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How to write a hypothesis

A hypothesis is a statement that introduces a research question and proposes an expected result. It is an integral part of the scientific method that forms the basis of scientific experiments. Therefore, you need to be careful and thorough when building your hypothesis. A minor flaw in the construction of your hypothesis could have an adverse effect on your experiment.

Essential Characteristics of a Good Hypothesis

As a research hypothesis is a specific, testable prediction about what you expect to happen in a study, you may consider drawing hypothesis from previously published research based on the theory.

A good research hypothesis involves more efforts than just a guess. In particular, your hypothesis may begin with a question which could be further explored through background research.

To help you formulate a promising research hypothesis, you should ask yourself the following questions:

  1. Is the language clear and focused?
  2. What is the relationship between your hypothesis and your research topic?
  3. Is your hypothesis testable? If yes, then how?
  4. What are the possible explanations that you might want to explore?
  5. Does your hypothesis include both an independent and dependent variable?
  6. Can you manipulate your variables without hampering the ethical standards?

The questions listed above can be used as a checklist to make sure your hypothesis is based on a solid foundation. Furthermore, it can help you identify weaknesses in your hypothesis and revise it if necessary.

Types of Research Hypothesis

Research hypothesis can be classified into seven categories as stated below:

1. Simple Hypothesis

It predicts the relationship between a single dependent variable and a single independent variable.

2. Complex Hypothesis

It predicts the relationship between two or more independent and dependent variables.

3. Directional Hypothesis

It specifies the expected direction to be followed to determine the relationship between variables, and is derived from theory. Furthermore, it implies researcher’s intellectual commitment to a particular outcome.

4. Non-directional Hypothesis

It does not predict the exact direction or nature of the relationship between the two variables. Non-directional hypothesis is used when there is no theory involved or when findings contradict previous research.

5. Associative and Causal Hypothesis

Associative hypothesis defines interdependency between variables. A change in one variable results in the change of the other variable. On the other hand, causal hypothesis proposes an effect on the dependent due to manipulation of the independent variable.

6. Null Hypothesis

It states a negative statement to support the researcher’s findings that there is no relationship between two variables.

7. Alternative Hypothesis

It states that there is a relationship between the two variables of the study and that the results are significant to the research topic.

How to Formulate an Effective Research Hypothesis

A testable hypothesis is not a simple statement. It is rather an intricate statement that needs to offer a clear introduction to a scientific experiment, its intentions, and the possible outcomes. However, there are some important things to consider when building a compelling hypothesis.

  1. State the problem that you are trying to solve.
    • Make sure that the hypothesis clearly defines the topic and the focus of the experiment.
  2. Try to write the hypothesis as an if-then statement.
    • Follow this template: If a specific action is taken, then a certain outcome is expected.
  3. Define the variables

Independent variables are the ones which are manipulated, controlled, or changed. Independent variables are isolated from other factors of the study.

Dependent variables, as name suggests are dependent on other factors of the study. They are influenced by the change in independent variable.

Examples of Independent and Dependent Variables in a Hypothesis:

Example 1
The greater number of coal plants in a region (independent variable) increases water pollution (dependent variable).

If you change the independent variable (building more coal factories), it will change the dependent variable (amount of water pollution).

Example 2
What is the effect of diet or regular soda (independent variable) on blood sugar levels (dependent variable)?

If you change the independent variable (the type of soda you consume), it will change the dependent variable (blood sugar levels)

You should not ignore the importance of the above steps. The validity of your experiment and its results rely on a robust testable hypothesis. Developing a strong testable hypothesis has few advantages, it compels us to think intensely and specifically about the outcomes of a study. Consequently, it enables us to understand the implication of the question and the different variables involved in the study. Furthermore, it helps us to make precise predictions based on prior research. Hence, forming a hypothesis would be of great value to the research. Here are some good examples of testable hypotheses.

More importantly, you need to build a robust testable research hypothesis for your scientific experiments. A testable hypothesis is a hypothesis that can be proved or disproved as a result of experimentation.

