Although arguably a methodological improvement, matching estimates also have
their own shortcomings. The choice of which variables should be used to match farmers
is not clear. Certain variables like the age of the household head, along with experience
or educational attainment, are arguably exogenous, but other variables like farm size,
specialization or diversification of production, the legal status of farm tenure, and value
of assets may be endogenous to the certification process itself. In addition, matching
requires that the omitted factors be observable.