Formatting a testable hypothesis
What Is a Real Hypothesis?
A
hypothesis is a tentative statement that proposes a possible explanation to
some phenomenon or event. A useful hypothesis is a testable statement,
which may include a prediction. A hypothesis should not be confused with a
theory. Theories are general explanations based on a large amount of data. For
example, the theory of evolution applies to all living things and is based on
wide range of observations. However, there are many things about evolution that
are not fully understood such as gaps in the fossil record. Many hypotheses
have been proposed and tested.
When Are Hypotheses Used?
The key word is testable.
That is, you will perform a test of how two variables 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?
- 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.
All of these are
examples of hypotheses because they use the tentative word "may”. However,
their form is not particularly useful. Using the word “may” does not suggest
how you would go about providing supporting evidence for the hypothesis. If
these statements had not been written carefully, they may not have even been
hypotheses at all. For example, if we say "Trees will change color when it
gets cold." we are making a prediction. Or if we write, "Ultraviolet
light causes skin cancer." could be a conclusion. One way to prevent
making such easy mistakes is to formalize the form of the hypothesis.
Formalized Hypotheses example: 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.
If leaf color change is related
to temperature , then exposing plants to low temperatures will result
in changes in leaf color.
Notice that these
statements contain the words , if and then. They are necessary in
a formalized hypothesis. But not all if-then statements are hypotheses. For
example, "If I play the lottery, then I will get rich." This is a
simple prediction. In a formalized hypothesis, a tentative relationship is
stated. For example, if the frequency of winning is related to frequency
of buying lottery tickets. "Then" is followed by a prediction of what
will happen if you increase or decrease the frequency of buying lottery
tickets. If you always ask yourself that if one thing is related to another,
then you should be able to test it.
Formalized
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
The ultimate value of a
formalized hypothesis is it forces us to think about what results we should
look for in an experiment.
Notice there are two parts to a formalized hypothesis: the
“if” portion contains the testable proposed relationship and the “then” portion
is the prediction of expected results from an experiment. An acceptable hypothesis contains both
aspects, not just the prediction portion.
Investigation 1: Conducting a Biological
Experiment
Purpose: to learn how to use the scientific method by
conducting an experiment.
You have learned so far that
scientists use the "scientific method" in solving problems. Although
there is no set order to the sequence, a scientific investigation may include
some or all of the following activities; literature search, stating the
problem, writing a hypothesis, designing an experiment, collecting
data/observation, verification, graphing data, interpreting data, and forming a
conclusion.
For today’s experiment you will develop a
formalized hypothesis based upon the part II experiment of the lab exercise on
page 5 of the lab manual (including both testable relationship and prediction).
Each lab group will Set-up both experiments; pages 4 and 5 of the lab
manual. During the next week each lab
group will collect data in tables .
Once the data is collected your group will have to summarize the data
and represent the results using a table and figure.
Step 1: Introduction material before beginning an experiment.
Refer
to page 4 of your lab manual for a description of the experiment. Notice that
page 4 includes introductory information that explains the underlying hypothesis of spontaneous generation.
A. State the Problem (this is usually a general
question but often does not include a
proposed relationship)
What
is the general question addressed by Procedure 1?
(notice this is not a formalized hypothesis;
it does not contain any information to identify the independent or dependent
variable. This step is not included in
a formal lab report introduction section.)
B. Literature Search (this section is required
to explain the reason for a proposed
relationship [the hypothesis])
What background
information is required to explain your formalized hypothesis? For the formal
lab report you need to find appropriate cited sources to support your hypothesis.
___________________________________________________________________
___________________________________________________________________
C. Writing a Hypothesis
Procedure 1 page 4 of the lab manual
Read the procedure on page 4
of the lab manual to determine the independent and dependent variables. Write a formalized
hypothesis. Include the dependent and
independent variables.
Procedure 2 page 5 of the lab manual
Read procedure II on page 5
of the lab manual to determine the independent and dependent variables. Write a formalized
hypothesis. Include the dependent and
independent variables.
1. Are the independent and dependent variables
the same for both procedures?
2. Are the hypotheses for procedure 1 and
procedure II the same?
If not what relationship does
procedure II test?
Experimental
Design: Follow the instructions on
page 4 and 5 of your lab manual.
The following tables are meant
to aid in collecting the raw experimental data. Do not use these tables in the final lab report; follow the
example table in the handout on how to write a results section.
*Note this is not the final
table to use in your formal lab report.
Data/Observations
Table 1. Time – series data for your own group. Record the dependent variable each assigned
day.
Procedure 1: Dependent variable?_________________________
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surface sampled |
Day __ |
Day __ |
Day __ |
Day __ |
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Table 2. Time – series data for
your own group. Record the dependent
variable each assigned day. Each group must have a sediment score for each
treatment for four days; this data will be used to generate a time-series graph
for the lab report.
Procedure 2 Dependent
variable=__Sediment Score_
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Flask opening treatment |
Day __ |
Day __ |
Day __ |
Day __ |
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Interpretations and Conclusions
- Why should the results from each
group be combined with other class group data? before analyzing the
results for a lab report?
___________________________________________________________________ - What was the independent variable of
Procedure I?____________ Procedure
II? ______________________________ What was the dependent variable of
Procedure I?______________ Procedure II?_____________________________
- Why were five Petri dishes necessary
Procedure I ? What is the purpose of including the fifth Petri dish if the
lid was never removed?
___________________________________________________________________
___________________________________________________________________ 
Write
a conclusion for Procedure II that will support your group’s hypothesis
(Describe how the independent and dependent variable are related).
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
Check
the class standard flasks for the sediment scale:
During
next week’s lab each group will present their results and fill in a class data
table, see below. The class data table is the data that must be used for
the Chi-square test in your lab report.
Table
3. Bio 100 class data for Procedure II,
page 5 of the lab manual. The sediment
scores are based upon the score assigned to each flask on day 5. n= 6.
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Flask opening treatment |
Sediment
score on Day 5. |
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Group 1 |
Group 2 |
Group 3 |
Group 4 |
Group 5 |
Group 6 |
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No
Cotton plug |
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Cotton
plug |
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Cotton
plug w/ straight glass tube |
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Cotton
plug w/ curved glass tube |
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