What is a Hypothesis?
How does a
hypothesis begin?
What do you do with
it?
How do you make
one?
Making a hypothesis is a
step in the Scientific
Method
1.
2.
3.
4.
5.
6.
7.
The 7 basic steps of the scientific method:
Asking a question
Completing research
Making a hypothesis
Planning an investigation
Recording and analyzing data
Explaining the data
Communicating the results
How does a hypothesis
begin?
Scientists make lots of observations. This leads them
to form scientific questions about what they have
observed. Each scientist creates an explanation – or
hypothesis – that he or she thinks will answer the
question.
A scientist bases his/her hypothesis both on what he or
she has observed, and on what he or she already
knows to be true.
A hypotheses is not just a
prediction!
• In science a prediction is an educated guess about the
expected outcome of a specific test. In science a
hypothesis goes further.
• A hypothesis includes a possible explanation about
why the expected outcome of a test will occur
What do you do with a
hypothesis?
The hypothesis that a scientist creates leads him or her
to make a prediction that can be tested next in an
investigation.
• It does not matter if your experiment has
been done a thousand times before!
•
What matters is that you don't know the
results and that you can independently
find a verifiable answer.
What does verifiable mean?
It means capable of being tested
(verified or falsified)
How do you write a
hypothesis?
A good hypothesis includes two parts:
1. a prediction about the outcome of a scientific
investigation
----and----
2. an explanation for why those results will occur
Prediction vs. Hypothesis
Usually, a hypothesis is based on some previous
observation
Example Prediction:
If it gets cold outside then leaves will change colors.
Are these two events connected? How?
Example Hypothesis:
If it gets cold outside then the leaves will change color
because leaf color change is related to temperature.
How do you write a
hypothesis?
•
•
•
•
•
•
Chocolate may cause pimples.
Salt in soil may affect plant growth.
Plant growth may be affected by the color of the light.
Bacterial growth may be affected by temperature.
Ultra violet light may cause skin cancer.
Temperature may cause leaves to change color.
Do you think that these statements
make good hypotheses?
Why or why not?
How do you write a
hypothesis?
The word “may” does not suggest how we would prove these
statements
•
•
•
•
•
•
Chocolate may cause pimples.
Salt in soil may affect plant growth.
Plant growth may be affected by the color of the light.
Bacterial growth may be affected by temperature.
Ultra violet light may cause skin cancer.
Temperature may cause leaves to change color.
How do you write a
hypothesis?
A hypothesis is worded as a prediction about what will
happen if you change something and is worded like
this:
If … then… because…
Example: If students eat a lot of candy then they will get
more cavities because sugar on teeth causes
cavities.
http://iqa.evergreenps.org/science/games/
elephant.mpeg
Example question
Lets say you notice that the tomato plant closest to the
fence in your neighbor’s yard is much taller than any of
the other plants in her garden bed. You also notice
that the neighbor turns on her sprinkler system every
day, and that some of this water reaches only her big
plant.
You create a question:
Does daily watering from a sprinkler make a tomato plant
grow faster than other tomato plants?
Example hypothesis
Now you can create a hypothesis to address your
question:
“If tomato plants in a garden are watered daily then
they will grow faster because tomato plants grow
more when they get more water.”
Notice how the hypothesis makes a prediction that can
be tested
If….then….because….
After the word “If ”… explain what will change in the
investigation
After the word “then ” …write what you predict will
happen as a result of that change
After the word “because” …explain why you think the
result will happen
Testing a Hypothesis
The hypothesis must be worded so that it can be tested in
your experiment.
• Do this by expressing the hypothesis using an
independent variable (the variable you change during your
experiment) and a dependent variable (the variable you
observe changes in). The dependent variable depends on
• In
fact, many
hypotheses
arevariable).
changes
in the
independent
stated exactly like this:
" If a particular independent
variable is changed, then there is
a change in a certain dependent
variable, because of why you
think the result will happen “
Variables in Hypotheses
If… then… because
• If people are exposed to high amounts of ultraviolet light,
then they will have a higher frequency of skin cancer
because ultraviolet light causes skin cancer
• If leaves are exposed to low temperatures, then the leaves
will change color because the plant stops making
chlorophyll
DEPENDENT
VARIABLE
The variable that you observe
and measure the results
INDEPEND
ENT
VARIABLE
The variable that
If….then….because….
Practice
Original:
Ultra violet light may cause skin cancer.
• If… then…because
• If people are exposed to high amounts of ultraviolet light,
then they will have a higher frequency of skin cancer
because ultraviolet light causes skin cancer
Original:
Temperature may cause leaves to change color.
• If… then…because
• If leaves are exposed to low temperatures, then the leaves
will change color because the plant stops making
chlorophyll
Your Turn to Practice
Rewrite the following hypothesis as an If…
then…because statement.
• What is the dependent variable?
• What is the independent variable?
Chocolate may cause pimples.
Rewritten Hypothesis:
dependent variable:
independent variable:
Did your Hypothesis look
something like this?
Chocolate may cause pimples.
Rewritten hypothesis:
If I eat chocolate, then I will get pimples because
chocolate causes my skin to produce excess oil
which clogs the pores of my skin
Your Turn to Practice
Rewrite the following hypothesis as an If…
then…because statement.
• What is the dependent variable?
• What is the independent variable?
Salt in soil may affect plant growth.
Rewritten Hypothesis:
dependent variable:
independent variable:
Did your Hypothesis look
something like this?
Salt in soil may affect plant growth.
Rewritten hypothesis:
If salt is added to the soil, then the growth of the
plant will be affected because salt prevents the plant
from absorbing the water
Your Turn to Practice
Rewrite the following hypothesis as an If…
then…because statement.
• What is the dependent variable?
• What is the independent variable?
Plant growth may be affected by the color of the light.
Rewritten Hypothesis:
dependent variable:
independent variable:
Did your Hypothesis look
something like this?
Plant growth may be affected by the color of the light.
Rewritten hypothesis:
If the color of light is changed, then plant growth will
be affected because plants prefer different colors of
light!
Your Turn to Practice
Rewrite the following hypothesis as an If…
then…because statement.
• What is the dependent variable?
• What is the independent variable?
Bacterial growth may be affected by temperature.
Rewritten Hypothesis:
dependent variable:
independent variable:
Did your Hypothesis look
something like this?
Bacterial growth may be affected by temperature.
Rewritten hypothesis:
If the temperature is increased, then bacteria will
grow faster because those little buggers like it hot!
Summary – Hypothesis Writing
Tips
1. The question comes first. Before you make a hypothesis, you have to
clearly identify the question you are interested in studying.
2. A hypothesis is a statement, not a question. Your hypothesis is not the
scientific question. The hypothesis is an educated, testable prediction about
what will happen.
3. Make it clear. A good hypothesis is written in clear and simple language.
Reading your hypothesis should tell someone exactly what you thought
was going to happen when you started your experiment.
4. Keep the variables in mind. A good hypothesis defines the variables in
easy-to-measure terms, like who the participants are, what changes during
the testing, and what the effect of the changes will be.
5. Make sure your hypothesis is "testable." To prove or disprove your
hypothesis, you need to be able to do an experiment and take
measurements or make observations to see how two things (your
variables) are related. You should also be able to repeat your experiment
over and over again, if necessary.
6. Do your research. You may find many studies similar to yours have