The Pew Charitable Trusts developed an approach to analyze the clean energy economy of the US. The approach provides a framework to track investments, jobs, business growth over time. It defines a clean energy economy as one that generates jobs and businesses through clean energy production, energy efficiency, reducing emissions, and conserving resources. The US clean energy sector has grown due to various state and federal initiatives and incentives. Jobs in this sector have increased significantly between 1998-2007 especially in energy generation.