Here's what we've been talking about in practice. The first four home have an insane rating, decent horses as they are it is implausible that the best 4 performances (5 of the top 20) over the course of nine years all came in one race.
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So I've looked at a formula which will identify outlier races and where that occurs, it will re-assess the going rating for that race and it will apply to the race in question. Its quite complicated, but it doesn't actually identify a large number of such races, and it has the reverse effect of upgrading some performances too.
So following rating adjustments, this is the top 20 for Dundalk, spot the differences now
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And here is the original list with a new rating down the right hand side. It's pleasing that my -33 is actually just 1 different from that
TheBluesBrother identified.
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Another race that looked wrong was this one below, it seems to have over-rated quite a number of runners so the performances of these are adjusted down to the tune of 22lb.
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This race also read as an outlier, but in the opposite direction, the actual figure not flattering the performances at all, and it has upgraded the performances from this race. So in reverse order, the race was won by Queen of the Sand and its rating of 38 was considered to more realistically merit a 54. The remaining races at that meeting received the normal going allowance.
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In this race, a three runner one, it did not figure in the going allowances for the meeting and it meant this race received its own upgrade of 40lb. On my figures, Panama Hat had previous run to 73 on 19/08/2014, so its not a ridiculous proposition.
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So the races that are isolated are those where most horses have made no contribution to the actual going allowance for the meeting, as their Z-Scores sit outside -1.5/+1.5. It only amounts to around 300 horses of the 30 odd thousand. Some might say its criminal to not take the face value rating but if there's a way of getting rid of Primo Oumo (down to 65) from the top of the list and most other ratings remain intact it might not be a bad thing.
This is bearing in mind I am experimenting - still.