There are lots of definitions.
A commonly used cutoff for "gifted" is an IQ of 130 on a test where the average is 100 and there is a 15 point standard deviation (so, roughly the 98th percentile). This presumably means that a score of 130 in a subtest means giftedness in that area, as well. This score presumably translates to moderately gifted/MG.
The Davidson Institute defines "profoundly gifted" as an IQ of 145 or more (roughly the 99.9th percentile).
Personally, I think of HG (highly gifted) as starting around an IQ of 140. This is roughly the 99.6th percentile and is therefore only ~20% of the gifted population. My understanding is that a 10-point IQ difference is a moderate (i.e. reasonably sized) difference in ability, such as being able to easily learn things that kids/others with IQs around 130 would have to work harder on.
Some people may use a cutoff of 120 (~90th-91st percentile) as "mildly gifted."
Really, it's all on a sliding scale and there isn't much difference between, say, the math ability of someone with a math subtest score of 137 and 140. Though these small differences do seem to have meaning on a population scale.
Last edited by Val; 11/13/13 12:01 PM.
