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Lesson 3: Basic Descriptive Statistics
6 Describing the Spread of Data < Back | Next >
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.

Letís 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 Ė 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.


Letís 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

Which of the following values is equal to the range of total fuel loadings we found on our 10 sites?

A. 10.6
B. 18.9
C. 7.9
D. 26.5
E. 21.2


1 Overview
2 Intro to Descriptive Statistics
3 Calculating the Mean or Average
4 Calculating the Median
5 Calculating the Mode
6 Describing the Spread of Data
7 Calculating the Variance
8 Calculating the Standard Deviation
9 Graphical Representation of Data
10 The Stem and Leaf Plot
11 Review Questions
< Back | Next >

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