Back in 1800, when Swedes starved to death and British children worked in coal mines, life expectancy was roughly 30 years everywhere in the world. That was what it had been throughout history. Among all babies who were ever born, roughly half died during their childhood. Most of the other half died between the ages of 50 and 70. So the average was

The gap instinct makes us imagine division where there is just a smooth range, difference where there is convergence, and conflict where there is agreement. It is the first instinct on our list because it’s so common and distorts the data so fundamentally. If you look at the news or click on a lobby group’s website this evening, you will probably n

The goal of higher income is not just bigger piles of money. The goal of longer lives is not just extra time. The ultimate goal is to have the freedom to do what we want. Me, I love the circus, and playing computer games with my grandchildren, and zapping through TV channels. Culture and freedom, the goals of development, can be hard to measure, bu

We tend to assume that all items on a list are equally important, but usually just a few of them are more important than all the others put together. Whether it is causes of death or items in a budget, I simply focus first on understanding those that make up 80 percent of the total. Before I spend time on the smaller ones, I ask myself: Where are t

The most important thing you can do to avoid misjudging something’s importance is to avoid lonely numbers. Never, ever leave a number all by itself.

the pen down and said, “Do you know why I’m obsessed with the numbers for the child mortality rate? It’s not only that I care about children. This measure takes the temperature of a whole society. Like a huge thermometer. Because children are very fragile. There are so many things that can kill them.

Critical thinking is always difficult, but it’s almost impossible when we are scared. There’s no room for facts when our minds are occupied by fear.

Often the best thing we can do to make a large number more meaningful is to divide it by a total. In my work, often that total is the total population. When we divide an amount (say, the number of children in Hong Kong) by another amount (say, the number of schools in Hong Kong), we get a rate (children per school in Hong Kong). Amounts are easier

I’m a very serious “possibilist.” That’s something I made up. It means someone who neither hopes without reason, nor fears without reason, someone who constantly resists the overdramatic worldview. As a possibilist, I see all this progress, and it fills me with conviction and hope that further progress is possible. This is not optimistic. It is hav