Utilization of the aggregation concept applied in economics has been a traditional way of describing the state of an economic system and of predicting the future economic conditions. In addition, certain aggregate variables have also played a crucial role as indicators of the business cycle. Quick examples would be the price index, the productivity changes, the industrial production index, GNP, and so on. The methods of aggregation could be either simple summations, like GNP, or sophisticated weighted average, like the price index.