Name: _____________________________ Period: ______ Date: _______________ Score: _________
Writing an “If…Then…” Hypothesis
Purpose: To learn how to write testable hypotheses.
When using the “scientific method” to conduct an experiment, you do not always know the results of the
lab; however, you can independently find a verifiable answer. In real experiments, real hypotheses should
be written before the actual experiment.
What Is a Real Hypothesis?
A hypothesis is a statement that proposes a possible explanation to some phenomenon or event. A useful
hypothesis is a testable statement which may include a prediction. It predicts the relation between two
variables.
1) What is a ‘variable’ in Science?
2) What are the three types of variables?
A hypothesis statement must be testable. That is, you will perform a test of how two variables
(independent and dependent) might be related. This is when you are doing a real experiment. You are
testing variables.
Usually, a hypothesis is based on some previous observation such as noticing that in November many trees
undergo color changes in their leaves and the average daily temperatures are dropping. Are these two
events connected? How?
Any laboratory procedure you follow without a hypothesis is really not an experiment. It is just an
exercise or demonstration of what is already known.
How Are Hypotheses Written?
All of these are examples of hypotheses because they use the word "may." However, their form is not
particularly useful. Using the word “may” does not suggest how you would go about proving or testing it.
Good hypotheses contain two variables. One is "independent" and the other is "dependent." The
independent variable is the one you, the "scientist" control and the dependent variable is the one that you
observe and/or measure the results. Use quantitative indicators such as ‘increasing/decreasing’ before the
independent variable and state how the dependent behavior will respond. In the hypothesis about skin
cancer below, the independent variable is single underlined and the dependent variable is double
underlined.
Example of a Testable Hypothesis: If skin cancer is related to ultraviolet light , then people
with a high exposure to uv light will have a higher frequency of skin cancer.
Notice that these statements contain the words “if” and “then”. They are necessary in a good hypothesis.
But not all if-then statements are hypotheses. For example, "If I play the lottery, then I will get rich."
The previous statement - If I play the lottery, then I will get rich - is a simple prediction and not a
hypothesis.
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Why?______________________________________________________________________
Let’s Practice:
A) In the table below, rewrite the 6 hypotheses using the if –then style shown. Single underline the
independent variable and double underline the dependent variable in the hypothesis.
1.
2.
3.
4.
5.
6.
Chocolate may cause pimples.
Acid in soil may affect plant growth.
Watching TV leads to bad grades.
Bacterial growth may be affected by temperature.
Ultra violet light may cause skin cancer.
Temperature may cause leaves to change color.
1.
2.
3.
4.
5.
6.
B) Write a hypothesis statement for each of these questions - Going from a question to a hypothesis:
1) Does temperature affect the performance of a track athlete in a 100 m race?
2) Does cell phone usage cause car accidents?
3) Does spending more time on Homework increase your chances of getting an ‘A’ in Biology?
C) Now, for each of these hypotheses, think about what your controlled variables need to be in the
experiment? List 2 controlled variables for TWO of your hypotheses.