A major, but little appreciated, aspect of the caseload decline is that many mothers seem to be leaving welfare without taking jobs. The importance of the various co-residency arrangements for the economic well-being of single-mother families is often underestimated, if not ignored. One reason is that they are embedded within other households and it can be difficult to parse out the patterns involved. The best source of data about families who have left welfare are surveys of former welfare recipients that have been conducted by various states and by the Urban Institute. There is little large-scale, nationally representative data on the incomes of these "co-resident" households that include welfare leaver families. Work requirements and heightened levels of hassle in the process of going on welfare or staying on would be expected to cause mothers to leave welfare for work, even for relatively low-paying work.