Why a cash-index forecast starts by looking at futures.
Market-microstructure research supports a narrow claim: futures are often an earlier information venue.
New information often reaches index futures before it is fully reflected in the cash index.
That is the piece of published evidence Graham Says relies on. The literature does not hand the project a closing-level forecasting model; it provides a reason to look at futures as a pre-open information source.
What the literature contributes.
1 · Futures have historically led cash index movements
Kawaller, Koch and Koch (1987) found S&P 500 futures movements leading cash-index movements at minute frequency. Stoll and Whaley (1990), after accounting for infrequent stock trading and bid-ask effects, still found a short futures-to-cash lead on average.
2 · Lower trading costs help explain why
Fleming, Ostdiek and Whaley (1996) formalised the trading-cost hypothesis: informed traders have an incentive to trade first in the market where information is cheapest to express. Frino and West (2003) found consistent evidence across two futures venues on the same Nikkei 225 underlying.
3 · E-mini futures became a dominant price-discovery venue
Hasbrouck (2003) studied the Nasdaq-100 at one-second resolution and attributed more than 80% of price discovery in his sample to the E-mini contract.
The signal is locked 15 minutes before the cash open.
Graham records the futures observation at 09:15 New York time. The regular US equity session opens at 09:30.