That site has good examples of how to calculate impact values, but they fall way short in drawing conclusions based on too small a sample size.
5,000 races is a drop in the ocean, I wouldn't be happy with 50,000.
The guys such as the Reads and Bartholemews have sample sizes in the millions.

The reason for such sample sizes is because not all horses handle factors the same way.
For example, some horses carry weight better than others, so if the impact value of topweights were 1.10, you are over crediting or under calculating for some horses than others, so the prices or ratings will be quite out of whack.

Another example is last start winners.
if the impact value is 1.10 for won last time out, and .90 for didn't win last time out, then a last start group1 winner is going to be under credited and a last start hanging rock winner over credited.

There are so many variables, that drilling down within the data is the only way to go, which is why you need huge sample sizes.

Perhaps this is something I might have a crack at in the future, but it's a mammoth undertaking.

Maybe so that it is a relatively small sample, but it is a "start" point.
The problem after that is to get enough data analysis carried out to be more confident in the IV figures.

Iomaca
A reasonable suggestion to start with. Working out how to extract the different classes from the spreadsheet is the biggest hurdle to overcome.
For instance : SC1MW - BM75 - RB71 - Open etc.
Might be able to do it with a Lookup function but I don't know.
Back to the grindstone I reckon.

I would think that there is probably a better way than using all the different States classes. It is a nightmare trying to line them all up, and then we have Opens which aren't really Opens etc etc.

I should have something to contribute forthwith ;)

Chrome Prince
Any input from you is welcome. The problem is, going down this track, in sample size, (I have 32000 races 27 months) and once you have sufficient races to test then there is the chore of analysing all the data. As you say a mammoth task. The question then bears asking "How relevant is it to the next race?" The Eagles won the premiership twice in the early 90s. Could they win again on those results playing the same winning way? Extremely unlikely. The game has evolved and is 12% faster today. From what I am seeing racing is an evolving sport as well. The trainers are learning from the past and applying it to the present. They represent the business side of racing and have a vested interest. They have to be successful, it affects the bottom line. Punting however is a negative sum aside to racing. We fight for an edge over a smaller pot than we collectively contributed and we endeavour to get more out of that smaller pot than our co-contributors. We must then use old trends to recognize new trends. an example is days to last start. With todays training trends <21 days could easily be put out to 35 days. Sorting out class and how the class relates to races is a major edge. I know nothing worthwhile about class but some of these horses seem to be rising or dropping 3 to 4 classes.

So the bottom line is "that we have to start somewhere and talking gets us moving forward". I know that it gets hard for senior posters dealing with newbies but we do bring a different prespective. Many a gold mine has been found by looking at the problem differently. Regards Beton

One way of measuring class is the first 600m time, the last 600m time, the overall race time.

Assuming we stick to 1200m races for the moment for ease of comparison.
What is a better guide race time, pace or finishing speed?

Here are some impact values for horses that won over 1200m within 14 days.

**This is a guide only, you need a lot more data to accurately predict the impact values***

3,248 horse won over 1200m within 14 days
692 won their next start.
21.31% S/R 8.44% loss on turnover at tote prices.

94 horses ran their 1200m in under 69 seconds
26 of them won next start
27.66% S/R

52 horse ran their first 600m in less than 34 seconds
11 of them won their next start.
21.15%

214 horses ran their last 600m in less than 34 seconds
53 of them won their next start
24.77%

The actual race time and last 600m appear to be better guides than pace.

So we combine a fast race time with last 600m fast time (now it's been said that a fast last 600m will result in a fast race time anyway, I disagree, it depends on the pace.)

And here is the proof.

Combine fast last 600m with fast race time and we get
27 qualifiers
7 winners
25.92% S/R

Combine fast race time with fast early 600m and we get
19 qualifiers
3 winners
15.79%

Of course these are tiny sample sizes, but hypothetically these should be the best of the best, and they aren't!
So far the race time is the best indication regardless of pace or last 600m.

So what if we reverse what we believed to be true and look at it mirrored.

3076 horse ran their race in over 69 seconds
649 of them won next start
21.10%

3116 ran their first 600m in greater than 34 seconds
665 of them won next start
21.34%

2958 ran their last 600m in greater than 34 seconds
624 won their next start
21.09%

From this we see the biggest factor is the actual race time (with regards to 1200m races)

The top 10 race times over 1200m resulted in 5 winners next start.
50% strike rate.

And we haven't yet considered weight carried barrier position and most importantly track time or going.

We also haven't evaluated a second placed horse by various margins and given it a rating.

However I believe that times are irrelevant over distance races and sprints are pretty much the only category to benefit from this type of analysis.

Beton,
Don't get me wrong, I fully appreciate what you're trying to do, and you are quite correct, sometimes a different perspective can reveal things that seasoned investigators can't see because it's too obvious.
The best in the business is Mark Read followed by Sean Bartholomew, (at ratings that is).
They have cracked it big time.
I'm left struggling because the classes are a nightmare to line up.
I abandoned ratings and instead use professional handicappers and watch if there is money for their top rated horses.
This is the easiest approach for me.

Hello Chrome Prince
Quote "I abandoned ratings and instead use professional handicappers and watch if there is money for their top rated horses.
This is the easiest approach for me." unquote. Even they get it wrong often.
What chance is there for us plebs? My thoughts are that with computers, too many zero in on the horse that on paper is the most likely winner. All using the same data and similar rating programs. True the majority of these do get up. But the price is slashed. On the TAB there is no way that backing these horses are viable. You have to cull the losers or get better prices. The only real way you are going to get better prices is decide your runner and to lock in the bookie early. Beton