In any industry, the ability to use observations and create a compelling hypothesis to solve a problem through research is very valuable. Scientists, data analysts and medical professionals should all learn how to write a hypothesis to guide their research. A good hypothesis is an important part of using research methods that lead to impactful research.
In this guide, we define a hypothesis and the elements that make up a complete hypothesis. We also cover a number of hypothesis examples and answer questions about making a hypothesis. By the time you finish reading this article, you will know how to write a hypothesis that is perfect for any research project or empirical research paper.
What is a hypothesis?
A hypothesis is a testable statement used in research, and researchers use the hypothesis to design an experiment that produces results that may or may not support the hypothesis. People constantly make causal hypotheses when solving problems. For example, if you assume that restarting your computer solves the problem you’re having with a program, then that statement is testable, because you can restart your computer and see if that fixes the problem.
What are the elements of a hypothesis?
- Explanation of the research question. A hypothesis is the research question rewritten as a testable statement. You must include the purpose of the study, the variables, the relationship between variables, and a testable prediction. Without a clear research question, you could be conducting endless, aimless investigations.
- Independent variable. The independent variable is the part of the experiment where you change something. If you’re wondering whether different types of motor oil change your car’s mileage, motor oil is the independent variable. This is usually based on an idea you have come up with to solve a problem.
- Dependent variable. The dependent variable is the part of the experiment where you measure the outcome and collect data. In the motor oil example above, the dependent variable is the car’s mileage, because that’s what you’re measuring.
- Predicted relationship between the independent and dependent variable. The goal of your hypothesis is to make an informed estimate of the influence of the independent variable on the dependent variable. You can assume that different types of motor oil have no effect on the mileage of a car, or that one type of motor oil increases the mileage of the car. This is also the declarative statement.
- testability. You must be able to test your hypothesis through experiments. A hypothesis like “Unicorns prefer cake to cookies” is untestable because there are no unicorns to experiment with.
Writing a Hypothesis: Beginning and End
To write a solid hypothesis, you need to understand the scientific method and basic format of a hypothesis. A strong, testable hypothesis turns random ideas into scientific experiments. A well-written hypothesis is usually a single sentence. Let’s see how to start and end a strong hypothesis.
How to start a hypothesis?
The beginning of your hypothesis introduces the variables. Remember that the independent variable is the thing you change in your experiment and the dependent variable is the thing you measure. In the example “Flowers watered with lemonade grow faster than flowers watered with regular water”, water and lemonade are the independent variables and the growth rate of flowers is the dependent variable.
Many people choose to structure hypotheses as an if-then statement. For example, “If you drink coffee before going to bed, it will take you longer to fall asleep.” If you’re having trouble with the hypothesis writing process, try starting with an if-then statement.
How to end a hypothesis?
In the second part of a simple hypothesis statement, you predict the relationship between the types of variables. Using our coffee example above, the second half of the sentence shows how we expect the amount of coffee to affect the time it takes to fall asleep.
As you write your prediction, remember to ask yourself, “Is this hypothesis testable?” You can predict that there will be no relationship between your variables, that the independent variable will have an effect on the dependent variable, or you can make a specific estimate of how the independent variable will affect the dependent variable. Bad hypotheses are not testable because there is no way to prove or disprove your original idea.
Writing a hypothesis: 5 more useful tips
Do preliminary research
To make a scientific hypothesis, you need to gain background knowledge on your topic by reading past studies, scientific experiments, and academic journals. You need to become a science student again. Be open-minded and research research that does and does not support your ideas. Learn about the experimental methods other people are using and look for any gaps in knowledge you could fill with your research question.
Define a research question
The first step in formulating a hypothesis is to brainstorm a research question. Use your writing skills to write a research question that is specific, clear, focused and manageable. Make sure you have the resources to run the experiment you need to answer the question.
Formulate a hypothesis
Use your new background knowledge to rewrite your research question as a testable statement. Don’t forget to include an independent variable, a dependent variable, and predict how they are related. Use an if-then statement if you’re having trouble.
Refine your hypothesis
The first version of a hypothesis is rarely perfect. You need to edit and proofread to find and fix errors. Make sure your hypothesis is testable and contains all relevant variables. Try having a colleague or advisor read your hypothesis and suggest changes.
Creating a null and alternative hypothesis
A null hypothesis always states that there is no relationship between variables while an alternative hypothesis states that there is some kind of relationship between variables. You must write both a null hypothesis and an alternative hypothesis for statistical analysis. An example of a null hypothesis from our coffee example is, “If you drink coffee before going to bed, it won’t affect how long it takes to fall asleep.”
Hypothesis Examples to help you write a hypothesis
The best way to learn to write a hypothesis is to read sample hypotheses. Below are some sample hypotheses.
Hypothesis Example 1: Smoking and Lung Cancer
A hypothesis examines the relationship between independent and dependent variables. Let’s say we’re interested in the relationship between smoking habits and lung cancer. Our independent variable is smoking habits and our dependent variable is lung cancer.
Next, we need to use our hypothesis to make a prediction about the relationship between smoking behavior and lung cancer. Based on background knowledge, we might suspect that daily smoking increases the risk of lung cancer. This is our alternative hypothesis. The null hypothesis requires that we predict that there is no relationship between the variables.
Our null hypothesis is: “Daily smoking does not affect the risk of lung cancer.” Our alternative hypothesis is, “Smoking daily increases the risk of lung cancer.” Both hypotheses have an independent and dependent variable, both are testable and both predict a relationship between the two variables.
Hypothesis Example 2: Vitamins and Hair Growth Rate
Let’s say you work for a company that distributes vitamins. You think vitamins E and K help hair growth, but there’s limited evidence on how these different vitamins affect hair growth. You decide to conduct a single experiment on the influence of vitamins on hair growth for scientific exploration.
You have a strong research question: “Does Vitamin E or Vitamin K Make Your Hair Grow Faster?” Now we need to turn that into an experimental hypothesis. Our independent variable is which vitamins to take and our dependent variable is the hair growth rate. This is a complex hypothesis because we are testing two vitamins, two independent variables.
The null hypothesis is, “Neither vitamin E nor vitamin K affect hair growth rate.” One possible alternative hypothesis is, “Both Vitamin E and K increase hair growth rate.” There are also a few other possible alternative hypotheses, depending on what you think the relationship is between vitamin E and hair growth versus vitamin K and hair growth.
How to use hypothesis examples to write your own hypotheses
The hypothesis examples we’ve discussed should give you a starting point for writing your own hypotheses. Use your research skills to develop a research question, then use our tips to rewrite it into a testable hypothesis with a simple prediction.
Frequently asked questions about writing a hypothesis
A hypothesis is a statement that describes a research question and predicts a relationship between variables. The same information can be asked as a question, but a true hypothesis is written as a statement. Hypotheses are often written as if-then statements.
A null hypothesis is a type of hypothesis that predicts that there is no relationship between your variables. For example, if your research question is, “Is it important to integrate mental health education in schools?” Your Null Hypothesis is: “Implementation of Mental Health Education in Schools” will not influence students.
An alternative hypothesis means that you expect a relationship between variables. Let’s use the research question, “Is it important to integrate mental health education in schools?” An alternative hypothesis for that would be “Implementing mental health education in school curricula” shall affect students.”
A good hypothesis is a simple statement of a research question that is testable and should contain a dependent variable, an independent variable, and a prediction of the relationship between the two variables. There are also specific types of hypotheses, such as a directional hypothesis, a non-directional hypothesis, or an associative hypothesis.
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