The standard index is a measure used in finance to determine an investment's performance. It compares the return on an investment to that of a benchmark, such as the S&P 500 or other stock market indices. The standard index is calculated by taking the average return of the investment being measured and comparing it to the average return of the benchmark over the same period of time. If the standard index equals 1, then the investment performed exactly in line with the benchmark; if it's greater than 1, the investment outperformed the benchmark; and if it's less than 1, the investment underperformed the benchmark.