What Different IQ Scores Mean

Cautions for Interpreting IQ Scores

Normal Distribution & IQ Scores

Low IQ & Mental Retardation

High IQ & Genius IQ

IQ Scores & Ratings

What is a good IQ score?  What is a high IQ score?  What is a low IQ score?  These are common questions, particularly after someone finds out their score from an IQ test.

Lewis Terman (1916) developed the original notion of IQ and proposed this scale for classifying IQ scores:

• Over 140 – Genius or near genius
• 120 – 140 – Very superior intelligence
• 110 – 119 – Superior intelligence
• 90 – 109 – Normal or average intelligence
• 80 – 89 – Dullness
• 70 – 79 – Borderline deficiency
• Under 70 – Definite feeble-mindedness

Normal Distribution & IQ Scores

The properties of the normal distribution apply to IQ scores:

• 50% of IQ scores fall between 90 and 110
• 70% of IQ scores fall between 85 and 115
• 95% of IQ scores fall between 70 and 130
• 99.5% of IQ scores fall between 60 and 140