The Index is designed to measure the performance of health care companies included in the S&P 500 Index. The S&P 500 Index is designed to measure the performance of the largest 500 companies listed and domiciled in the U.S. The Index includes health care companies in the following industries according to the Global Industry Classification Standard (GICS) as health care equipment & supplies, health care providers and services, health care technology, biotechnology, pharmaceuticals, and life sciences tools and services. These companies are then weighted based on market capitalization. The Indexs composition and the assigned weights are reevaluated every September with additional weight adjustments in March, June, and December.