The Rahn Curve

The Rahn Curve suggests that there is an optimal level of government spending which maximises the rate of economic growth.

Diagram of Rahn Curve

Proponents of the rahn curve tend to use it as a tool to argue that government spending hinders economic growth. For example the Centre for Freedom and prosperity point to empirical studies which suggest that the optimal level of government spending is between 15 and 25% of GDP. [link] That page also shows links to other reports and empirical studies which would be worth investigating. 

Note Government spending in US is approx 37% of GDP, in UK approx 43% of GDP, in western europe some countries have more than 50%

Check out this link for a Rahn Curve education.
See also Big Government.com