Range is NOT the best method of measuring dispersion because it considers only the

Analyze the question: It asks why the range is a weak measure of dispersion (spread). The answer must describe which values the range actually uses.

Explain the concept: Dispersion tells us how spread out the values in a data set are. The range is the simplest measure:

Range = Highest value − Lowest value

Work through it: Take the data set: 5, 8, 9, 10, 12, 40

• Range = 40 − 5 = 35
• The value 40 is an extreme outlier. It stretches the range, even though most of the data lies between 5 and 12.

Notice that the range ignores every value in between. It uses only the largest and smallest values, which are the two extreme numbers. So it:

• is heavily affected by outliers
• does not show how the other values are distributed
• gives no information about how the data clusters around the average

Now check the options:

• A. First number: wrong, the position in the list does not matter.
• B. First two numbers: wrong, the range does not use the first two values.
• C. Frequently occurred number: this describes the mode, not the range.
• D. Middle number: this describes the median.
• E. Two extreme numbers: correct, since the range uses only the highest and lowest values.

Tip: Remember "Range = Rough." It looks only at the two ends (the extremes) and ignores everything in between. Better measures of dispersion, such as variance and standard deviation, use all the values.