Gross Domestic Product (GDP) can be estimated in three ways which, in theory, should yield identical figures. They are
(1) Expenditure basis: how much money was spent,
(2) Output basis: how many goods and services were sold, and
(3) Income basis: how much income (profit) was earned.
These estimates, published quarterly, are constantly revised to approach greater accuracy. The most closely watched data is the period to period change in output and consumption, in real (inflation adjusted) terms.