Horses: Accuracy of traded_avg_price vs Betfair PPWAP ?

Hi All

I am recording the traded_avg_price in UK horseracing at 20 seconds after the start time, and later comparing this to Bet Fair's PPWAP(Weighted Average Price of all bets placed pre-off) taken from Bet Fairs price files. In theory these should be about the same, but on average the PPWAP is 15% higher, and sometimes 100% higher than the traded_avg_price.

Does anyone have any insight or ideas about why these numbers are so different?

Perhaps:
a) I need to record traded_avg_price closer to the actual off, since this is on average 3 1/2 mins after the post time.
b) Bet Fairs PPWAP includes BSP bets which moves the price by an unpredictable amount.
c) The numbers are recording in slightly different ways, or representing different things.
d) There is something I am missing.

Thanks

Nick

Hi
I think the first item in your list has a lot to do with it. traded_avg_price will continue updating live in-play whereas PPWAP recorded by Betfair does not include prices after the off. Try recording traded_avg_price at the moment the market turns in-play rather than 20secs in.