Several groups of experts at CAP, at Glass's Guide and a few other places make predictions based on the past behaviour of prices of a brand and model, adjusted by what they consider to be value enhancing features of the new models. But it's all thrown into chaos by the fact that residuals are based on new car list prices, yet new cars can be bought at anything from a 40% discount to a 20% premium due to the number of optional extras specified. That makes the average residual for something like an Audi A6 a lot higher than for a Mondeo, but anyone who bought a Mondeo at a 30% discount would probably lose a lot less hard cash over 3 years than someone who over-specced an A6.