A purchase index is a statistical measure used to track the level of consumer spending on goods and services within a specific market or industry. It is calculated by comparing the current level of purchases to a predetermined base period, typically using a percentage or numerical value. This index provides valuable insights into the overall health and trends of a market, allowing businesses and investors to make informed decisions about their purchasing and investment strategies. A high purchase index indicates strong consumer confidence and a thriving market, while a low index may suggest a decline in consumer spending and a potential economic downturn.