Updated
Whether to take the morning price or wait depends mostly on the price itself. Across 308,872 GB and Irish runners over three years, horses priced under 3.0 in the morning tended to hold or shorten by the off — waiting risked losing the price — while everything from about 4.0 upward drifted on average, and 21.0+ outsiders drifted hardest (median +22%). But the spread around those averages is enormous, so the base rate is a guide, not a system.
Most money arrives close to the off, and recreational money concentrates on fancied horses — pushing their prices in and, mechanically, pushing the rest of the field out. The result is the classic pattern: the front of the market firms, the back of the market drifts.
The median says yes, the tail says be careful. The outsider that shortens is usually the one with stable money behind it — exactly the bet you most wanted at the early price. Waiting earns a few extra points most of the time and costs you the price precisely when the bet was best. That asymmetry is why a base rate is not a timing edge.
Substantially. With BOG, taking an early bookmaker price is one-way: if the SP is bigger you get the SP, if it's shorter you keep your price. Where BOG applies, taking the early price on anything you fancy dominates waiting — the drift risk is absorbed by the bookmaker.
Racing Alpha publishes the full table free at /price-drift — shortened/drifted percentages, median move and the typical range for nine price bands, flat and jumps separately, from three years of Betfair data with thin morning markets excluded.
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