3dayz wrote:
Just the scientific side of me looking at the other side of the correlation, but what if it is that the larger more successful farms(who most likely have better stallions/mares and better quality foals) all generally start their horses as long yearlings/2yr olds? And then those with less resources and maybe less quality foals, wait longer?


That isn't really the case. If anything a larger farm is more inclined to have a richer owner and therefore be in less a hurry to make back in the investment and therefore can afford to wait. Smaller owners and partnerships, which make up the majority of US starters' ownership, usually have more of a financial incentive to start young as they have more pressure to get a ROI and quickly if possible. If anything, this fact means stats taken from only lower level tracks or only higher level tracks might be biased (as lower level tracks might have more people pushing for 2yo starters and of a lesser quality), but they have taken stats from a huge pool of differing tracks Churchill Downs to Zia Park.

I do think you are right though, that are are so many subjective variables that it is difficult to draw meaningful conclusions in regard to statistical studies. Which is why I defer to the opinion of DVMs like Larry Bramlagewho have done medical research in the area. Their findings support that racing 2yos is to their benefit as racehorses.