Adrian Massey has compiled a massive database of horseracing stats, using every conceivable variable. I have extracted the only really important news for all you gamblers.
Here are the stats for all runners broken down by SP (starting price), the bookies (note, not BETFAIR SP) price just before the race start.
Here' s the news for layers: The good news is that you can practically lay any horse over 2.00 and make a profit over the long haul. The higher the odds, the better... and if you stick to runners 4.0 and higher (circled in red) you can expect 10%+ profit on your lay bets. The bad newsis that those bets need to be at the bookies odds, not Betfair odds, and you will need to pay (up to) 5% commission to Betfair.
Here's the news for backers: The bad news is that you are doomed betting at any bookies prices. The more you bet, the more you will lose over time .... sticking to backing low-priced favourites will only really help you lose slower... worse, you will need to pay 5% commission to Betfair as well. There is simply no edge at those prices. The good news is that if you are betting on runners priced between 20-100% higher on Betfair than the bookies prices, then you should be able to turn a profit over the long-term.
One other curious stat I have circled are the SP Each-Way (place) stats. Layers will see that laying runners in the place market is a pretty good business at bookies odds on runners from 4.0 to 15.0. Then, from 15.0 onwards, it becomes less so (although still good for laying).
So, the key is prices and the expected value over time. If you want to make money on the horses, you have to understand the stats.
summing up the bad news with the good news, Adrian Massey cannot help you.
If you laid against prices, the BF prices and the commission would kill you in the long run.
If you backed on Betfair, theoretically in the long run you would break even, but then you would have commission to contend with.