Real S&P500 Index Started in 1957

The real S&P 500 started on February 27th, 1957.  The data before that can not be used for return calculation purposes since the index was not 500 stocks.  It has very small numbers of stocks called 'Composite Index'.  Starting in 1957, we have 60 years data to use for calculating the returns which is around 10% average annually.