Educational Psychology / Unit 8 EDP 0705 worked example, 60 to 90 seconds
Ratio and Deviation IQ
The idea
The original intelligence quotient was a ratio: mental age divided by chronological age, multiplied by one hundred. A child whose mental age matches her age scores exactly one hundred; a child ahead of her age scores higher, and a child behind scores lower. The modern deviation IQ works differently. It places a score by its position among same-age peers, on a scale set so the average is one hundred and the standard deviation fifteen.
In practice
Worked example: an eight-year-old with a mental age of ten has a ratio IQ of ten divided by eight, times one hundred, or 125. On a deviation scale, the question becomes how far above the average of other eight-year-olds the child scored: a score of 115 means one standard deviation above the mean.
Where people slip
Both kinds of IQ center on one hundred, but they are computed differently: the ratio compares ages, while the deviation compares a person with peers of the same age. Modern tests report deviation scores.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
Something wrong in this lesson? Flag it · Sources for Educational Psychology