Line Graphs
Line graphs compare two variables.
Each variable is plotted along an axis . A line graph has a vertical
axis and a horizontal axis. So, for example, if you wanted to graph the height
of a ball after you have thrown it, you could put time along the horizontal, or
x-axis, and height along the vertical, or y-axis.
As I mentioned before, each type of
graph has characteristics that make it useful in certain situations. Some of
the strengths of line graphs are that:
They are good at showing specific values of data, meaning
that given one variable the other can easily be determined.
They show trends in data clearly, meaning that they visibly
show how one variable is affected by the other as it increases or decreases.
They enable the viewer to make predictions about the results
of data not yet recorded.
Unfortunately, it is possible to
alter the way a line graph appears to make data look a certain way. This is
done by either not using consistent scales on the axes, meaning that the value
in between each point along the axis may not be the same, or when comparing two
graphs using different scales for each. It is important that we all be aware of
how graphs can be made to look a certain way, when that might not be the way
the data really is.
Let's take a look at an example.
In a few years, you might be
interested in getting some kind of parttime job. You find the following line
graph, which plots the minimum wage versus time from Ocober, 1938, to
September, 1997. What kinds of things might you be able to tell from it?
Answer the following questions by
looking at the graph, and then click on Answers to compare
your responses.
1. What was the minimum wage in
January, 1978?
2. When did the minimum wage reach
$3.35?
3. Between what time periods was the
largest increase in minimum wage?
4. Based on your observations of the
graph, make a prediction about what the wage might be in the year 2000.
5. What about the scales used on the
graph might make the data appear differently than how it really is?
