Could a parent’s decision to vaccinate a child depend on a free bag of lentils?  The premise seems implausible:immunization can be a matter of life and death, and a bag of lentils is worth only a dollar. Yet a randomized controlled trial in India showed that a gift to parents of a 1 kg bag of lentils and a set of plates can dramatically raise the percentage of children protected against major disease (Banerjee et al. 2010). Providing a quality immunization camp alone increased the percentage of fully immunized children from 6% to 18%. The addition of the lentil and plate ‘incentives’ raised the figure to a whopping 39%.  How can we explain the outsize effect of a gift of everyday household items? The answer comes from behavioral economics, a discipline that develops more realistic models of the human actor to improve explanation and policy design. This past Monday, Richard Thaler was awarded the Nobel Prize in economics for his work on human irrationality. — blog.wb.org/blogs