Changes whenever there is a change in supply. Is determined by income. Is a measure of the response of quantity demanded to changes in price. In a market economy there are a set of factors that should be present if the market is to work effectively and efficiently. This set of factors would include the following.
People act in the social interest and there is mobility of factors of production.
Factors of production act in the social interest and there is good information available about characteristics of goods and services. People act in their own self-interest and there is good information available about characteristics of goods and services. There is good information available about characteristics of goods and services and there are adequate supplies of all resources. There are adequate supplies of all resources and good mobility of resources. One of the benefits of working for an airline is free plane rides.