Because input-output modeling is costly to perform, particularly for a particular situation, it is common to extrapolate available data to a particular situation. For example, the . Federal Highway Administration assumes that, on average, a $1 billion of Federal highway expenditure supported 30,000 jobs in 2007 (FHWA 2008). This number has been widely applied, although recent analysis by Heintz, Pollin and Garrett‐Peltier (2009) suggests that actual impacts are somewhat lower. In addition, the models include many assumptions that may be inaccurate or outdated. For example, the IMPLAN Input-Output Model apparently assumes that all service station jobs result.
