The Keynesian multiplier concept ignores crucial opportunity costs

The Keynesian multiplier is a concept embedded in macroeconomic thought, policy, textbooks, and widely taught in classrooms. Apparently the only controversy is its empirical size. Is the multiplier a large positive or near zero or perhaps even negative? Most empirical studies have found an impact multiplier that is positive but near zero and a long run multiplier that is larger. From an Austrian perspective, there are several problems with the multiplier concept and the research on it. Coupled with the fact that the concept fails to fully take into account opportunity costs, the multiplier concept has no basis in logic and should not be considered in policy.