At the end of the day every horse, in every race, has some chance of winning and, equally, every horse has a chance of not winning.
Racing is a percentage game where every horse has a chance of success and there is no such thing as a 'dead cert' or a 'no hoper'. We've seen horses at 999/1 on Betfair (the largest price possible) win and horses with microscopic odds lose.
Given that everything has a chance of success, no matter how big or small it is, then it is possible to tie a figure to a horse's chances.
We at UK Horse Racing have tried to do that and we're proud of our achievements as a long back study of our value figures shows that we've more of less got it pretty much spot on.
When we say that a horse has a 4/1 chance of success we mean that one time in five, i.e. 20%, this horse ought to win. This is our value price which we put on a horse and for those who do what we call value betting then the important thing is to get a better price than this value price. When one does that then we're getting a good risk:reward price for the bet.
The value figure is placed in the ratings in the pentultimate column, next to the forecast SP, and within the daily CSV files.
On a personal note, I never back anything unless I can match, or beat, the Value price.