How To Write A Hypothesis Statement Science

By Science Buddies on February 23, 2010 9:23 AM


"If _____[I do this] _____, then _____[this]_____ will happen."


Sound familiar? It should. This formulaic approach to making a statement about what you "think" will happen is the basis of most science fair projects and much scientific exploration.

Step by Step
You can see from the basic outline of the Scientific Method below that writing your hypothesis comes early in the process:
  1. Ask a Question
  2. Do Background Research
  3. Construct a Hypothesis
  4. Test Your Hypothesis by Doing an Experiment
  5. Analyze Your Data and Draw a Conclusion
  6. Communicate Your Results

Following the scientific method, we come up with a question that we want to answer, we do some initial research, and then before we set out to answer the question by performing an experiment and observing what happens, we first clearly identify what we "think" will happen.

We make an "educated guess."

We write a hypothesis.

We set out to prove or disprove the hypothesis.

What you "think" will happen, of course, should be based on your preliminary research and your understanding of the science and scientific principles involved in your proposed experiment or study. In other words, you don't simply "guess." You're not taking a shot in the dark. You're not pulling your statement out of thin air. Instead, you make an "educated guess" based on what you already know and what you have already learned from your research.

If you keep in mind the format of a well-constructed hypothesis, you should find that writing your hypothesis is not difficult to do. You'll also find that in order to write a solid hypothesis, you need to understand what your variables are for your project. It's all connected!

If I never water my plant, it will dry out and die.

That seems like an obvious statement, right? The above hypothesis is too simplistic for most middle- to upper-grade science projects, however. As you work on deciding what question you will explore, you should be looking for something for which the answer is not already obvious or already known (to you). When you write your hypothesis, it should be based on your "educated guess" not on known data. Similarly, the hypothesis should be written before you begin your experimental procedures—not after the fact.



Hypotheses Tips

Our staff scientists offer the following tips for thinking about and writing good hypotheses.

  • The question comes first. Before you make a hypothesis, you have to clearly identify the question you are interested in studying.
  • A hypothesis is a statement, not a question. Your hypothesis is not the scientific question in your project. The hypothesis is an educated, testable prediction about what will happen.
  • Make it clear. A good hypothesis is written in clear and simple language. Reading your hypothesis should tell a teacher or judge exactly what you thought was going to happen when you started your project.
  • 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. (For more information about identifying variables, see: Variables in Your Science Fair Project.)
  • 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.

    To create a "testable" hypothesis make sure you have done all of these things:

    • Thought about what experiments you will need to carry out to do the test.
    • Identified the variables in the project.
    • Included the independent and dependent variables in the hypothesis statement. (This helps ensure that your statement is specific enough.
  • Do your research. You may find many studies similar to yours have already been conducted. What you learn from available research and data can help you shape your project and hypothesis.
  • Don't bite off more than you can chew! Answering some scientific questions can involve more than one experiment, each with its own hypothesis. Make sure your hypothesis is a specific statement relating to a single experiment.


Putting it in Action

To help demonstrate the above principles and techniques for developing and writing solid, specific, and testable hypotheses, Sandra and Kristin, two of our staff scientists, offer the following good and bad examples.

Good HypothesisPoor Hypothesis
When there is less oxygen in the water, rainbow trout suffer more lice.

Kristin says: "This hypothesis is good because it is testable, simple, written as a statement, and establishes the participants (trout), variables (oxygen in water, and numbers of lice), and predicts effect (as oxygen levels go down, the numbers of lice go up)."

Our universe is surrounded by another, larger universe, with which we can have absolutely no contact.

Kristin says: "This statement may or may not be true, but it is not a scientific hypothesis. By its very nature, it is not testable. There are no observations that a scientist can make to tell whether or not the hypothesis is correct. This statement is speculation, not a hypothesis."

Aphid-infected plants that are exposed to ladybugs will have fewer aphids after a week than aphid-infected plants which are left untreated.

Sandra says: "This hypothesis gives a clear indication of what is to be tested (the ability of ladybugs to curb an aphid infestation), is a manageable size for a single experiment, mentions the independent variable (ladybugs) and the dependent variable (number of aphids), and predicts the effect (exposure to ladybugs reduces the number of aphids)."

Ladybugs are a good natural pesticide for treating aphid infected plants.

Sandra says: "This statement is not 'bite size.' Whether or not something is a 'good natural pesticide' is too vague for a science fair project. There is no clear indication of what will be measured to evaluate the prediction."



Hypotheses in History

Throughout history, scientists have posed hypotheses and then set out to prove or disprove them. Staff Scientist Dave reminds that scientific experiments become a dialogue between and among scientists and that hypotheses are rarely (if ever) "eternal." In other words, even a hypothesis that is proven true may be displaced by the next set of research on a similar topic, whether that research appears a month or a hundred years later.

A look at the work of Sir Isaac Newton and Albert Einstein, more than 100 years apart, shows good hypothesis-writing in action.

As Dave explains, "A hypothesis is a possible explanation for something that is observed in nature. For example, it is a common observation that objects that are thrown into the air fall toward the earth. Sir Isaac Newton (1643-1727) put forth a hypothesis to explain this observation, which might be stated as 'objects with mass attract each other through a gravitational field.'"

Newton's hypothesis demonstrates the techniques for writing a good hypothesis: It is testable. It is simple. It is universal. It allows for predictions that will occur in new circumstances. It builds upon previously accumulated knowledge (e.g., Newton's work explained the observed orbits of the planets).

