IMMIGRATION POLICY AND THE AGRICULTURAL LABOR MARKET: THE EFFECT ON JOB DURATION

Next, treatment of completed and uncompleted employment spells of workers should be
considered. Hashida and Perloff (1996) and Tran and Perloff (2002) use only completed spells,
while Emerson and Napasintuwong (2002) use only uncompleted spells. There are further
distinctions in how spells have been defined in the literature. Hashida and Perloff (1996) define
the duration variable as the average duration of completed spells of farm employment by a
worker. Tran and Perloff (2002) work with employment transitions among three types of spells:
agricultural employment, nonagricultural employment, and unemployed or abroad. They
recorded a transition on a monthly basis over a two-year work history among the three above
types of spells without regard to employer. Emerson and Napasintuwong (2002) define the
duration variable as the number of years reported working in U.S. agriculture. At this point our
estimation uses multiple completed spells per worker of agricultural employment at a single task.
Our current definition is closest to the one used by Hashida and Perloff (2002), and specifically
addresses variations in individual job duration by farm workers.

Methodology

The basic structure of the Heckman-type two-stage method is specified with the ordered
probit model for the first stage and the duration model for the second stage. The ordered probit
model is used to explain the legal status of worker i as a function of the individuals’ demographic
and policy variables(denoted as vector x_i). A foreign-born worker’s legal status (Ji) takes on four
values: 0=unauthorized, 1=authorized, 2= permanent resident (green card holder), 3=citizen.
With the familiar argument of latent regression (Greene 2003), we can assume that an unobserved
variable Ji^* is censored as follows:

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