Listen to the Summary of Tim Harford's The Undercover Economist Strikes Back in 20 minutes. Please note: This is a summary & not the original book. The Capitol Hill Babysitting Cooperative was a group of parents who would babysit for one another, and most of them were members of the congressional staff who worked in or near the U. S. Capitol. With almost two hundred families in the circle, working out who was owed an evening of sitting and who was owing would have been a tricky bookkeeping problem...