National Output: GDP
Output the most important concept of macroeconomics, refers to the total amount of goods and services a country produces, commonly known as the gross domestic product. The figure is like a snapshot of the economy at a certain point in time.
When referring to GDP, macroeconomists tend to use real GDP, which takes inflation into account, as opposed to nominal GDP, which reflects only changes in prices. The nominal GDP figure will be higher if inflation goes up from year to year, so it is not necessarily indicative of higher output levels, only of higher prices.
The one drawback of the GDP is that because the information has to be collected after a specified time period has finished, a figure for the GDP today would have to be an estimate. GDP is nonetheless like a stepping stone into macroeconomic analysis. Once a series of figures is collected over a period of time, they can be compared, and economists and investors can begin to decipher the business cycles, which are made up of the alternating periods between economic recessions (slumps) and expansions (booms) that have occurred over time. (For more, see High GDP Means Economic Prosperity, Or Does It?)
From there we can begin to look at the reasons why the cycles took place, which could be government policy, consumer behavior or international phenomena, among other things. Of course, these figures can be compared across economies as well. Hence, we can determine which foreign countries are economically strong or weak.
Based on what they learn from the past, analysts can then begin to forecast the future state of the economy. It is important to remember that what determines human behavior and ultimately the economy can never be forecasted completely.