1. Graphing -“Some pictures are worth a thousand words”!!
Presenting Scientific Data
Scientists accumulate vast amounts of data by observing events and making measurements. After scientists organize data in
tables, they may display the data in a graph. A graph is a diagram that shows the relationship of one variable to another. A
graph makes interpretation and analysis of data easier. There are three basic types of graphs used in science - the line graph,
the bar graph, and the pie graph.
What is a graph?
Graphs are one of the most useful ways to organize and analyze quantitative data. Graphs show patterns, communicate
information, and allow scientists to make predictions that can support or disprove a hypothesis. Graphs help us see
information better. When we have a lot of information, graphs put all the information in one place so that we can see it
quickly and refer to it more easily. The visual characteristics of a graph make trends in data easy to see. When you use
graphs, think carefully about the conclusions you can draw from them. You want to make sure your conclusions are based on
accurate information and that you use scales that help make your graph easy to read. One of the most valuable uses for graphs
is to show data collected during an experiment. The graph shows your results.
Types of Graphs:
Line graphs
In laboratory experiments, you will usually be controlling one variable and seeing how it affects another variable. A line
graph is used to show the relationship between two variables. The variables being compared go on two axes of the graph.
You can do a number of things with the information in a line graph:
 You can determine how a variable changes over time,
 Given one variable, the other variable can be determined,
 You can show trends in the data, and
 You can make predictions about data that is not recorded
Setting Up a Line Graph, you must first identify the variables to graph
Determine the Independent Variable
The independent variable (aka the manipulated variable) is the one that is changed by the scientist. In an experiment there is
only one independent variable. As the scientist changes the independent variable, he or she observes what happens. In a line
graph, the independent variable always goes on the x-axis.
Determine the Dependent Variable
The dependent variable (aka the responding variable) changes in response to the change the scientist makes to the
independent variable. The new value of the dependent variable is caused by and depends on the value of the independent
variable In a line graph the dependent variable always goes on the y-axis.
Figure 1: an experiment has two variables, time and temperature. Time is the manipulated variable because you chose the
time intervals to take the measurements. The temperature is the responding variable because its value depends on what
happens in the experiment. A person who has never seen your experiment can look at the graphs above and know what took
place.
Figure 1
Bar graphs
Bar graphs are similar to line graphs. They compare data that do not continuously change. In a bar graph, vertical bars show
the relationships among data. Bar graphs make it easy to compare data quickly. A bar graph is useful when you want to

2. compare information collected by counting, or similar data for several individual items or events. Use a bar graph if you are
not looking for trends (or patterns) over time and the items (or categories) are not parts of a whole. A bar graph makes it easy
to see how the data for one item compares with the data for another. A bar graph might be appropriate for comparing
different trials or different experimental groups. It also may be a good choice if your independent variable is not numerical.
To make a bar graph, set up the x-axis and y-axis as you did for the line graph. The data is plotted by drawing vertical bars
from the x-axis up to a point where the y-axis would meet the bar if it were extended. Bar graphs can be simple, double or
divided bar graphs. Figure 2 depicts the type of data you might use to generate a simple bar graph.
Figure 2
Pie Graphs
Pie graph uses a circle divided into sections to display data. Each section represents part of the whole. All the sections
together equal 100 percent. Pie graphs (aka pie charts or circle graphs) are an easy way to visualize how parts make up a
whole. If you think of a pie cut into pieces, you have a mental model of a pie graph. For example you could use a pie graph if
you need to compare different parts of a whole, where there is no time involved and there are not too many categories. Figure
3 is a pie graph that describes the energy consumption in the United States. The entire circle represents the types of energy
used in the United States. Each "slice" of the pie represents a percentage of each type of energy being used.
Figure 3
How do I make a graph without using paper?
Microsoft Excel tutorial: http://iqa.evergreenps.org/science/resources/graphing/xlgraphs.htm
Web-based graphing tool: http://nces.ed.gov/nceskids/createAgraph/default.aspx
Practice