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.
Write answers next to each question. Answers were discussed in class.
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 the examples on the next page 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.

Why?______________________________________________________________________
Let’s Practice:
A) In the table below, rewrite the 6 hypotheses using the if –then style shown.
B) Single underline the independent variable and double underline the dependent variable in the
hypothesis YOU WRITE in the table.
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.
Rewrite one hypothesis here: ________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
Controlled Variable 1:
Controlled Variable 2:
Rewrite one hypothesis here: ________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
Controlled Variable 1:
Controlled Variable 2:
Identifying Scientific Variables
Read through each of the “experiments” conducted by Bart Simpson and his TV gang and answer
the questions in the space provided. You do not need to use complete sentences.
Smithers made a new special drink
called “WORKEZ.” He thinks that this
special juice will increase the speed of
his office workers. He creates two
groups (A and B) of 50 workers each
and assigns each group the same task (in
this case, they’re supposed to staple a
set of papers). Group A is given the special juice to
drink while they work. Group B is not given the special
juice. After an hour, Smithers counts how many stacks of
papers each group has made.
Identify the:
Result: Group A made 1,587 stacks, Group B made
2,113 stacks.
5. What should Smithers’ conclusion be?
1. Control Group 2. Independent Variable –
3. Dependent Variable –
4. Write Smithers hypothesis (use “If…then”):
6. How could this experiment be improved?
Homer notices that his shower is
covered in a strange green slime. His
friend Barney tells him that coconut
juice will get rid of the green slime.
Homer decides to check this out by
spraying half of the shower with
coconut juice. He sprays the other half
of the shower with water.
Result: After 3 days of “treatment” there is no change in
the appearance of the green slime on either side of the
shower.
7. What was the initial observation?
Identify the8. Control Group –
9. Independent Variable –
10. Dependent Variable –
11. Write Homer’s hypothesis:
12. What should Homer’s conclusion be?
Bart believes that mice exposed to
microwaves will become extra
strong (maybe he’s been reading too
much Radioactive Man!). He decides
to perform this experiment by
placing 10 mice in a microwave for
10 seconds (don’t try this at home!).
He compared these 10 mice to another 10 mice that were
not put in the microwave. He tested the strength of the 2
groups of mice by placing a wood piece blocking its
food.
Result: Bart found that 8 out of 10 of the microwaved
mice were able to push the block away. 7 out of 10 of the
non-microwaved mice were also able to push the wood
block away.
Identify the –
13. Control Group –
14. Independent Variable –
15. Dependent Variable –
16. Write Bart’s hypothesis (“If…then.”):
17. What should Bart’s conclusion be?
18. How could Bart’s experiment be improved?
Krusty saw an advertisement that a
certain itching powder
“SCRATCHOMATIC” – was the
newest best thing on the market, it
even claims to cause 50% longer
lasting itches. Interested in this
product, he buys SCRATCHOMATIC and compares it to
another product “ITCHKING”. One test subject (A) is
sprinkled with ITCHKING itching powder, and another
test subject (B) was sprinkled with SCRATCHOMATIC
itching powder.
Identify the 19. Control Group –
Result: Subject A reported having itches for 30 minutes.
Subject B reported to have itches for minutes.
23. Explain whether the data supports the
advertisement’s claims about its product –
SCRATCHOMATIC.
Lisa is working on a science project. Her
task is to answer the question: “Does
Rogooti (which is a commercial hair
product) affect the speed of hair growth?”
Her family is willing to volunteer for the
experiment.
20. Independent Variable –
21. Dependent Variable –
22. Write Krusty’s hypothesis (“If…then.”):
24. Identify the control group, and the independent
and dependent variables in your description. Write
the hypothesis. Describe how the experiment will
be performed. (Can write below…use binder paper
if necessary).