Graph Basics

Making a graph usually begins with two lines:
  |                        (You'll have to use your imagination a bit!)
  |                        The vertical line is called the y-axis.
  ------------       The horizontal line is called the x-axis.

Data is information that we gather during an experiment.  In many cases, the data doesn't make sense until we organize it into a graph.  There are several types of data, each using a specific type of graph.

1.Continuous Data goes on and on, usually over a period of time.  For this type of data, we use a line graph.

2. Discrete Data is data that occurs in clumps.  For this type of data, we use a bar graph.

3. Fractional or Percentage Data shows how much out of a whole.  For this type of data, we use a pie graph.

Variables are the things that change.  There are two types:

  1. Independent Variable is the one that you have no control over.  We often know what the independent variable will be before we run the experiment.  This usually goes on the x-axis.  (In graphing data over a period of time, time is the independent variable.)
  2. Dependent Variable changes as the independent variable changes.  We usually don't know what the dependent variable will be.  This usually goes on the y-axis.

For example, you might try to predict what your classmates will wear each day of the week.  You already know the days of the week, as these will always progress in the same order, so this is the independent variable.  You don't know what your classmates will wear, as it will change from day to day, so this is the dependent variable.

In an experiment, we often talk about control groups and experimental groups.
  - The control group is the group that you do not do any
    experimental procedure to.  You leave it as normal as possible,
    so you have something to compare to.
  - The experimental group is the group that you test in the
    experiment.  You will compare this one to the control group to
    see how your experiment worked.
For example, if I wanted to see how Chemical X affects a plant, I would set up two pots with plants in them.  One plant, the control, I would just water normally.  The other plant, I would water and give Chemical X to.  Then I could observe any differences between the two plants.