Standard & Poor's flagship indices, the S&P 500 and S&P 100 are essential benchmarks for analysing the US financial markets. Launched in 1957, the S&P 500 comprises 500 of the largest companies listed on US stock exchanges. The diversity of its components (covering all the main economic sectors) makes it a prime indicator for assessing the overall health of the US stock market. Its performance is often used as a benchmark for investment funds. Less extensive than the S&P 500, the S&P 100 focuses on the 100 largest US companies in the S&P 500 index. This index is representative of the performance of large-cap companies, offering a more targeted view of the leaders in the US market. The S&P 500 and S&P 100 indices are calculated on the basis of free float-adjusted market capitalisation (only shares available to the public are taken into account, thus providing a more accurate measure of the market value of the companies listed). The composition of the S&P 500 and S&P 100 indices is subject to periodic review to ensure that they accurately reflect current stock market trends. Inclusion criteria include company size, liquidity and sector representation.