A hypothesis is a clear, testable prediction about the relationship between variables. It turns a research question into something you can test with data, and it underpins most quantitative research. This complete UK guide explains what a hypothesis is, the difference between null and alternative hypotheses, how to write a testable one, and how hypotheses relate to research questions and variables.
What Is a Hypothesis?
A hypothesis is a testable statement predicting a relationship between variables — for example, that one factor affects another. It is specific and falsifiable: you can gather data to support or reject it.
Null vs Alternative Hypotheses
Quantitative research uses two. The null hypothesis (H0) states there is no effect or relationship; the alternative hypothesis (H1) states there is. Statistical testing assesses whether you can reject the null in favour of the alternative.
Independent and Dependent Variables
A good hypothesis names the variables clearly. The independent variable is what you change or compare; the dependent variable is what you measure. The hypothesis predicts how the first affects the second.
Writing a Testable Hypothesis
✓ State a clear prediction.
✓ Name the variables.
✓ Make it specific and measurable.
✓ Ensure it is falsifiable.
A vague or untestable statement is not a hypothesis.
Hypothesis vs Research Question
A research question asks what you will investigate; a hypothesis predicts the answer in testable form. Quantitative studies often use hypotheses; qualitative studies usually use questions. See our research question guide.
Common Mistakes and Tips
✓ A vague, untestable statement.
✓ No clear variables.
✓ Predicting more than one relationship at once.
✓ Confusing it with a question. Tip: make it specific, measurable and falsifiable, with clear variables.
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Frequently Asked Questions
What is a hypothesis?
A clear, testable prediction about the relationship between variables.
What is the null hypothesis?
A statement that there is no effect or relationship between the variables.
What is the alternative hypothesis?
A statement that there is an effect or relationship between the variables.
What is an independent variable?
The factor you change or compare in a study.
What is a dependent variable?
The outcome you measure, which the independent variable may affect.
How do I write a testable hypothesis?
State a specific, measurable, falsifiable prediction naming the variables.
What is the difference between a hypothesis and a research question?
A question asks what you will investigate; a hypothesis predicts the answer in testable form.
Do all studies need a hypothesis?
No — quantitative studies often do; qualitative studies usually use research questions.
Related Study Guides
How to Write a Research Question • How to Write a Methodology • How to Write a Dissertation • How to Write a Lab Report
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