The difficulty in the farm worker duration model is that it has two sources of
inconsistency. The observations are censored in the sense that the duration of a person with a
particular legal status is observed only if the person has that status. Some observations are also
censored in the sense that they are uncompleted. On the other hand, the legal status model
(ordered probit) does not have restriction on observations, so that it should be a consistent
estimator. The above method takes care of the selection bias by using correction terms for the
mean duration. The current estimation approach drops uncompleted spells from the data set,
introducing an unknown extent of bias in the estimation. However, given the size of the data set,
the bias is believed to be minimal.
Data
The data used in this study are obtained from the National Agricultural Workers Survey
(NAWS) (Office of Assistant Secretary for Policy). We used the study period from 1989, when
the NAWS was first available, to the most recent year, 2004. This section will describe the
definitions of each variable we used in our model.
Legal status is a discrete variable ranging from 0 to 3. Status 0 = “unauthorized” workers
means that the worker is undocumented (did not apply to any legal status or application was
denied) and also includes those who had no work authorization even if they were documented.
Status 1 = “authorized” workers or documented workers; these workers must have a work
authorization and may fall into any of the following status: having border crossing card/commuter
card, with pending status, or temporary residents holding a non-immigrant visa. Status 2 =
“permanent residents or green card holders” who have the right to reside and work in the U.S., and
status 3 = “citizens” who are a citizen by birth or a naturalized foreign born citizen.