in this case Z can represent economic, labor, or non-economic immigration factors.
This paper substitutes two Z variables into equation (7) namely, unemploydiffij
which is the difference in national unemployment rates in destination country and
source county, and goveffectivenessij which is from the Worldwide Governance
Indicators 2013 and is the ratio of government effectiveness index between
destination and source countries. The humanj
variable is the level of human capital
(secondary school enrollment) in source country.