# Interpreting Scores

Converting standard scores to percentile rank

• If the evaluation test scores are reported in standard score, the link above will tell you how to convert that to a percentile rank.  The 50th percentile is average – meaning that half the people will score above, and half the people will score below.  It is important to see the scores in percentile rank, and also to plot on a bell curve to visually see where the strengths and weaknesses are.  Students with learning disabilities typically tend to have a wide scatterring of scores, meaning some will be in a higher range and some will be in a lower range.  For example, my son was in the 99th percentile for verbal ability, but in the 4th percentile for reading.  This is a huge discrepancy.

Normal Bell Curve

• The majority of people (68% of the population) will score around the 50th percentile, and this is considered average.  This is the peak of the bell curve.   34% of the population will score within 1 standard deviation above the 50th percentile, and 34% of the population will score within 1 standard deviation below the 50th percentile.
• 28% of the population will fall between 1 and 2 standard deviations, so 14% of the population will be between 1 and 2 standard deviations above the 50th percentile, and 14% of the population will be between 1 and 2 standard deviations below the 50th percentile.
• So a total of 96% percent of the population will fall within 2 standard deviations above (48%) the 50th percentile and 2 standard deviations below (48%) of the 50th percentile.
• Only 2% of the population will fall more than 2 standard deviations above the 50th percentile, and only 2% of the population will fall more than 2 standard deviations below the 50th percentile.