What are the major issues that must be considered in measuring inputs

What are the major issues that must be considered in measuring inputs for regression analysis of production functions?

What will be an ideal response?

ANSWER

How is labor to be measured? Can it be measured in hours, and if not, how can the labor actually used in production be expressed? How are materials to be measured? How are capital assets, which have different rates of depreciation and input intensity, to be measured?