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?

  1. Chocolate may cause pimples.
  2. Salt in soil may affect plant growth.
  3. Plant growth may be affected by the color of the light.
  4. Bacterial growth may be affected by temperature.
  5. Ultra violet light may cause skin cancer.
  6. 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.


Table 1.  Time – series data for your own group.  Record the dependent variable each assigned day.

Procedure 1:  Dependent variable?_________________________

surface sampled

Day ­__

Day ­__

Day ­__

Day ­__



























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_

Flask opening treatment


Day ­__

Day ­__

Day ­__

Day ­__




























Interpretations and Conclusions

  1. Why should the results from each group be combined with other class group data? before analyzing the results for a lab report?

  2. What was the independent variable of Procedure I?____________  Procedure II? ______________________________ What was the dependent variable of Procedure I?______________ Procedure II?_____________________________
  3. Why were five Petri dishes necessary Procedure I ? What is the purpose of including the fifth Petri dish if the lid was never removed?


  4. 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. 


Flask opening treatment


Sediment score on Day 5.


Group 1

Group 2

Group 3

Group 4

Group 5

Group 6


No Cotton plug








Cotton plug








Cotton plug w/

 straight glass tube








Cotton plug w/

 curved glass tube