Daily Archives: August 23, 2016

How Not to Excel at Forecasting

This post originally ran four years ago. But since a critical mistake is still being made, it’s time for a repost.

How Not to Excel at Forecasting?

Simply put, use Microsoft Excel. It’s appalling that a survey by ToolsGroup and the Global Market Development Centre (GDMC) found that even though two-thirds of companies in the consumer goods supply chain consider demand volatility and forecast accuracy a high businesses priority, half still rely on Excel spreadsheets for forecasting.

Relying on Excel for forecasting is like relying on:

  • a Longship to get you across the Atlantic

  • your first guess on Let’s Make a Deal to be the right one

  • a shareholder proxy getting on the ballot at a Fortune 500

  • Florida surviving a hurricane season without any major city suffering damage

  • the price of fuel going down and staying down for an upcoming series of spot buys

  • natural resource supply to be consistent and predictable year-over-year

  • a flip of a fair coin to come up heads seven times in a row

Now, it’s true that:

  • the Vikings did make it across the Atlantic in a Longship, but a single storm could sink it

  • the first door you pick, with one-in-three odds, could be the right one, but the odds are actually twice as good if you switch

  • an activist shareholder can sometimes get a proxy on the ballot if he or she has enough time and money, but as pointed out by John Gillespie and David Zweig in Money for Nothing (How the Failure of Corporate Boards is Ruining American Business and Costing Us Trillions), examples are few and far between

  • even though no storms made landfall in Florida in 2011, this is Not a common occurrence

  • gas prices did consistently drop in the USA between September 2008 and December 2008, but have been otherwise steadily rising for the last five years

  • in some years the rice, sugar, and corn crops are almost the same as in the previous year, but given the increase in hurricanes, tsunamis, droughts, and other natural disasters in recent years, this is not a common occurrence

  • yes, heads can come up seven times in a row when flipping a fair coin, but the chances of this happening are less than 1%

In other words, you can forecast with Microsoft Excel, but your chances of doing well, especially given that 90% of spreadsheets have non-trivial errors (and collectively cost enterprises billions, as Fidelity and Fannie Mae found out), are (vanishingly) small (as the complexity of the forecast increases). One has to remember that there’s no intelligence behind a spreadsheet and they are just a source of peril that can cost your organization millions without anyone noticing.