Are You a Terrible Investor? If You Do This, You May Be

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It's beginning to look like much of the world fell in love with austerity economics under false pretenses. 

One of the cornerstones of the recent love affair with austerity was a paper by economists Carmen Reinhart and Kenneth Rogoff that argued that when debt-to-GDP ratios breach 90%, economic growth takes a dive. But now it looks like an Excel coding error -- among other things -- may have led to the wrong conclusion

This hardly the only time that Excel has been at the center of some boneheaded financial mishaps. In the run-up to the financial crisis, spreadsheet models that predicted blue skies and no housing downturn (ever!) ran rampant. More recently, as Paul Krugman reminded readers, an Excel error played a part in JPMorgan Chase's (NYSE: JPM  ) London Whale debacle:

After subtracting the old rate from the new rate, the spreadsheet divided by their sum instead of their average, as the modeler had intended. This error likely had the effect of muting volatility by a factor of two and of lowering the VaR...

In a similar vein, last week, I showed how evaluating the same data in slightly different ways can lead to very different conclusions.

This is not, of course, Excel's fault. That'd be like blaming a shovel after someone dug a hole in the wrong spot. Instead, they're all great illustrations of what can happen when we start to rely on data, models, and calculations and stop thinking about those data, models, and calculations.

Austerity economics may not be a day-to-day concern for many readers. And few of us are managing multi-billion dollar portfolios, as JPMorgan's CIO office is. But as investors, our lexicon includes back-of-the-envelope valuation metrics like the price-to-earnings ratio. Company efficiency evaluations include returns on equity. And in some cases, we may be building Excel models of our own to try to triangulate the value of a stock.

This can all be useful. There are literally thousands of publicly traded stocks in the U.S. alone, and the ability to use quick-and-dirty metrics to choose companies to dig into further can make an impossible task -- deep dives on several thousand companies -- into a more manageable one. 

But it's tempting to rely too much on the results of these calculations. Reinhart and Rogoff's paper was not peer reviewed, and the Excel spreadsheet was not shared (until recently). It was a black box that policy-makers around the world were leaning on just like the mortgage-backed securities traders of 2007.

In a similar way, we can say that Bank of America  (NYSE: BAC  ) trades at a tangible book-value multiple of 0.86 and has a return on assets of 0.3%. Each at their face seem to tell a particular story. But it's a mistake to conclude that that story is the reality of B of A without further exploring what's on the bank's balance sheet, how much legal settlements can still sap its accounts, and to what extent one-time events and accounting oddities are impacting its current results.

I've long been a fan of Excel modeling in my own investing. For me, though, the act of building and tweaking a financial model is always an exercise in illuminating and better understanding the details that lie behind the conclusion -- not obscuring them.

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Read/Post Comments (4) | Recommend This Article (8)

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Help us keep this a respectfully Foolish area! This is a place for our readers to discuss, debate, and learn more about the Foolish investing topic you read about above. Help us keep it clean and safe. If you believe a comment is abusive or otherwise violates our Fool's Rules, please report it via the Report this Comment Report this Comment icon found on every comment.

  • Report this Comment On April 18, 2013, at 10:35 PM, southwestrancher wrote:

    So what exactly are you saying? Is it a good investment or not? At tangible book-value multiple of 0.86 and big earnings growth coming out of recession it can't have had that great an impact nor will it. Strong Buy

  • Report this Comment On April 19, 2013, at 11:16 AM, Weaselbait wrote:

    This article is _not_ about BAC, it is about making public announcements about one’s conclusions on the subject of macroeconomic trends without making one’s data and methodology available for peer review.

    BAC is merely mentioned as an object lesson - - that financial accounting ratios should be a starting point in one’s analysis - - not a buy or sell signal; without studying the import of the underlying numbers. Likewise, one should be skeptical about macroeconomic assertions without the chance to analyze the methodology (…”I used EXCEL…” doesn’t cut it).

    BAC is probably the most hated name on Wall Street (undeservedly so in my opinion) and, as such, is subject to hyperbole in both directions when it comes to speculation as to what price its stock deserves. Much of the hyperbole would disappear if people really understood what the numbers meant instead of shooting off their mouths with worthless speculation and innuendo. Ninety-five percent of what purports to be “news” about BAC is demonstratively wrong and misleading.

  • Report this Comment On April 19, 2013, at 6:31 PM, Reinoutjr wrote:

    You may be a terrible investor if you do: what..?

  • Report this Comment On April 19, 2013, at 6:46 PM, nerd51 wrote:

    "Austerity economics may not be a day-to-day concern for many readers." Really? It should be. Whether you agree with austerity as an economic policy to promote growth or not, these policies have a profound impact on all of us. Take your eyes off of Wall Street long enough to see how Washington is affecting Main Street.

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