As the name implies, the S&P 100 consists of 100 companies from a wide range of industries. The index is a sub-set of the S&P 500. The Standard & Poor's 100 Index is usually considered the benchmark for U.S. equity performance and liquidity. The S&P 100 is not just a list of the largest 100 companies. It is an index of 100 of the most widely held U.S.-based common stocks, chosen by the S&P Index Committee for market size, liquidity, and sector representation. According to the Index Committee, "Leading companies in leading industries" is the guiding principal for S&P 100 inclusion. While widely traded international companies are included, the Index Committee recently announced that only U.S.-based companies will be added in the future.
基期是什么时候?基期基数是多少?