[llampx]

Right, there was an index in place during the Great Depression for sure. From wikipedia: https://en.wikipedia.org/wiki/S%26P_500

History

In 1860, Henry Varnum Poor formed Poor's Publishing, which published an investor's guide to the railroad industry.[20]

In 1923, Standard Statistics Company (founded in 1906 as the Standard Statistics Bureau) began rating mortgage bonds[20] and developed its first stock market index consisting of the stocks of 233 U.S. companies, computed weekly.[1]

In 1926, it developed a 90-stock index, computed daily.[1]

In 1941, Poor's Publishing merged with Standard Statistics Company to form Standard & Poor's.[20][21]

On March 4, 1957, the index was expanded to its current 500 companies and was renamed the S&P 500 Stock Composite Index.[1]