As American equity investors and their advisers will tell you, it is “stocks for the long run,” report the latest edition of The Economist. Over time, equities perform better than bonds. Even had you put all your money in shares just before the stockmarket crashes of 1929 or 1973, you would in the end be far richer than the wallflowers who played it safe with bonds. That was the thrust of a best-selling book by a business-school professor at Wharton, Jeremy Siegel, first published in 1994. By the end of the decade, it was common wisdom that every dip in share prices was merely an opportunity to buy.

Others have taken the notion to wacky extremes. In 1999, another popular book, Dow 36,000, predicted that the Dow Jones industrial average would nearly quadruple in three or four years (it is now around 9,800, and thus about where it was three years ago). Though the book’s author has since revised his target date to maybe “the end of this decade”, he remains unrepentant about his core thesis: whether shares are cheap or dear at current prices, they are the safest way to guarantee long-term wealth. Books by others bid the target up still higher: Dow 40,000, for one, and Dow 100,000, a $25 volume now discounted at $7.50.

Some of America’s affection for sharesÑmore American households have their savings in equities than in any other countryÑis understandable. In stockmarkets, the victors write the history, and most academic analysis of equity performance has been based on stockmarkets in America, which happened to be the most successful large economy of the past century. Moreover, nearly all analysis has focused on the years after 1925, for which the best data is available. Far less attention has been lavished on other parts of the world, or on earlier periods in America.

Sponsored by ABN Amro, a new study by two professors and a research director at the London Business School, Elroy Dimson, Paul Marsh and Michael Staunton, takes a more cosmopolitan view. Their book escapes the tyranny of American data; it looks at indices of total returns for 16 rich countries, using newly gathered data going back to 1900, a full quarter-century earlier than most other studies.

Have they put paid to the notion that shares beat bonds? No: actually, they confirm it, hence the book’s title: Triumph of the Optimists. In every country in their study, the authors show that real (that is, inflation-adjusted) returns from equities beat bonds. Still, the devil, like the risk, is in the details.

The equity premium (also known as the equity-risk premium) is a measure of the average annual return over and above riskless debt, such as government bonds, that shareholders expect to receive as compensation for holding risky shares. This risk is no illusion: shareholders are always the last to be paid, after other creditors get their cut. The authors conclude that all the world’s stockmarkets offer strong evidence that riskier assets, on average, return more to investors.