Local Forecasts: VSS vs. eMarketer

Today, from eMarketer (all geotargeted online advertising): $7.8 billion by 2011

Here’s Veronis Suhler Stevenson’s (VSS’s) earlier forecast for online Local ad spending: $19.2 billion by 2011

Source: VSS (8/07)

While the categories may be slightly different both forecasts seek to capture the full array of geotargeted advertising online and its projected value by 2011. The VSS forecast is almost triple the eMarketer forecast; however VSS asserts that it has the most accurate forecasting record in the industry:

The VSS Forecast also features the industry’s most accurate spending forecasts, producing a margin of error of +/- 2% for 9 of the last 10 years. The margin of error for the 2006 forecasts was + 0.4%.

Borrell’s numbers are also quite a bit larger than eMarketer, though it’s not tracking as many categories as VSS.

There are similarly divergent numbers for mobile advertising, which in a way is more understandable given how new and generally speculative the medium is at this point. But how can the VSS and eMarketer forecasts be so far apart? Are the assumptions wrong? Are the underlying data incomplete? Is the methodology flawed?

What do you think?