A FEW years ago Hans Rosling, the celebrated doctor, public educator and professor of international health, was invited to make a presentation at Edinburgh’s Balmoral Hotel.

His audience of capital managers and their wealthiest clients listened as he told them that the best countries to invest in were those African nations, including Nigeria, that had made rapid improvements in education and child survival.

At the end, Prof Rosling was packing away his laptop when a “grey-haired man in a lightly checked three-piece suit” came up to him and quietly assured him that Africa didn’t have a snowball’s chance of making it – and he knew, because he’d worked in Nigeria. The man disappeared before Rosling could think of a fact-based reply.

The man’s blinkered, "I know best", attitude was a perfect example of what Prof Rosling spent much of his life trying to counter.

Prof Rosling died in February 2017, aged 68, but his pioneering work – to, in the words of Bill Gates, offer “clear, actionable advice for how to overcome our innate biases and see the world more factfully” – has continued.

His final book, newly published and co-written with his son and daughter-in-law, Ola and Anna, has been praised by Gates as “one of the most important” he has read. The book is entitled Factfulness: Ten Reasons We’re Wrong About the World – And Why Things Are Better Than You Think. Factfulness is described as “the stress-reducing habit of only carrying opinions for which you have strong supporting facts.”

Gates himself declared last month: "Hans believed the world was making remarkable progress, and he wanted everyone to know about it. Factfulness is his final effort to help people identify areas where things are getting better and spread that improvement. It explains more clearly than almost anything else I’ve read why it’s so difficult for people to perceive progress."

Prof Rosling, who was born in Uppsala, Sweden and trained as a doctor, worked in Nacala, Mozambique, as a district medical officer between 1979 and 1981. From 1997 onwards he was professor of international health at Stockholm’s Karolinska Institute. In 2005 he, his son and his daughter-in-law established the Gapminder Foundation, aiming to counter “devastating ignorance with a fact-based worldview.”

He became famous for his lively and informative TED talks, which ranged across such subjects as the rise of Asia, and new insights into poverty. Together they have been viewed more than 35 million times and translated into many languages. The second talk even saw him demonstrate his sword-swallowing party trick.

He became known as a “data rock star”, capable of getting us to challenge our preconceived ideas about the world. He always argued that the world was in much better shape than we gave it credit for.

To make a point, Prof Rosling once conducted a test involving chimpanzees answering questions at random about the state of the world and discovered that they consistently outranked investment bankers and Nobel laureates. A chimp randomly selecting an answer was more likely to haphazardly hit on the truth than a seemingly bright, but innately biased, human being.

One of his key questions to his human audiences over the years concerned the proportion of the global population that lived in extreme poverty. Only seven per cent of his audiences ever gave the correct response - namely, that the proportion has halved over the last 20 years. “This is absolutely revolutionary,” he writes of the statistic in the book. “I consider it to be the most important change that has happened in the world in my lifetime. It is also a pretty basic fact to know about life on Earth. But people do not know it."

In 2012 TIME magazine made him one of the world's 100 most influential people, saying that his greatest impact "has come from his stunning renderings of the numbers that characterize the human condition".

Factfulness brings together the ten instincts that make us wrong about the world, including negativity, fear, generalization, single-perspective, blame and destiny. The Edinburgh man who was utterly convinced that Africa would forever remain a basket-case was obeying the destiny instinct - the idea, says Prof Rosling, "that innate characteristics determine the destinies of people, countries, religions, or cultures. It's the idea that things are as they are for ineluctable, inescapable reasons."

There was one other instinct he singled out - the gap instinct: "The irresistible temptation we have to divide all kinds of things into two distinct and often conflicting groups, with an imagined gap - a huge chasm of injustice - in between."

In the book's closing pages Prof Rosling, who was diagnosed with incurable pancreatic cancer in February 2016, says that combating ignorance and spreading a fact-based worldview had been an occasionally frustrating but ultimately inspiring and joyful way to spend his life.

"I have found it useful and meaningful to learn about the world as it really is. I have found it deeply rewarding to try to spread that knowledge to other people." It was definitely possible that everyone would one day have a fact-based worldview, he wrote - it is more useful for navigating life, and it creates less stress and hopelessness "than the dramatic worldview, simply because the dramatic one is so negative and terrifying".

"When we have a fact-based worldview," he added, "we can see that the world is not as bad as it seems - and we can see what we have to do to keep making it better."