Question

in a normal distribution of scores on assessments like those for intelligence, which of the following statements is true about the area that falls between one standard deviation above and one standard deviation below the mean?
a it contains the bottom 50% of the distribution.
b it contains the middle 50% of the distribution.
c it contains the bottom 68% of the distribution.
d it contains the middle 68% of the distribution.

Explanation:

In a normal distribution, about 68% of the data lies within one standard deviation of the mean. This area is in the middle of the distribution. Options A and C mention "bottom", which is incorrect as the area is symmetrically around the mean. Option B has the wrong percentage (50% instead of 68%).

Answer:

D. It contains the middle 68% of the distribution.