Winston,

Why did you omit the telling remainder of that example?



The percentage of runners is # of LTO winners/ Total # of runners.

That does not tell you what field sizes those 5,548 runners competed in.

The average field size for them could have been much less than 69,234/6,678 (~=10) or it could have been much greater.

If the average field size those 5,548 ran in was relatively small then their # of wins should be flattered. Along with the IV.

Yet you ask:



Of course it doesn't mean that. What were the field sizes for those 5,548 runners? Even just the average or total. You do not have any of that information in that formula.

You claim to be

yet you don't seem to realise what erratic effects field sizes could have on them.

mr jfc.
one word answer please.
do you now concede that impact values take field size into account?
Thank you. Winston.

Winston,

I've already given you the answer. I've shown you that Impact Values take no account of field size.

Impact Values try to measure the effectiveness of a group with a certain characteristic.

But the process to determine an Impact Value ignores the field sizes of the races that group participated in.

Amazingly you suggested "% of runners" (for that group) somehow took account of field size. It doesn't.

Here is an example intended to demonstrate how Impact Values can draw the wrong conclusion.

Group A has a certain characteristic that Group B lacks.

Assume that an A and a B compete in races with field size 2.
And that 1 A and 9 ** run in races with field size 10.
There are 100 races with each of the field sizes.

Now if both A and B have the same chance of winning, then As should win 60 (=50+10) of the 200 races.

The 4 totals used to calculate the Impact Value are:

60 = A Wins
200 = Total Wins

200 = A runs
1200 = Total runs

The Impact Value is 30% / ~17%

= 1.80


This wrongly suggests that As should win 80% more than their fair share of races.

In fact both A and B have the same chance of winning, it's just As were lucky is running in a disproportionally high number of piddly races.

Winston, you claim to be very knowledgeable about Impact Values yet never once has it dawned on you that they can have a fatal flaw in disregarding field sizes.

Even after I told you about that flaw, you did not bother to check for yourself but instead clung on to your cherished belief of your self-assessment.

Mr jfc,
your contrived example makes no sense and is irrelevant to this discussion. we are not argue whether impact values good or bad. yet.
those 5548 runners ran in 6678 races. in those 6678 races there were 69234 runners. blind freddy and his dog can see that the 69234 runners is the total field size for those runners. and the average is 69234 / 6678 or approx 10.37
please how can the average field size be anything but 69234 / 6678?
there is old saying which goes "there are none so blind as those who will not see"

anyway, we get off the point. you offered your flawed statistics to try to justify your statement of "significance". nothing you do here has justified the use of that word. your premise that a horse has 3/N chance of running a place in a field size of N is flawed. as mr chrome prince (did not prince become "the artist formerly known as ..... "?) has rightfully pointed out this not consider the relative merit of each horse in each race. you have assign equal chance of running place to every single horse in the race. this is very dangerous assumption.
Thank you. Winston.

mr chrome prince.
you are correct that there is serious flaw with impact value calculation. you are right that it take no account of the actual chance of winning or placing for each horse. mr jfcs figures are equally flawed as he gives 1/N chance of winning a race to every horse in the race and 3/N chance of placing for every horse in the race. he knows this which is why he refuse to answer my question on this point.
Thank you. Winston.

Hi!
I don't want to buy into this argument on either side, but your assumption in this case about the field size being taken into calculation is just wrong.
True the average field size maybe 10.37 but it can be made up of countless variations in field sizes between 2 and 24. (unless you want to include a one horse race as well, they DO happen).

Good luck

Winston,

If my example makes no sense then why can't you identify which figures are nonsense.

My example makes perfect sense and exposes the flaw in Impact Values. And that happens to be the most important part of this discussion.

Once you understand the principles in that example you can then come up with more realistic scenarios where the Impact Value gives misleading results.

It's just that you've been sprung about your self-assessed expertise about this topic and have to resort to one more "value judgement" to try and wriggle out.



You are making the false assumption that every one of those 6678 races has to include at least 1 runner with the characteristics under consideration.

If you look at the other examples on that page you will see:


Note that there are fewer runners with the characteristic (=2,264) than the 3,127 races!

I remind you that my example include As and Beez (for the censor) in every race, but the IV still makes the wrong conclusion.

Now you, of all people, claim that this is getting off the point. Exactly what is the point of your sudden uninvited arrival here, where you pick up on insignificant matters. Then when I trouble to elaborate, you resort to misquoting me. For example there is a massive difference between my "more significant" phrase and your subsequent distortion into "significant" (the absolute).

mr jfc
please do not misrepresent my position. you berate others for doing this and now you do it youself. i have never said that impact values are not flawed. in fact on one occasion i actually state that i believe they are flawed and on another occasion i say that they are not as good as Nicks calculations. i think everyone here who read my statements will know this to be true.

you are trying to argue that your calculation are better than impact values. your calculation is probably better and for the sake of this argument i shall concede this point. it is after all irrelevant.

all you have done so far is throw up smokescreen to hide the fact that three times now you have ignored my assertion that your figures are flawed. they are fatally flawed. you argue all other points other than this becos you know that you cannot argue this point. to suggest every horse has 1/N chance of winning and 3/N chance of placing is just plain silly. your calculation are based on this premise and it is here that your calculation are flawed. ignore fact that impact value are flawed. ignore question of whether your calculation better than impact value. your calculation still based on flawed logic therefore calculation are flawed. even mr chrome prince agree with this.

now let us go back to original question i ask. you did not say "more significant" you said and i quote
"Horses who run 3rd <=0.5L are significantly better than 2nds > 3L."
you said "significantly better". i ask you to justify this and you post flawed figures. when i challenge you on your flawed figures you branch off into "insignificant matter" try to prove your figures better than impact values when the real issue is your figures are flawed.

i think this forum is open forum for all to discuss. i think discussion is good to try to understand nature of things.
why you not want me here mr jfc?
is it becos i do not blindly accept what you say as gospel truth and that i seek to find evidence of such truths?
i think anyone who blindly accept anything that is said on forum such as this is fool.
Thank you. Winston.

mr jfc
in post number 45 did you or did you not say
"Actually I thought there was a significant difference in favour of the one that ran 3rd." (my emphasis)
who is distorting what now?
Thank you. Winston.

Winston,

You are distorting now Winston, just as you did before.

Rather than refer to my actual quote, you found 2 similar ones of mine which you now want to labour.

The actual exchange in question was:





You quoted me then immediately distorted my "more significant" phrase into "significant" which has a distinctly different connotation.


As to the other material regarding "more significant", I already answered you.

For 2 samples of ~10,000. The wins/fair share indexes were 52.4% versus 31.5%.

I consider those figures significantly different.

If you don't agree with my conclusion that doesn't concern me. Feel free to bet that way.