Explain the problem of double counting in estimation of national income by value-added method

Explain the problem of double counting in estimation of national income by value-added method.

While estimating the National income, the value of only final goods and services is included. However the prolem of double counting arises when value of intermediate goods is also included along with the value of final goods. So, double counting means a counting of an output more than once in the process of various of stages of production.