Sometimes people assume that a graph or a chart is better than
text because it is a picture. A picture is said to be worth a thousand
words, but is it? What is known about reading graphs?
There is a story in every chart or graph
Remember that charts and graphs are telling you a story. When looking
at a graph or a chart, you need to ask yourself, “What is
the story that they are trying to tell?” In working out the
story you are interpreting the chart or graph.
What do you need to know to interpret a chart or graph?
Research[13] has shown that most
people find it easiest to interpret picture charts or pictographs,
followed by circle graphs or pie charts, then bar charts and histograms.
People found line graphs the most difficult to interpret. However,
as was indicated earlier in this section, pictographs are only effective
if each symbol has a stated value.
Interpreting line graphs
Many of the graphs that you look at in the media are line graphs
that are designed to show trends in data. Because people find this
type of graph such a challenge to interpret, the following sections
will examine what you need to know to use such graphs successfully.
Line graphs use two reference axes (‘axis’ is the singular
form of the word). One is vertical, the other horizontal. They provide
reference scales for the data and/or function plotted on the graph.
Note that what we call a line graph (also called a ‘polygon’)
may have curved sections as well as straight sections. Let’s
see how well you are able to read a line graph.
SCENARIO
The following graph tells a story about the growth
of Pam and Maurice.
Answer the following questions about this graph
Read graphs like a sentence
To make sense of many line graphs you need to read them like you
would a sentence, from left to right. Some people find that their
eyes are drawn to something in the graphic display that stands out
so they find it difficult to appreciate or understand the whole
pattern that is shown in the graph. For example, look at the graph
below. This is a graph of the effect of the decline in rabbit populations
on the fox population in inland Australia.
What story is this graph telling you? What do you need to know
to make sense of these data?
I. It helps to know something of the context; i.e. to know that
foxes eat rabbits.
II. Identify what is represented on the vertical axis [Did you
say population?] and what is represented on the horizontal axis
[Did you say time?].
III. You then need to look at the relationship between the two
curves. If you read the curves from left to right, what do you notice?
Did you notice that the fox curve seems to follow the rabbit curve?
This indicates that the fox population is affected by changes in
the rabbit population. This would make sense because you were told
that foxes feed on rabbits.
The three steps to reading a graph
When reading a graph, follow these steps:
I. Read the information that is provided with the graph because
this tells you the context from which the graph was developed.
II. Identify the variables on the vertical and horizontal axes
because this will help you to interpret the graph.
III. Read the graph from the beginning of the curve or curves at
the vertical axis to the end and propose a relationship between
the variables or between the curves.
This will enable you to tell the story of the graph and interpret
trends.
SCENARIO
The following graph represents a gardener's record of daisy growth under a tree that was pruned on the first of November.
