Most science investigations require a controlled experiment. A controlled experiment is an
experiment in which only one variable is tested at a time.
Investigations will often refer to both an independent and dependent variable. Independent and dependent
variables are related to one another.
The independent (or manipulated) variable is the variable that you,
the experimenter, change or manipulate intentionally.
Dependent (or responding) variable is the variable that changes when the independent variable changes. The
dependent variable depends on the outcome of the independent variable.
Here are some simplified examples:
With each of these experiments, it is very important to control the experiment.
| Question|| Independent Variable||Dependent Variable |
| Does water help plants grow best?|| Type of liquid (water, vinegar, etc)|| Height of plant (in cm)|
|What kind of teaching helps kids learn best? || Type of instruction (reading, lecture, video, lab)|| Score on test|
| Does the form of sugar affect how quickly is dissolves?|| Form of sugar (granulated, powdered, cube)|| Time to dissolve (in seconds)|
Question 1: You ONLY want to test the TYPE of liquid. Imagine you watered one plant with water every day and another plant with vinegar every other day. If you found the plant given vinegar grew less tall, you wouldn't know if it is because of the type of liquid or the frequency of which you watered the plant. There are TOO MANY VARIABLES. Kids will relate to this being a "fair" comparison or not. In this investigation, the following variables must be kept the same between the two plants: the type of plant, size of container, amount of sunlight each day, temperature, amount of liquid, how frequently the plant is watered… etc. These variables that are kept the same are called controlled variables.
Of course, we cannot control everything in an experiment. We may have the same types of plant, but one seed was not as robust. Perhaps when we planted the seed, one seed was slightly deeper in the pot than the other. These types of control mishaps constitute "experimental error."
Read more about variables and controls at:
When creating a graph, knowing your independent and dependent variables can help you quickly set up a graph. In general, the independent variable is drawn on the X axis and the dependent variable is drawn on the Y axis.
You can download Graph Hints (doc) to modify and share with students.
More resources about graphs: