Desirabilty Index is a quantative value that designates how a price is determined in the open market, not just the rawl price. 

When we look at a book or more realistically, MMR, we see a price that relates to a class of car based on the first ten digits of the VIN.  It is a blind price because the specific gear and market conditions of that particular sale can not be veiwed.  Using the "Used Car Invoice Desirability Index" we can dig deeper into how that price or the conditions of that sale were realized.  How many bidders, how hungry they were, who is bidding.  The fact that one buyer that has a customer for a specific car allowed the seller to run him up does not show a trend in the market for that car.  When fifteen bidders follow a car in the lane we know the market is interesting for that type of vehicle.  that does not show up on MMR.  Sitting in the showroom reading MMR the user can't understand the trend of that class of cars.  

Use our Desirrability Index and PAV (potential auction value) and you can feel the vibration of the auction lane.  We are not guessing or doing a statistical algorythum, tossing out the high and low, dividing by two and spitting in the glass tower wind to find the pulse. 

Our prices are rated on the action in the auction lane.  Each car is rated one to five on quality of activity, fed directly to my pricing professionals and adjusted in our system real time when significant market trends and patterns are identified.  And for good measure we check my pacemaker to be sure that I was selling a good Lexus, not watching a blonde, when there is too much activity in our lane  (Only joking. We got to have a little fun, don't we?)