Cathy, I understand that they would have to add in the decimal digits since HG seems to start at 99, and PG seems to start around 99.9? Such a difference within that one percentile point.
As mentioned above, MG, HG, EG, and PG have no standard definition. The big problem is that score reports often list the percentile as ">99th percentile" or ">99.6th percentile" etc. So people don't really know the precise percentile anyway (assuming that kind of precision would be meaningful when you take the test ceiling into account.) Current tests are simply not designed to differentiate between these groups (however they are defined) whether the scores are reported as standard scores or percentiles.
If you want to figure out the percentiles from the standard scores you can use this
Score Conversion Table and this
Normal Curve CalculatorFor example, if I have a standard score of 149 for a test with a standard deviation of 15, I can look in the table to find the corresponding Z-score (3.27) Then I can put that into the normal curve calculator to get a cumulative area of 0.9994622 which corresponds to a percentile rank of 99.94622
Have fun with numbers
