Gifted Issues Discussion homepage Forums Identification, Testing & Assessment What's a "normal curve equivalent"

And, obviously, I should have read through your correction to your post, too!

If the normal curve equivalent is reported from the normative data and the national percentile ranking is derived from the current data set, they could be significantly different beyond the mappings that aeh gave.

They are usually derived from the same standardization set. But, of course, that may differ depending on the instrument, and even the school system, as some use local norms for the percentiles. That would be a good place to begin asking questions, in the event that the NCE and %ile do not line up as they would be expected to in a normal distribution.

After looking at the linked visual (thanks!), I understand it now. I'm just not sure how that information is useful. I think they are assuming a normal curve when maybe it's not. Her reading score percentile was 95th and NCE was 85th which matches up with the visual, but maybe in our school district 10 percent of kids are in the top 5th percentile nationally (who knows!). It would be more useful to have THAT info. When they qualify kids for gifted programming they are using national percentile rankings which need to be about 95-98th percentile (depending on the program), but I wonder how many kids from the district fit into that.

blackcat, the NCE is not a percentile, so your DDs NCE is an 85, not the 85th percentile. The NCE score of 85 is mathematically equivalent to the 95th percentile. As aeh stated, the NCE score uses a normal distribution with a mean of 50 and a standard deviation of 21.063. So, an NCE of 85 is 35 points above the mean of 50 (85-50 = 35). Therefore, a score of 85 is 35/21.063 = 1.662 standard deviations above the mean. A standard score of 1.662 standard deviation above the mean of a normal distribution IS the 95.2 percentile. So an NCE of 85 is mathematically equivalent to the 95th percentile. This is the same idea as a WISC score of 125 is equivalent to the 95th percentile (since WISC scores have a mean of 100 and a standard deviation of 15).

Hope this helps and doesn't confuse the matter even more

I understand (and understood when I saw the visual), I shouldn't have said 85th in my last post, just "85" or "a score of 85". At first when I saw that report I thought maybe it meant that she was at the 85th percentile compared to other kids in the district. I think it would be really helpful if they included that info. There is a "district average" on the report but it is on a tiny graph with no actual numbers. District average looks like it's slightly above the national average.

I wonder what the purpose is of providing such confusing information.

The NCE is supposed to facilitate comparisons across instruments and across multiple administrations.

I agree that it often would be more helpful to provide local percentiles, in addition to national percentiles. That's usually an option, sometimes for an additional cost per student record.

FWIW, I think that NCE is also more meaningful than national percentiles, particularly if you are dealing with the tails of the distribution. In a similar sense, that local norm provides far more practical information, especially if it is local to your school rather than the district.