A population of numbers (a list of numbers) is said to have a nearly normal distribution if the histogram of its values in standard units nearly follows a normal curve. More precisely, suppose that the mean of the list is μ and the standard deviation of the list is SD. Then the list is nearly normally distributed if, for every two numbers a < b, the fraction of numbers in the list that are between a and b is approximately equal to the area under the normal curve between (a − μ)/SD and (a − μ)/SD.