The idea of flows of goods and services, of money incomes and of expenditures is fundamental in the presentation of the national income statistics, and also to their understanding. 'The value of physical increase in stocks and work in progress' is the change in the quantity of stocks and work in progress held by private and public businesses. Measurement from the output side consists of adding up the net outputs of all firms, farms and productive enterprises. The annual income and expenditure statistics are published first in Government White Papers in the April following the year to which they refer and provide an important part of the information upon which the United Kingdom Government bases its economic policy for the succeeding year. A change in the value of output reflects changes in prices as well as changes in volume. The most obvious difference between the old and new indexes is the difference in weights.