This year, I concentrate on the power of clear goals and accurate measurement–simple concepts really–to improve the lives of the poorest people around the globe. It may not be the sexiest of themes, but the proof of its impact is undeniable. The lives of the poorest have improved more rapidly in the last 15 years than ever before. During that time, the number of people living in extreme poverty has been reduced by half–extraordinary progress in a short period of time. Read the 2013 letter.