The standard deviation is useful because 68% of the scores fall within 1 standard deviation above or below the mean.

Graph description: curve with Mean of 0 in the middle, extending to the left through values -1, -2, and -3, and extending the right through values 1, 2, and 3. The x-axis shows “score” and the y-axis shows “frequency”. The distribution is symmetrical, which means the left side of the graph looks like a mirror image of the right side of the graph.

Just over 95% of the scores fall between +/- 2 standard deviations.