By Noah Smith The Guardian recently reported a startling development\u2014according to the charity Oxfam, a handful of the world\u2019s richest people got much richer in 2018, while half of the world\u2019s population got much poorer. On Twitter, writer Anand Giridharadas summed up the dire implications: When Giridharadas urges us not to \u201cbe Pinkered\u201d into complacency, he is referring to psychologist Steven Pinker, whose books convey the message that life for large numbers of people has been improving. By this point, everyone knows\u2014or ought to know\u2014that inequality has been rising within most developed countries. This has been made clear by a steady drumbeat of statistics, as well as economist Thomas Piketty\u2019s landmark 2014 book, Capital in the Twenty-First Century, which confirmed that inequality has generally increased within rich countries since about the middle of the 20th century. Nor can anyone ignore the glaring disparities between the global ultra-rich, who gathered at Davos, Switzerland, this week to ski and network and praise themselves, and the billions of people in poor countries who still subsist on just a few dollars a day. To anyone who is upset about these disparities, Oxfam\u2019s numbers simply add one more call for alarm. But the charity organisation\u2019s dire reports should be taken with a grain of salt. The truth is that wealth inequality, though substantial, probably isn\u2019t skyrocketing. First of all, Oxfam\u2019s numbers look dubious. If the wealth of half of the world\u2019s people really fell by 11% in one year, as Oxfam says, it would signal the coming of an enormous global recession. But 2018 economic growth numbers look healthy\u2014the International Monetary Fund estimates that almost every economy in the world grew last year, with only a small handful of exceptions. That suggests something funny is going on with Oxfam\u2019s data. One reason might be that wealth is inherently hard to measure, especially in developing nations. In those countries, much wealth tends to be held in the form of real assets, like houses owned by poor farmers, or informal businesses, like a family-run food stand in a big city. There are typically no well-functioning, transparent financial markets for these assets, so it is hard to get a reliable estimate of their value. That is not to say that the global poor have lots of hidden wealth squirrelled away. Instead, what it means is that changes in the estimated value of wealth in developing nations are likely to come from changes in the assumptions of the researchers doing the estimation, or changes in data availability. This can be seen in Oxfam\u2019s numbers. Oxfam gets its wealth data from Credit Suisse, which provides yearly updates to its estimates. Comparing the 2017 wealth estimates to the 2018 updated estimates for 2017, we can get an idea of how much these numbers tend to vary: These differences can\u2019t be coming from actual wealth changes, since both estimates are for 2017; they come from data revisions. Sometimes these data revisions are small, but other times very large\u2014for China, the difference is more than twofold! Even for rich countries, the data revisions can be big\u2014for Japan, the difference was about 18%. If data revisions are regularly this big, then Oxfam\u2019s assertion that wealth inequality went up substantially in 2018 could easily be illusory. In rich countries, meanwhile, wealth depends mostly on asset prices, especially the prices of stocks and real estate. As anyone who lived through the 2008 financial crisis keenly remembers, these prices can be affected by investor sentiment that has little to do with the real underlying value of physical assets\u2014and thus little to do with how much of the world\u2019s actual resources people get to consume. If investors decide to pay higher prices for shares of Amazon.com Inc., Jeff Bezos\u2019 wealth goes way up, but the real value of Amazon\u2019s business might be the same as the previous day. For closely held companies, where many rich people derive their wealth, it is even harder\u2014if one investor overpays for a small piece of Uber Technologies Inc., the whole company\u2019s valuation can go up by billions of dollars, but that really just reflects the excessive optimism of that one investor. This means that big swings in the wealth of the world\u2019s top billionaires don\u2019t usually represent changes in the amount of real, physical resources they command\u2014it doesn\u2019t show that they are \u201cmonopolising progress,\u201d as Giridharadas puts it, to any greater degree than before. Wealth comparisons are always hard to do, but they\u2019re even harder when comparing across countries. Big swings in exchange rates can dramatically change the amount of real foreign resources\u2014Nigerian oil or Australian bauxite\u2014that Jeff Bezos\u2019s billions would be able to buy. Finally, as many other writers have noted, wealth calculations include debt, much of which is held by people in rich countries who actually aren\u2019t that poor. By the official definition, when Donald Trump declared bankruptcy, he was poorer than a debt-free subsistence farmer in Somalia. Thus, reported shifts in the wealth of the world\u2019s so-called poorest people can reflect changes in debt rather than swings in the real-asset holdings of the actually destitute. So, although it is good to be concerned with wealth inequality, reports such as Oxfam\u2019s shouldn\u2019t be cause for alarm. The world is a very unequal place, but 2018 probably didn\u2019t make it much worse in any meaningful sense. The real story of 2018 was a positive one\u2014rapid global growth that raised living standards in poor countries such as Ethiopia, India, Bangladesh and Indonesia. Thanks to that growth, global inequality of income\u2014which can be measured more reliably than wealth\u2014is actually falling. So yes, the vast wealth of the Davos set may be annoying, and countries such as the US and China should tax them more. But ultimately, the fate of the world\u2019s poor will depend much, much more on economic growth than on how much rich countries choose to tax their wealthiest citizens. This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.