In addition, the pooling of product

In addition, the pooling of production data from different countries which
overlap in time provides the opportunity of taking more than one look at
the technology at any given point in time, thus making it potentially feasible
to identify separately the degree of returns to scale and the level and biases
of technological change and to test such hypotheses as the embodiment of
technological change, neither of which is possible using data from only a
single country.
However, while the use of pooled intercountry data in the estimation of
the meta-production function opens up new opportunities, it also leads to
new problems. The first problem is the non-comparability of data, caused by
the possible existence of intercountry differences in the definitions, measurements,
and qualities of the outputs and inputs. For example, in agriculture,
the composition of output, say, between crops and livestock, may be very
different across countries. The definition of a labor day may be different
across countries. The intrinsic quality of a hectare of land may be different
across countries and its actual efficiency may differ even further depending