Importance of a Testable Hypothesis

To devise and perform an experiment using scientific method, you need to make sure that your hypothesis is testable. To be considered testable, some essential criteria must be met:

  1. There must be a possibility to prove that the hypothesis is true.
  2. There must be a possibility to prove that the hypothesis is false.
  3. The results of the hypothesis must be reproducible.

Without these criteria, the hypothesis and the results will be vague. As a result, the experiment will not prove or disprove anything significant.

What are your experiences with building hypotheses for scientific experiments? What challenges did you face? How did you overcome these challenges? Please share your thoughts with us in the comments section. You can also visit our Q&A forum for frequently asked questions related to different aspects of research writing and publishing answered by our team that comprises subject-matter experts, eminent researchers, and publication experts.

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Published on April 23, 2019 by Shona McCombes. Revised on January 5, 2022.

A hypothesis is a statement that can be tested by scientific research. If you want to test a relationship between two or more things, you need to write hypotheses before you start your experiment or data collection.

Example hypothesis

Daily apple consumption leads to fewer doctor’s visits.

Table of contents

  1. What is a hypothesis?
  2. Developing a hypothesis
  3. Hypothesis examples
  4. Frequently asked questions

What is a hypothesis?

A hypothesis states your predictions about what your research will find. It is a tentative answer to your research question that has not yet been tested. For some research projects, you might have to write several hypotheses that address different aspects of your research question.

A hypothesis is not just a guess — it should be based on existing theories and knowledge. It also has to be testable, which means you can support or refute it through scientific research methods (such as experiments, observations and statistical analysis of data).

Variables in hypotheses

Hypotheses propose a relationship between two or more variables. An independent variable is something the researcher changes or controls. A dependent variable is something the researcher observes and measures.

Daily apple consumption leads to fewer doctor’s visits .

In this example, the independent variable is apple consumption — the assumed cause . The dependent variable is the frequency of doctor’s visits — the assumed effect .

Developing a hypothesis

1. Ask a question

Writing a hypothesis begins with a research question that you want to answer. The question should be focused, specific, and researchable within the constraints of your project.

Do students who attend more lectures get better exam results?

2. Do some preliminary research

Your initial answer to the question should be based on what is already known about the topic. Look for theories and previous studies to help you form educated assumptions about what your research will find.

At this stage, you might construct a conceptual framework to identify which variables you will study and what you think the relationships are between them.

3. Formulate your hypothesis

Now you should have some idea of what you expect to find. Write your initial answer to the question in a clear, concise sentence.

Attending more lectures leads to better exam results.

4. Refine your hypothesis

You need to make sure your hypothesis is specific and testable. There are various ways of phrasing a hypothesis, but all the terms you use should have clear definitions, and the hypothesis should contain:

  • The relevant variables
  • The specific group being studied
  • The predicted outcome of the experiment or analysis

5. Phrase your hypothesis in three ways

To identify the variables, you can write a simple prediction in if…then form. The first part of the sentence states the independent variable and the second part states the dependent variable.

If a first-year student starts attending more lectures , then their exam scores will improve.

In academic research, hypotheses are more commonly phrased in terms of correlations or effects, where you directly state the predicted relationship between variables.

The number of lectures attended by first-year students has a positive effect on their exam scores.

If you are comparing two groups, the hypothesis can state what difference you expect to find between them.

First-year students who attended most lectures will have better exam scores than those who attended few lectures.

6. Write a null hypothesis

If your research involves statistical hypothesis testing, you will also have to write a null hypothesis. The null hypothesis is the default position that there is no association between the variables. The null hypothesis is written as H0, while the alternative hypothesis is H1 or Ha.

H0: The number of lectures attended by first-year students has no effect on their final exam scores.
H1: The number of lectures attended by first-year students has a positive effect on their final exam scores.

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What is a Hypothesis?

A hypothesis can be defined as an assumption statement that is made on the basis of evidence so that this assumption can be tested to see if it might be true. It describes what you expect will happen in your research study before it has taken place and is therefore a prediction that you are trying to explore. Certain research studies may involve several hypotheses in cases where multiple aspects of the research question want to be studied.

