We will now go over a few ways to describe the spread of data. The
easiest way to describe the spread of data is to calculate
the range. The range is the difference between the highest and
lowest values from a sample.
Example
Let’s assume that the following data
points represent the number of fire over 200 acres on a forest over
the last ten years.
3, 3, 4, 6, 7, 9, 10, 11, 11, 12
The range of fires over ten years is then equal to 12 – 3
Or 9 fires over 200 acres.
You can see that the range is very easily calculated. However,
since it is only dependent upon two scores it is very sensitive to
extreme values. The range is almost never used alone to describe the
spread of data. It is often used in conjunction with the variance or
the standard deviation.
Example
Let’s try an example together, the following data shows the total
surface fuel loading for 10 stands in a watershed. We want to get an
idea of how much variation there is in these stands so we will begin
by calculating the range of our data.
Total fuel loading on 10 sites in tons per acre:
5.3, 6.4, 15.7, 11.8, 7.9, 26.5, 18.2, 11.3, 9.4, 10.5
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