I uploaded some more data today to my website and if you run just favourites (both bet and lay side) you get the following:

There were 49527 horse form lines in the database at this point in time. We update when we get time.
There were 5147 selections for the System
There were 1757 Winners for the System for a strike rate of 34.14%
There were $5165.57 returned for WIN (after 5% commission) which means a Profit or loss of $18.57 or a percentage profit/loss of 0.36%

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The Rules used were : priceRank < 90 and priceRank = 1 and priceLayRank < 90 and priceLayRank = 1

That is showing a 0.36% profit after 5% commission just betting favourites with no filters. Figures taken from 10 secs before scheduled race time and market must be 95%. AUS Markets only.

I'd say that 34% is above the long term average though. Isn't it 33% or even 30% in Oz?

Yes it probably is a bit higher then long term average.
The results are since 8th August 2011 so its only 5 months of data. Still not a bad result for 5 months and over 5000 races.

A number of small observations.

Laying those horses is -10.90% after commission.
This reinforces the fact that although it should be neutral, Betfair favours backers in almost all areas.
Layers are pushing it up a hill.
Backers are starting off with an advantage and are further advantaged by market rules.
Layers start off disadvantaged and are further disadvantaged by market rules.

The TAB average for favourites is 33%, I would guess that the 1% is not a fluctuation, but rather better "picking".
Sometimes you see the inverse of first and second favourite on Betfair compared with bookies and tote.
I also think in the case of equal favourites, Betfair users are more decisive.

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I agree with everything you said Chrome. Betfair is full of people thinking they are better off laying. This is pushing up the prices slightly so that backing can be profitable as the value is on the backing of the selection. I am more and more concentrating on backing betfair selections rather than laying.

7 years of consistent profits, 2 losing days in December, and none so far this year........I'm happy to keep laying.

I ran a favourites analysis on Bet Selector and the NSW Tab favourite won 31.8% of races going back to the start of 2008. However it could be that in cases where the first 2 favourites are very close they could be mirrored on Betfair compared to the tote but you would need to go back the same amount of time to have a accurate figure on that.

I think what you do Mark is different to the majority of layers on Betfair as you frame a book and profit on most races. I was trialing a laying system at BSP and it was losing money so I turned it around to backing those same horses and it became profitable. I would have to agree with Chrome, in my situation the odds certainly favoured my back bets.

mark you apparently make abook ?
interesting.. do you only make a book on a few selected horses in a race
or the whole field .maybe a stupid question but have no idea on how to make a book..any chance you might enlighten me on this or is it an impertinant ask
ty.

Hi nosrad, if you don't ask you don't find out. Nothing secret to what I do. I try to lay every runner and lay them to pay out a different amount depending on their odds and what I think of their relative chances. It's getting over 100% and laying the losers for more which is the tricky part.