the untreated (ATEU) - are generated as weighted averages of the MTE (Heckman, Urzua and
Vytlacil; 2006a; 2006b):
ATE = E(γi | X =x,Ud =ud)=∫1∆MTE(x,ud)dud
0
(17)
(18)
(19)
(20)
ATET =E(γi | X =x,D=1)=∫1∆MTEωATET(x,ud)dud
0
ATEU =E(γi | X = x,D =0)=∫1∆MTEωATEU(x,ud)dud
0
where the applicable weights based on the propensity score (P) are:
1-Φ Φ
— pP
ωATEτ E (Pi ) ωArEu' 1 - E (Pi )
Data
The data consist of 19,152 foreign workers with complete data from the National
Agricultural Workers Survey (NAWS) for 1989 to 2006. Subsamples reflecting the treated
(those who have obtained legal status; N1=8097) and untreated (those without legal status;
N0=11055) worker groups are specified. Table 1 defines the variables that were used in the
analysis. The variables reflect the demographic characteristics of the crop farm workforce and
certain characteristics of the farm labor market. Dummy variables reflecting the location, time
period of interview, and time period when the foreign workers would have entered the US to live
or work are also included.
Results and Discussion
Table 2 reports the summary statistics for the variables that were used in the analysis. The
treated group comprised 8,097 foreign workers whereas the untreated group comprised 11,055
foreign workers. One of the more interesting findings to emerge from the data is the difference
in time spent abroad by workers of the two groups: workers who are not legalized have much
longer overseas stays than their cohorts who are legalized (5 weeks on average). In addition,
11