Scott Sumner, of Bentley University talks with EconTalk host Russ Roberts about interest rates. Sumner suggests that professional economists sometimes confuse cause and effect with respect to prices and quantities. Low interest rates need not encourage investment for example, if interest rates are low because of a decrease in demand. Sumner also talk about possible explanations for the historically low real rates of interest in today's economy along with other aspects of monetary policy, interest rates, and investment.