THE LABOR SUPPLY OF SINGLE MOTHERS
ones.15 Consequently, our calculations of AFDC benets for those who work may be fairly rough. We will return to this issue in Section VI.
Under AFDC, the Secretary of Health and Human Services (HHS) was authorized to waive specied program requirements to allow states to experiment. This waiver authority was rarely used prior to the late 1980s, but its use accelerated under Presi- dents Bush and Clinton. Between January 1993 and August 1996, HHS approved welfare waivers in 43 states. While states experimented with changes in nearly every aspect of AFDC, many provisions applied to small parts of states or would not be expected to have a substantial effect on the employment of single mothers. We focus on a few types of waiver provisions that were tried in many states. Our main welfare waiver variables are Any Time Limit, which equals one for single mothers in states that imposed work requirements or benet reductions on those who reached time limits, and Any Terminations, which equals one for any single mother in a state in which a welfare case had been terminated under a welfare waiver. Some common types of pro- visions, such as expanded income disregards, have been incorpo- rated in our coding of the AFDC program. Others, such as family caps (which limited the benets for additional children) or in- creased resource limits (which loosened the asset restrictions for AFDC eligibility), likely have small or ambiguous effects on em- ployment and are therefore not included.
In this paper we focus on implementation dates and actual beginning dates of terminations instead of application or ap- proval dates. We also examine a dummy variable for states that applied for a major statewide waiver, in case this indicates a tightening of administrative requirements in a state. These vari- ables are interacted with an indicator for whether a woman has children. In Table I we report the fraction of single women living in states that have applied for or implemented various types of waivers. Very few women were in states that had implemented signicant waivers through at least 1994. The fraction of women in states that had made a major waiver application was much higher, 0.22 in 1992 and 0.85 in 1996.
15. See Fraker, Moftt, and Wolf  and Levine . Other research indicates that few AFDC recipients report their income to welfare ofces [Edin and Lein 1997; Hill et al. 1999].