'Sexist' data is holding women back, Bill and Melinda Gates say

"Sexist" data is making it harder to improve women and girls' lives, the world's leading philanthropic couple Bill and Melinda Gates have said in an open letter.

The couple warned that a lack of focus by researchers on gender and a disdain for what were perceived as "women's issues" were resulting in "missing data" that could lead to better decisions and policies, enable advocacy and measure progress.

"The data we do have - data that policymakers depend on - is bad. You might even call it sexist," Melinda Gates wrote in their annual letter discussing the work of their foundation, one of the largest private charities in the world.

Gender inequality is one of the greatest barriers to human progress, the United Nations said last year, with studies showing that when girls stay in education, they have more opportunities and healthier children, which boosts development.

But data often does not take gender into account and is flawed by biased questions, said the husband and wife team behind the Bill & Melinda Gates Foundation.

Because women in developing countries are primarily seen as wives and mothers, most of the data about them focuses on their reproductive health, not their earnings and assets, they said.

"You can't improve things if you don't know what's going on with half the population," wrote Gates, co-founder of Microsoft Corp.

The couple said mobile phones offered a powerful tool to allow women to build new connections, gain economic freedom and challenge restrictive social norms, for example by buying contraceptives online.

"If you're a woman who has never stepped into a bank, mobile banking offers you a foothold in the formal economy and a chance at financial independence," said Melinda Gates.

"You gain opportunities to connect with customers, trainings, and professional organisations - all from your home."

Toilets also emerged as a feminist issue, with the couple hailing a next generation of facilities which can kill pathogens and produce useable by-products such as fertiliser.

Safe toilets worldwide would especially benefit women and girls, they said, who risk assault while using public facilities or may be forced to skip school when on their periods.

International aid groups agreed more of a focus on women and girls was needed.

"We can't improve what we fail to measure," Richard Morgan, international advocacy director at the child rights charity Plan International, told the Thomson Reuters Foundation.

"Bringing visibility to girls and women is the first critical step in improving their lives."