T Auto,

Your definition of "efficient" a little skewed and Becareful has expertly explained just how the market is in fact efficient. It's about assessing the win rates against the probability as indicated by the prices....not that every favourite should win.

Gettingitright, your point that because the market is set to >100% means you will lose across all odds ranges is spot on. The loss is not exactly the ame though, as Becareful pointed out, because there is a favourite - longshot bias in our betting markets. You will lose less if you backed every even money favourite than you would if you backed every 2/1 shot, which would lose less than backing every 5/1 shot etc. This characteristics exists world wide and there are all sorts of theories to explain why, too detailed to discuss here.

It's also true that while the market is efficient on average across all races, there is natural variation to that, call it standard deviation if you like. The task of a punter is to identify the specific instances where the market is inefficient (the positive variations) and bet accordingly. In markets set to anything more than 100% it's the only possible way to win.

It's kind of ironic that this is the most logical of all winning principles but the one least understood by punters.