"As it turns out, despite its incredible explanatory power, Newton's hypothesis was wrong," says Dave. "Albert Einstein (1879-1955) provided a hypothesis that is closer to the truth, which can be stated as 'objects with mass cause space to bend.' This hypothesis discards the idea of a gravitational field and introduces the concept of space as bendable. Like Newton's hypothesis, the one offered by Einstein has all of the characteristics of a good hypothesis."

"Like all scientific ideas and explanations," says Dave, "hypotheses are all partial and temporary, lasting just until a better one comes along."

That's good news for scientists of all ages. There are always questions to answer and educated guesses to make!



If your science fair is over, leave a comment here to let us know what your hypothesis was for your project.


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The American Heritage Dictionary defines a hypothesis as, "a tentative explanation for an observation, phenomenon, or scientific problem that can be tested by further investigation." This means a hypothesis is the stepping stone to a soon-to-be proven theory. For a hypothesis to be considered a scientific hypothesis, it must be proven through the scientific method. Like anything else in life, there are many paths to take to get to the same ending. Let's take a look at the different types of hypotheses that can be employed when seeking to prove a new theory.

Types of Hypothesis

First, we must take a moment to define independent and dependent variables. Simply put, an independent variable is the cause and the dependent variable is the effect. The independent variable can be changed whereas the dependent variable is what you're watching for change. For example: How does the amount of makeup one applies affect how clear their skin is? Here, the independent variable is the makeup and the dependent variable is the skin.

The six most common forms of hypotheses are:

  • Simple Hypothesis
  • Complex Hypothesis
  • Empirical Hypothesis
  • Null Hypothesis (Denoted by "HO")
  • Alternative Hypothesis (Denoted by "H1")
  • Logical Hypothesis
  • Statistical Hypothesis

A simple hypothesis is a prediction of the relationship between two variables: the independent variable and the dependent variable.

  • Drinking sugary drinks daily leads to obesity. 

A complex hypothesis examines the relationship between two or more independent variables and two or more dependent variables. 

  • Overweight adults who 1) value longevity and 2) seek happiness are more likely than other adults to 1) lose their excess weight and 2) feel a more regular sense of joy. 

A null hypothesis (H0) exists when a researcher believes there is no relationship between the two variables, or there is a lack of information to state a scientific hypothesis. This is something to attempt to disprove or discredit. 

  • There is no significant change in my health during the times when I drink green tea only or root beer only.

This is where the alternative hypothesis (H1) enters the scene. In an attempt to disprove a null hypothesis, researchers will seek to discover an alternative hypothesis.

  • My health improves during the times when I drink green tea only, as opposed to root beer only.

A logical hypothesis is a proposed explanation possessing limited evidence. Generally, you want to turn a logical hypothesis into an empirical hypothesis, putting your theories or postulations to the test. 

  • Cacti experience more successful growth rates than tulips on Mars. (Until we're able to test plant growth in Mars' ground for an extended period of time, the evidence for this claim will be limited and the hypothesis will only remain logical.)

An empirical hypothesis, or working hypothesis, comes to life when a theory is being put to the test, using observation and experiment. It's no longer just an idea or notion. It's actually going through some trial and error, and perhaps changing around those independent variables.

  • Roses watered with liquid Vitamin B grow faster than roses watered with liquid Vitamin E. (Here, trial and error is leading to a series of findings.)

A statistical hypothesis is an examination of a portion of a population. 

  • If you wanted to conduct a study on the life expectancy of Savannians, you would want to examine every single resident of Savannah. This is not practical. Therefore, you would conduct your research using a statistical hypothesis, or a sample of the Savannian population. 

Parameters of a Good Hypothesis

In order for a hypothesis to be sound, hold tight to these tips:

Ask yourself questions.

  • Brainstorm. Define the independent and dependent variables very specifically, and don't take on more than you can handle. Keep yourself laser-focused on one specific cause-and-effect theory.

Be logical and use precise language.

  • Keep your language clean and simple. State your hypothesis as concisely, and to the point, as possible. A hypothesis is usually written in a form where it proposes that, if something is done, then something else will occur. Usually, you don't want to state a hypothesis as a question. You believe in something, and you're seeking to prove it. For example: If I raise the temperature of a cup of water, then the amount of sugar that can be dissolved in it will be increased.

Make sure your hypothesis is testable with research and experimentation.

  • Any hypothesis will need proof. Your audience will have to see evidence and reason to believe your statement. For example, I may want to drink root beer all day, not green tea. If you're going to make me change my ways, I need some sound reasoning and experimental proof - perhaps case studies of others who lost weight, cleared up their skin, and had a marked improvement in their immunity by drinking green tea.

State Your Case

Scientists can really change the world with their hypotheses and findings. In an effort to improve the world we live in, all it takes is an initial hypothesis that is well-stated, founded in truth, and can withstand extensive research and experimentation. Seek out your independent and dependent variables and go on out here and make this world a better place. Good luck!

Do you have a good example to share? Add your example here.

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Examples of Hypothesis

By YourDictionary

The American Heritage Dictionary defines a hypothesis as, "a tentative explanation for an observation, phenomenon, or scientific problem that can be tested by further investigation." This means a hypothesis is the stepping stone to a soon-to-be proven theory. For a hypothesis to be considered a scientific hypothesis, it must be proven through the scientific method. Like anything else in life, there are many paths to take to get to the same ending. Let's take a look at the different types of hypotheses that can be employed when seeking to prove a new theory.

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