A measure of economic activity in a country. It is calculated by adding the total value of a country's annual output of goods and services. GDP = private consumption + investment + public spending + the change in inventories + (exports - imports). It is usually valued at market prices; by subtracting indirect tax and adding any government subsidy, however, GDP can be calculated at factor cost. This measure more accurately reveals the income paid to factors of production. Adding income earned by domestic residents from their investments abroad, and subtracting income paid from the country to investors abroad, gives the country's gross national product (GNP). The effect of inflation can be eliminated by measuring GDP growth in constant real prices. However, some economists argue that hitting a nominal GDP target should be the main goal of macroeconomic policy. This is because it would remind policymakers to take into account the effect of their decisions on inflation, as well as on growth. GDP can be calculated in three ways. The income method adds the income of residents (individuals and firms) derived from the production of goods and services. The output method adds the value of output from the different sectors of the economy. The expenditure method totals spending on goods and services produced by residents, before allowing for depreciation and capital consumption. As one person's output is another person's income, which in turn becomes expenditure, these three measures ought to be identical. They rarely are because of statistical imperfections. Furthermore, the output and income measures exclude unreported economic activity that takes place in the black economy but that may be captured by the expenditure measure. GDP is disliked as an objective of economic policy by some because it is not a perfect measure of welfare. It does not include aspects of the good life such as some leisure activities. Nor does it include economically valuable activities that are not paid for, such as parents teaching their children to read. But it does include some things that lower the quality of life, such as activities that damage the environment.