What does Sporting Post's SI stand for?

I've noticed on the downloadable version of the SP race card that there is a "SI" value only on some horses under breeding. What does this mean and what does it indicate? Can any of the breeding or Sporting Post experts help me?

Its not ''SHIT IN'' by any chance.

Lol, I don't think so, because they don't always.

It means "sales Index"

Lets say that the average selling price in a sales was R100 000.00.

If you are looking at a particular horse and say it is 70k, then the SI would be 0.7.
Which means that, that horse's selling price is 0.7 of the average price paid at that particular sale.

SI is Sale Index
It is the sale price of the horse when compared to the average price of horses of the same sex at the same sale.
An index of 1.00 means the price of the horse equalled the average price for the sex at the sale.

Not to be confused with SSI (elsewhere in the form section), which is Standard Starts Index, an American invention.
This reflects the earnings per start of a horse, compared to the average earnings per start for all horses of the same age and sex.
SSI 1.00 means the horse's earnings per start are average.
SSI for runners in a race often gives an interesting view on those with chances.

Also given is the SSI for each race (in the race header), which gives an indication of the strength of the field (it is the average of all SSI's of the runners in that race).

Thanks Karel and east, you are tops(tu) Now can you help zoro find the shit in index (SII) The average of how often a horse might shit in?