The favourite-longshot bias is one of the oldest and most stubborn findings in betting markets: longshots are systematically worse value than favourites. Bettors overpay for the dream of a big payout, and bookmakers — knowing this — load a disproportionate share of their margin onto high odds.
The sizes are not subtle. Across decades of studies, heavy favourites return a few percent below fair value, while extreme longshots can cost bettors 20% or more per bet. A 15.00 outsider quoted by a soft bookmaker might carry a true probability closer to odds of 20.00 — you are paying a hidden fee of a quarter of the price.
This has a practical consequence for reading any naive value model: divide a market's overround equally across outcomes and longshots will constantly look like value when they are anything but. Serious devigging must remove margin proportionally more from the outsiders — ours does, and it kills most of the phantom edges cheap models flag on high odds.
It also explains a tipster classic: the accumulator of longshots. Every leg quietly overpriced against you, multiplied together into a ticket whose advertised payout wildly overstates its worth. The dream is real; the price of the dream is rigged.
See how we apply this on every match in our methodology. Methodology →
The systematic overpricing of longshots: bettors overpay for big odds, so bookmakers shade those prices and load more margin onto them. Across our data, outsiders win less often than their implied probability suggests, while short favourites are priced closer to fair.
It means blindly backing outsiders loses more than blindly backing favourites — in our 1,329-bet simulation, always backing the outsider returned −10.2% against −3.6% for favourites. Neither is a winning strategy; the bias is a reason to devig properly, not a system.
Bookmaker margin (vig) and devigging Why win rate misleads Fair odds
See these ideas at work in our public track record — every call logged before kick-off, losses included.