The increase in a country's national income, or sometimes, its per capita national income. Growth is taken as the basis of advancing human welfare, although in fact there are problems in the measurement of national income (some activities - such as do-it-yourself car maintenance rather than buying the services of a garage mechanic, or transactions in the informal economy - may not take place in a market, or not in a market for which statistics are collected). Moreover, growth in national income should not be equated necessarily with growth in welfare (environmental accounting; welfare economics) (Trevor, 1956).