Hypotheses often propose an association between two or more variables: this includes the independent variable (the variable that the researcher controls/manipulates) and the dependent variable (the variable that the researcher observes and measures).

How to Write a Hypothesis

Use the following six steps to effectively create a hypothesis for your research study:

Ask a Question

The first step in writing a hypothesis is asking a question. In this step, you must clearly outline the research question that you want to answer, keeping it specific and focused.

Gather Research

Once you’ve defined your research question, you can start collecting preliminary research. Data collected at this stage can come in the form of existing studies with similar topics, academic journals, and any preliminary primary research conducted such as your own observations and experiments.

At this stage you can even construct a conceptual framework. This is a visual representation of the expected relationship between the variables being studied.

Formulate an Answer

Once you’ve conducted your preliminary research, you can think about the ways in which you can answer the question. At this stage, your research will have allowed you to develop a stance on what you believe will be the result of the research. You must frame this answer in a clear and concise sentence.

Create a Hypothesis

In this stage, you must formulate your hypothesis. As you already have the answer to your question ready, you can create your hypothesis by including the following in your statement:

  • Relevant Variables
  • Specific Group being Studied (Who/What)
  • Predicted Outcome of the Experiment

Your hypothesis is a prediction and it should be framed as a statement, not a question.

Refine the Hypothesis

In this step, you must refine your hypothesis to ensure that it is specific and testable. Furthermore, there may be certain cases in which you are studying the difference between more than just one group or are conducting correlational research. In such cases, you must clearly state the relationships or differences that you believe you will find among the variables.

Create a Null Hypothesis

Certain studies may require statistical analysis to be conducted on the data collected. When employing the scientific method to form a hypothesis, you must know the difference between the null hypothesis and the alternative hypothesis.

  • A null hypothesis is a type of hypothesis which suggests that there is no statistical relationship between the given observed variables, whether they be a single set of variables or among two sets of variables. The null hypothesis can be denoted as H 0 .

An alternative hypothesis, often denoted as H 1 , is a statement that contradicts the null hypothesis and can be considered as an alternative to the null hypothesis.

A hypothesis (plural hypotheses) is a precise, testable statement of what the researcher(s) predict will be the outcome of the study. It is stated at the start of the study.

This usually involves proposing a possible relationship between two variables: the independent variable (what the researcher changes) and the dependent variable (what the research measures).

In research, there is a convention that the hypothesis is written in two forms, the null hypothesis, and the alternative hypothesis (called the experimental hypothesis when the method of investigation is an experiment).

A fundamental requirement of a hypothesis is that is can be tested against reality, and can then be supported or rejected.

To test a hypothesis the researcher first assumes that there is no difference between populations from which they are taken. This is known as the null hypothesis. The research hypothesis is often called the alternative hypothesis.

Types of research hypotheses

Alternative Hypothesis

The alternative hypothesis states that there is a relationship between the two variables being studied (one variable has an effect on the other).

An experimental hypothesis predicts what change(s) will take place in the dependent variable when the independent variable is manipulated.

It states that the results are not due to chance and that they are significant in terms of supporting the theory being investigated.

Null Hypothesis

The null hypothesis states that there is no relationship between the two variables being studied (one variable does not affect the other). There will be no changes in the dependent variable due to the manipulation of the independent variable.

It states results are due to chance and are not significant in terms of supporting the idea being investigated.

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Nondirectional Hypothesis

A non-directional (two-tailed) hypothesis predicts that the independent variable will have an effect on the dependent variable, but the direction of the effect is not specified. It just states that there will be a difference.

E.g., there will be a difference in how many numbers are correctly recalled by children and adults.

Directional Hypothesis

A directional (one-tailed) hypothesis predicts the nature of the effect of the independent variable on the dependent variable. It predicts in which direction the change will take place. (i.e. greater, smaller, less, more)

E.g., adults will correctly recall more words than children.

Falsifiability

The Falsification Principle, proposed by Karl Popper, is a way of demarcating science from non-science. It suggests that for a theory to be considered scientific it must be able to be tested and conceivably proven false.

However many confirming instances there are for a theory, it only takes one counter observation to falsify it. For example, the hypothesis that “all swans are white,” can be falsified by observing a black swan.

