Measuring Usability Homepage
Quantitative Usability, Statistics & Six Sigma by Jeff Sauro



May 2, 2008 | asked by Kay :

Question : Find the probability that a randomly selected adult has an IQ that is less than 130

Answer :

Since you didn't provide me with the mean and standard deviation of IQ scores, I'll use round numbers which should be close. I'll use a mean of 100 and SD of 15. A score of 130 is 2 standard deviations above the mean. Using the properties of the normal curve (for one-tailed-area) we know that's higher than around 97.7% of scores. You can use the z-score to percentile calculator and enter 2 and select 1-sided area. You can also see this visually in the interactive graph of the standard normal curve. Change the mean and standard deviation to 100 and 15 and look at the one-tailed area graph.


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IQ Score3
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