Deep Store

Robert Shiller's monthly S&P Composite price series, reconstructed back to January 1871. The modern S&P 500 was only created in 1957; Shiller's series uses earlier Standard Statistics and Cowles Foundation data to extend the record.

Why it matters: For multi-decade valuation work, this is the only practical long history of US equities. It's the denominator in Shiller's CAPE and the basis for most long-run equity return studies.

How to read it: Nominal monthly closing price. For real (inflation-adjusted) prices, divide by CPI and multiply by a base CPI — but for most uses, just look at percent changes over long windows. Not a real-time data source — monthly, with a ~1-month lag.

Caveats: This is a reconstructed series for the pre-1957 period, with methodological limitations. Different price indexes used in different eras can introduce small discontinuities.