For Popper, science should attempt to disprove a theory, rather than attempt to continually support theoretical hypotheses.

Can a hypothesis be proven?

Upon analysis of the results, an alternative hypothesis can be rejected or supported, but it can never be proven to be correct.

We must avoid any reference to results proving a theory as this implies 100% certainty, and there is always a chance that evidence may exist which could refute a theory.

How to write a hypothesis

    1. To write the alternative and null hypotheses for an investigation, you need to identify the key variables in the study.

What are examples of a hypothesis?

Let’s consider a hypothesis that many teachers might subscribe to: that students work better on Monday morning than they do on a Friday afternoon (IV=Day, DV=Standard of work).

Now, if we decide to study this by giving the same group of students a lesson on a Monday morning and on a Friday afternoon and then measuring their immediate recall on the material covered in each session we would end up with the following:

The null hypothesis is, therefore, the opposite of the alternative hypothesis in that it states that there will be no change in behavior.

At this point, you might be asking why we seem so interested in the null hypothesis. Surely the alternative (or experimental) hypothesis is more important?

Well, yes it is. However, we can never 100% prove the alternative hypothesis. What we do instead is see if we can disprove, or reject, the null hypothesis.

If we reject the null hypothesis, this doesn’t really mean that our alternative hypothesis is correct – but it does provide support for the alternative / experimental hypothesis.

How to reference this article:

McLeod, S. A. (2018, August 10). What is a hypothesis. Simply Psychology. www.simplypsychology.org/what-is-a-hypotheses.html

Simply Psychology’s content is for informational and educational purposes only. Our website is not intended to be a substitute for professional medical advice, diagnosis, or treatment.

The entire experiment revolves around the research hypothesis (H1) and the null hypothesis (H0), so making a mistake here could ruin the whole design.

Needless to say, it can all be a little intimidating, and many students find this to be the most difficult stage of the scientific method.

In fact, it is not as difficult as it looks, and if you have followed the steps of the scientific process and found an area of research and potential research problem, then you may already have a few ideas.

It is just about making sure that you are asking the right questions and wording your hypothesis statements correctly.

Once you have nailed down a promising hypothesis, the rest of the process will flow a lot more easily.

The Three-Step Process

It can quite difficult to isolate a testable hypothesis after all of the research and study. The best way is to adopt a three-step hypothesis; this will help you to narrow things down, and is the most foolproof guide to how to write a hypothesis.

Step one is to think of a general hypothesis, including everything that you have observed and reviewed during the information gathering stage of any research design. This stage is often called developing the research problem.

An Example of How to Write a Hypothesis

A worker on a fish-farm notices that his trout seem to have more fish lice in the summer, when the water levels are low, and wants to find out why. His research leads him to believe that the amount of oxygen is the reason – fish that are oxygen stressed tend to be more susceptible to disease and parasites.

He proposes a general hypothesis.

“Water levels affect the amount of lice suffered by rainbow trout.”

This is a good general hypothesis, but it gives no guide to how to design the research or experiment. The hypothesis must be refined to give a little direction.

“Rainbow trout suffer more lice when water levels are low.”

Now there is some directionality, but the hypothesis is not really testable, so the final stage is to design an experiment around which research can be designed, i.e. a testable hypothesis.

“Rainbow trout suffer more lice in low water conditions because there is less oxygen in the water.”

This is a testable hypothesis – he has established variables, and by measuring the amount of oxygen in the water, eliminating other controlled variables, such as temperature, he can see if there is a correlation against the number of lice on the fish.

This is an example of how a gradual focusing of research helps to define how to write a hypothesis.

The Next Stage – What to Do with the Hypothesis

Once you have your hypothesis, the next stage is to design the experiment, allowing a statistical analysis of data, and allowing you to test your hypothesis.

The statistical analysis will allow you to reject either the null or the alternative hypothesis. If the alternative is rejected, then you need to go back and refine the initial hypothesis or design a completely new research program.

This is part of the scientific process, striving for greater accuracy and developing ever more refined hypotheses.