Please ignore my last question. I’ve found the answer now. Most of you will proabably know this already, but I found the following explanation very helpful:
“(N)ot to be confused with the S&P Composite 1500…(t)he composite index is just that, a composition that splices the S&P 500, which started in March 1957, with historical data that included the companies in the S&P 90, founded in 1926, the S&P 233 weekly index dating from 1923, and earlier market data painstakingly gathered by Alfred Cowles. Cowles used family money to found the Cowles Foundation and was responsible for collecting comprehensive US stock data from 1871 to 1930. His magnum opus, the 2nd edition of his Common Stock Index was published in 1939 and is now available online in PDF format.
The S&P Composite has been popularized by Yale Professor Robert Shiller, and an Excel copy of the data, updated monthly, is maintained at his Yale website.”
Cheers