Need for the study of National Income. 11. To measure the size of the economy and level of the country's economic performance. 22. To measure the production of good and services. 33. To trace the trend or speed of the economic growth of our country in relation to previous years and that of other countries. 44. To know the contribution of the primary, secondary and tertiary sectors in the national income. 55. To help government, to formulate development plans and policies, to increase economic growth.