For me, one of the great pleasures of skepticism is finding out I was wrong about something. Rather than feeling guilty about my error, I feel proud that I have learned something and have a better understanding of reality. When skeptics encounter a questionable claim, they do some fact-checking. But what if they don’t realize a claim is questionable? If they feel sure they know the truth, they probably won’t bother to check the facts.

The late Hans Rosling spent a lifetime tracking down the facts about things no one questioned. He developed a multiple-choice test that he administered to diverse groups around the world. Everywhere he looked, he found that most people were wrong about most of the things on the test. His findings are summarized in the book Factfulness: Ten Reasons We’re Wrong about the World—and Why Things Are Better Than You Think. Bill Gates said it was one of the most important books he’s ever read, and I agree with him that it is an indispensable guide to thinking clearly about the world. In every country, the majority of people believe the world is getting worse. But this book shows that the world is getting better, and optimism is justified; it provides rules of thumb about how to think about what we hear.

One of the lessons is not to rely on averages. We all know that “on average,” boys are better at math than girls. The reality is overlapping bell curves, with some girls equaling boys at every level of ability, so reliance on average performance would be terribly misleading and might result in policies that limited the opportunities for girls.

I knew of large Catholic families, and I always assumed that the Catholic church was contributing to overpopulation by its prohibitions on birth control and abortion. I was surprised to learn that there is no major difference between the birth rates of the major religions. And contraceptive use in Catholic-majority countries is 60 percent, compared to 58 percent in the rest of the world.

I always assumed that China’s one-child policy was responsible for its declining birth rate. In reality, there was a huge drop from six to three babies per woman in the ten years preceding the one-child policy, and the number of babies never dropped below 1.5 during the thirty-six years of the one-child policy. It dropped lower in other countries that did not have a one-child policy; in Hong Kong, it dropped even below one baby per woman.

Rosling says it no longer makes sense to divide the world into “developed” and “undeveloped” countries. There are people in every country who fall into each of four income levels, and everywhere there are people who have risen from lower levels to higher levels. We need to appreciate the spread and the fact that for every person in the lowest income level 1, there is one person in the highest income level 4 and five people in the intermediate levels 2 and 3, where most of their basic needs are met.

Some facts that will surprise most people:

In the past twenty years, the proportion of the world population living in extreme poverty has decreased from 29 percent to 9 percent. (In the United States, 95 percent of people chose the wrong answers “doubled” or “stayed the same.” Even in the two countries with the highest percentage of correct answers, Sweden and Norway, 75 percent of people still guessed wrong! With this level of misconception, how can we hope to develop rational anti-poverty programs?)

Worldwide, life expectancy is now at least seventy, with estimates as high as 72.48.

The majority of people do not live in low-income countries but in middle-income countries.

Even in low-income countries, 60 percent of girls finish primary school.

Think the number of young people is increasing? In 2100, the UN predicts there will be two billion children, the same number as today.

Over the past hundred years, the number of deaths from natural disasters has decreased to less than half.

Eighty percent of one-year-old children around the world have been vaccinated.

Worldwide, thirty-year-old men have spent an average of ten years in school; women of the same age have spent nine years (not much less).

Crime is decreasing.

The average number of births per woman worldwide has decreased from five in 1965 to 2.5 today and is still dropping. In the United States, it’s 1.9; in Iran, it’s 1.6. In general, the higher the income level, the smaller the family size.

In 1972, women in Bangladesh had seven children and life expectancy was fifty-two; today they have two children and a newborn can expect to live to age seventy-three.

In Egypt today, the child mortality rate is lower than it was in France or the United Kingdom in 1960.

Did some of these facts surprise you? James Randi jokes that getting a PhD diploma makes the recipient incapable of saying “I was wrong” or “I don’t know.” There is no shame in either of these admissions. In fact, it is shameful not to admit them. A good skeptic is happy to make these admissions and can feel a sense of accomplishment and joy rather than shame or regret.

I urge you to get a copy of this book. No need to spend money: your local library has it or can obtain a copy through interlibrary loan. I urge you to read it and adopt its ten rules of thumb for thinking more clearly about the world. Stand in front of a mirror and practice saying “I was wrong” ten times; it doesn’t hurt a bit, and it doesn’t make you look stupid. Really!