Name_______________________________________________Date________________Period______
Writing Hypotheses the VCR Way
All well designed experiments include two groups, a control group and an experimental group. The
experimental group differs from the control group in one way or by one factor only. This difference is
called the variable and it is the factor the experiment is designed to test. The control group is used as
our point of comparison. If the results from the two groups differ, we can assume that this difference
was caused by the action of the variable. But how do we predict what will happen? By formulating our
hypothesis.
In science, a hypothesis is a tentative answer to a well-framed question. It can be an educated guess
based on 1) prior knowledge or 2) recently conducted research. In AP Biology, all students are expected
to be able to write relevant hypotheses before they begin the laboratory exercises. You should also
expect to be asked to design your own experiments and be able to write an applicable hypothesis.
One way of gaining confidence in doing this is to apply the VCR method. These letters will guide you
through the thinking process and help you construct a hypothesis framed in the correct format. These
letters stand for:
V: what is the variable we will be testing?
C: how will this variable change?
R: what will be the expected response to this change?
After you answer the preceding questions, you can arrange that information in the following order:
If (V – describe the variable), then when (C – describe how it will change), (R – describe the response).
By applying this method to the following scenario, you will learn how to construct hypotheses in the
correct format.
Mary wants to investigate factors that affect plant growth. She knows that plants need lots of bright
light in order to grow well. She will grow some plants in front of a window and other plants behind a
screen.
V : what is the variable she will test? Light
C : how will this variable change? She will reduce the amount of light that some plants receive.
R : what will be the expected response? She expects the plant that gets less light will grow less.
Hypothesis:
If (V: describe the variable), then when (C: describe how it will change), (R: describe the response).
If light affects the rate of growth in plants, then when plants are exposed to reduced light levels, we
should see less growth.
Pete is investigating the effect of different pet foods on the condition and appearance of his dog’s coat.
He knows that fur is made of protein. He believes that pet foods that contain more protein will produce
a shinier coat on his dog. He buys several different varieties of dog food to feed to his dog.
V: what is the variable he will test?_____________________________________________________
C: how will this variable change?_______________________________________________________
R: what will be the expected response?__________________________________________________
Hypothesis:
Paul just got his driver’s license and now owns his own used car. Since he doesn’t have a lot of money,
he is interested in learning which grade of gasoline will give him the best mileage. He recalls reading in a
magazine that the higher the octane level of the gas, the better it is for your car. He decides to put this
idea to the test by filling his gas tank with different grades of gas and recording his mileage.
V: what is the variable he will test?_____________________________________________________
C: how will this variable change?_______________________________________________________
R: what will be the expected response?__________________________________________________
Hypothesis:
Jack likes to listen to music while he studies but his mother is always telling him to pull out his ear buds
and get to work! He wants to know if listening to music really interferes with his ability to concentrate,
as his mother claims. He decides to conduct an experiment with his friends since they are all studying
for an AP Biology quiz. He thinks background music causes him to relax, thereby improving his
concentration. He asks his friends to help him conduct a simple experiment.
V: what is the variable he will test?_____________________________________________________
C: how will this variable change?_______________________________________________________
R: what will be the expected response?__________________________________________________
Hypothesis:
Now, briefly outline your own experiment and write an appropriate and relevant hypothesis using the
above format.