The GDA in Denver has done some studies on this; but it is all very limited.
Now, it is important to understand that all of this will give, at most, are statistics. My favorite example for this is that "men are in average higher than women" is a true statement inferred from statistics. I am taller than many men, and that doesn't contradict the statement, nor it disproves it. In the end, you can't predict anything for one particular individual.
Without all formally having been tested, I am sure that 3 out of the 4 of us siblings are gifted; probably one HG. I am pretty sure our spread is much more than 10 points.
My youngest dd's number is an underestimate (English is her 2nd language), but it looks like it is going to be similar to her sister's (with likely the older one stronger in performance). They are both in that gray zone, between HG and PG, HG according to some definitions, PG from Davidson's definitions. That is where their dad is, his IQ scores from long ago were a few points shy of the PG mark. In our case, it looks like both are closer to their dad than to mine (MG).
But then again, this is all anecdotal.
