Which British economist developed the concept of the multiplier effect?

Richard Kahn developed the multiplier effect: an initial change in spending can produce a larger total change in national income.

Kahn presented the idea in a 1931 article on the relationship between domestic investment and unemployment. He showed that government or private investment could raise employment directly and indirectly, because newly employed workers spend part of their income, creating income for others.

John Maynard Keynes later incorporated and popularized the investment multiplier in The General Theory of Employment, Interest and Money, published in 1936. This connection often causes confusion, because Keynes is closely associated with the multiplier, but Kahn is credited with developing the original concept.

The size of the multiplier depends on leakages such as saving, taxation, and imports. A larger marginal propensity to consume generally produces a larger multiplier, while substantial leakages weaken the effect.