In development, there are lots of statistics. Every once in a while, a number jumps out at you because it expresses a complicated truth in simple terms. Here's one that jumped out at me: 20 per cent. That's how much more likely it is that a child will survive when the family's budget is controlled by the mother.
Women know what's best for their families. They invest in health care, nutritious food and education. The tragedy is not just that most women don't control household budgets; it's that many don't control the circumstances of their own lives. If women everywhere had the power to determine their futures, the world would be forever transformed.
That's why I'm proud to attend the Women Deliver conference this week in Kuala Lumpur, along with more than 3,000 people who have dedicated their careers to empowering women and girls.
One key to empowerment is letting women decide when to have children. Right now, more than 200 million say they don't want to have a child but are not using contraceptives. Some will die from complications of pregnancy. Some will give birth to a child who dies. Many mothers who survive won't have the resources to feed or educate the children.
Take, for example, a girl in Niger, where 75 per cent of girls are married before their 18th birthday. Niger is small and has the world's highest rate of child marriage, but there are large countries, like India and Bangladesh, where more than 40 per cent of girls become brides.
What happens to a child bride from one of these countries? If she can't use contraceptives, she gets pregnant, leaves school, and probably never goes back. If she continues having children one after the next, her health will deteriorate, along with the health of her babies. By the time her children are of school age, they are likely to be malnourished and stunted.
However, if these girls don't get pregnant and are able to stay in school, everything changes. They will be healthier. Their children will be healthier. Because they finished their schooling, they will be able to earn more. That money will stretch further, because they will be supporting a smaller family. Their children will be set up to lead a better life than they did, which is the goal of every parent I know.
Last year at the London Summit on Family Planning, the world came together on a goal to reach 120 million more women and girls around the world. Since the summit, almost two dozen countries have developed plans to make sure women have access to contraceptives.
Family planning is just the start. Women must also have the power to vaccinate their children, feed them healthy food, and pay their school fees. Each of these is a link on a chain of good health and prosperity.
Take agriculture. The vast majority of the world's poorest people farm small plots of land to grow their food and earn an income. Women do the majority of the agricultural work across Africa and South Asia, but they don't have equal access to information and farm supplies. As a result, plots of land worked by women generate lower yields than plots worked by men. If women can get the right training, high-quality seeds, and access to irrigation and fertiliser, they will be able to grow more and more nutritious food while producing a surplus they can sell for a profit.
Women Deliver is organised around the conviction that women and girls can start a virtuous cycle of development. They just need a little support to get it started. Once the basics are in place, the only limit is women's ambition for the future.
Melinda Gates is co-chair of the Bill & Melinda Gates Foundation