Given that farmers not exposed to pesticides were not at
an increased risk for PD, the high proportion of farmers
(76%) included in the study sample has indicated the direct
effect of pesticides. However, the PD case-finding procedure
has some major pitfalls: self-reported occurrence of PD is
likely to lead to a considerable amount of underrecognized
and underreported cases of the disease. In fact, the incidence
rates that Ascherio and coworkers1 reported were somewhat
lower than those previously reported in a population-based
study with direct screening of each sampled individual and
the clinical confirmation of those who screened positive.