The use of country and factor-speci

The use of country and factor-specific efficiency factors in meta-production
functions can be easily extended to the case in which they are variable rather
than constant over time. In fact, for the Cobb-Douglas model, if the
efficiency factors are of the constant exponential form, then a second
differencing of the production function will eliminate the country-specific
technological change effects. In general, with a sufficiently long time-series
and a flexible functional form, one can estimate country and factor-specific
time-varying efficiency factors which may further depend on other environmental,
institutional and policy variables simultaneously with the metaproduction
function. For example, the efficiency factor for land may be
assumed to depend on the climate of the particular country.