Statistical measure designed to show the change of one or more related variables in time. Stock indices measure the performance of a selection of stocks representing a portion of the overall market. The components can be weighted acording various criteria (e.g. Market Capitalisation, Free-Float Market Capitalisation, price-weighted...) and the indices can be calculated as price indices or on a "total return basis" to include the reinvestment of dividends paid. Stock Indices are often used as benchmarks for actively and passively managed investment funds and as underlyings for derivative products.