The correct answer is a) less than one half of one percent.
IQ scores are designed to follow a normal distribution, with the average score set at 100. A score above 140 is considered to be in the very superior range. According to the standard normal distribution, only about 0.13% of the population scores above 140 on IQ tests. This means that less than one half of one percent of people achieve such a high score.
Here’s a brief explanation:
- Normal Distribution: IQ scores are distributed in a bell curve, where most people score around the average (100).
- Standard Deviation: The standard deviation for IQ scores is 15. A score of 140 is more than 2.5 standard deviations above the mean.
- Percentile: A score of 140 places an individual in the 99.7th percentile, meaning they score higher than 99.7% of the population.
Therefore, the percentage of the population that scores above 140 on IQ tests is indeed less than one half of one percent.