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A Mean Error

Due to a clerk's typing error, Dennis/Daelyn Charnetzky's home was revalued at $400,000,000 in October 2004. Its previous value was $121,900.

The error has been corrected, but with negative financial impact...not on the Charnetskys but on their city of Valparasio, Indiana. That is, due to the financial error/typo and its lack of early detection, the city used the $400 million dollar valuation as part of its calculation of average property values and corresponding tax rates for the year 2005. The result: The city initiated programs that required a $8 million tax base that was not there because the average value was so inflated by the single large value.

This is exactly the type of error mathematics teachers look for, in order to share the real-life story with their students! First, care is needed in making calculations, even if using technology. Second, the average of a data set is influenced by an outlier that is excessively large or small relative to the other values.

Source: G. Ruethling's "A One-House, $400 Million Bubble Goes Pop," New York Times, February 15, 2006