A statistical approach to HCA

[killer_deep]

Hello All,

I''ve read several posts that suggest that HCA should be used as a tool to eliminate bad options, but not to choose a single good one. This little rule is always accompanied by a warning that there are diamonds with poor HCA scores that are good performers, and diamonds with excellent HCA scores that are poor performers.

My question is this: How often does each of those scenarios actually occur, out of 100 diamonds?

That is,
(1) Out of 100 round diamonds with excellent HCA scores (1-2), how many are poor performers?
(2) Out of 100 round diamonds with poor HCA scores (3+), how many are good performers?

I''m just looking for rough estimates, especially from the experts on this forum that have handled dozens of diamonds. The reason being that if I have to choose a diamond sight unseen, I''d like to know the odds of choosing a well-performing diamond based on HCA values.

Thanks!
S

 

[neatfreak]

I think it's rarer to have a stone that scores well on the HCA be a poor performer than vice versa, there are some beautiful stones occasionally that get poor HCA scores. The only time I would be hesitant to trust the HCA is if it gets a low score on the HCA, but falls outside of GIA and AGS excellent/ideal ranges. I've seen this a few times, and I would be hesitant with a stone like that.

BUT if it falls inside the AGS ideal range as well as a low HCA score? I personally haven't heard of or seen a stone that was a poor performer with that combo. So I would say it is pretty rare.

Just buy from a trusted vendor who can provide pictures and an idealscope or ASET image and you'll know what you are truly dealing with. That is the best way to make sure you are buying a great stone even sight unseen.