Bill and Melinda Gates are optimistic about the future, and they think you should be, too.

As the co-chairs of the Gates Foundation explain in their recent Gates Letter, an annual review of global progress, the world is doing a lot better than the public gives it credit for.

People aren't as poor, as sick, or as unequal as they used to be.

The letter includes a dizzying number of charts, graphs, and stats illustrating that point, but here are four that highlight some of the Gateses favourite leaps.