The University of Massachusetts Amherst

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What's In A Spreadsheet?

Grad student Thomas Herndon exposes data flaws in a seminal theory of economics
  • Thomas Herndon with Stephen Colbert

Herndon demonstrated in advanced economies average Gross Domestic Product (GDP) growth does not dramatically change when ratios of public debt to GDP rise above 90 percent. 

UMass Amherst economics graduate student Thomas Herndon ’16 (above left) has become an international celebrity, though he never set out to be one. For one of his classes Herndon was asked to replicate the results of a study. He chose the seminal 2010 study by renowned Harvard economists Carmen Reinhart and Kenneth Rogoff that analyzed the relationship between post–World War II public debt and gross domestic product (GDP) growth in advanced economies. The study, widely cited as the basis for austerity policies in Europe and the U.S., argued that economic growth consistently tumbled once government debt exceeded 90 percent of a country’s GDP.

As he began working on the project, Herndon was unable to successfully replicate the results of the original study. Herndon contacted Reinhart and Rogoff, who sent him their original data. As Herndon reviewed the spreadsheet, he quickly found that a series of data errors and insupportable statistical techniques had altered the relationship between public-debt levels and GDP growth. In fact, Herndon demonstrated, in advanced economies average GDP growth does not dramatically change when ratios of public debt to GDP rise above 90 percent.

Herndon went on to collaborate with two UMass Amherst professors of economics, Michael Ash and Robert Pollin, on a report titled “Does High Public Debt Consistently Stifle Economic Growth? A Critique of Reinhart and Rogoff.” Published April 15, 2013, it immediately gained international attention and sparked pointed criticism of politicians and policymakers who had made the Reinhart and Rogoff study the basis of their debt-cutting fiscal plans.

Within two weeks Herndon was profiled by the New York Times, Wall Street Journal, and Washington Post, got coverage from numerous European and Canadian media outlets, and was interviewed or featured on the Bloomberg Network’s Street Smart, MSNBC’s Last Word With Lawrence O’Donnell, and Comedy Central’s Colbert Report. Stephen Colbert asked Herndon what many people might wonder, given the array of powerful people his findings have discomfited: “Do you have someone starting your car for you right now?”


Emery Berger Wins Microsoft Award for Tool That Finds Spreadsheet Errors

Emery Berger (computer science) received a 2013 Microsoft Research Software Engineering Innovation Foundation (SEIF) Award, which includes $25,000 grant, for his work on a system to automatically find errors in spreadsheets. 

Berger's CheckCell program, one of only 16 projects selected worldwide for SEIF Awards, makes it possible for users of Microsoft Excel to find mistakes in spreadsheet data. 

Emery BergerBecause spreadsheets are widely used in businesses, Berger says, the impact of errors can be dramatic. "Errors in spreadsheet data have led to losses of millions of dollars," says Berger. "CheckCell can automatically find mistakes like typos or other data-entry errors."

The CheckCell system that Berger and his graduate students have devised works by examining the interaction of the data in each cell in a spreadsheet with other parts of a spreadsheet such as formulas or charts. When CheckCell finds cells that have an unusually high impact on a formula or a chart, such as making a pie wedge change dramatically in size, CheckCell marks the responsible cells in red. "The darker the red is, the 'weirder' the value is," says Berger. "That means that either the value is extraordinarily important or, more likely, that it actually is a mistake."

Berger hopes that the technology in CheckCell will eventually become a part of standard spreadsheets. "When you make a spelling or grammatical error in a word processor, you immediately get a squiggle underneath the mistake. That makes it easy to find and fix. We view CheckCell as a kind of spell-checker for spreadsheets that will help users avoid costly mistakes." 

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