families, communities, and countries.