Write and apply research hypotheses
Turn a research question into a testable null hypothesis or a directional or non-directional alternative with clear variables.
Exam scope and assessment notes
Original StudyForA teaching mapped to the Cambridge 2028–2030 syllabus. These lessons are independent study support, not Cambridge material, official mark schemes or awarded grades. No lesson reproduces a research article or Cambridge question. Human subject-expert review and full timed-paper grading remain pending. This is one of the five additional A Level methodology areas and supports Paper 4 planning; it does not replace teaching the selected specialist options or a timed Paper 4 practice set.
Before you begin
- This lesson supports the 2028–2030 Version 1 A Level Psychology route. Review the AS research-method foundations first, then apply the method to the specialist options your school selects.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
A hypothesis predicts that notification exposure and recall will be related, without saying in which direction. What type is it?
What you will learn
- Write a null hypothesis about no predicted difference or relationship
- Write one-tailed directional and two-tailed non-directional alternatives
- Match a hypothesis to the method, population and operationalised variables
Begin with an aim and measurable variables
An aim states what a study investigates. Before writing a hypothesis, define who is studied, which conditions or co-variables are compared, and how the outcome is measured.
A hypothesis predicts a pattern that can be checked against data. Operational definitions make it clear what counts as each condition and outcome; broad claims such as 'attention will improve' need a specified task and scoring rule.
Null and alternative hypotheses make different predictions
A null hypothesis predicts no difference between specified conditions or no relationship between specified co-variables in the population. Avoid claiming that a study proves a universal absence of an effect.
An alternative hypothesis predicts a difference or relationship. A directional, one-tailed hypothesis states which group is expected to score higher or whether the relationship is positive or negative. A non-directional, two-tailed hypothesis predicts a difference or relationship without selecting its direction.
Choose direction before examining the outcome
Use a directional prediction only when theory or prior evidence justifies a specific direction before the data are observed. Otherwise, a non-directional prediction avoids choosing a direction after seeing which result occurred.
Match the wording to the design. An experiment may predict a difference between conditions; a correlational study predicts a relationship between co-variables and cannot, by itself, show that one causes the other. A clear hypothesis does not guarantee that the prediction will be supported.
Sources for this lesson
Pause and explain
Which statement is suitable for a correlational study of practice time and test score?
Worked example
A researcher compares recall after quiet study and study with notifications. Write one non-directional alternative and its null hypothesis.
Show the worked solution
- Define the two revision conditions and a recall measure.
- The alternative must say 'a difference' without predicting which condition scores higher.
- The null must predict no difference in the measured outcome.
Answer Alternative: There will be a difference in the number of words correctly recalled after quiet study and after study with notifications. Null: There will be no difference in the number of words correctly recalled after the two study conditions.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
A researcher measures the number of words recalled after quiet revision or revision with phone notifications. Write a directional alternative hypothesis predicting fewer recalled words with notifications.
Give me a hint
Name both conditions and the measurable score.
Compare my reasoning
- Specify the participants or sample being studied.
- Define the outcome as the number of list words recalled correctly after the same interval.
- State the predicted direction between notification and quiet conditions.
Among the sampled learners, those revising with phone notifications will recall fewer list words correctly after the fixed interval than those revising in quiet.
Look for these in your work
- Conditions compared
- Recall outcome is operationalised
- Direction is explicit
A study finds a positive correlation between weekly sleep duration and recall score. Write a suitable non-directional alternative and explain one limit.
Give me a hint
Use the term 'relationship'; do not describe an assigned condition.
Compare my reasoning
- Name both co-variables: weekly sleep duration and recall score.
- Predict that a relationship exists without selecting its direction.
- State that correlation alone cannot show whether sleep caused score differences or another factor affected both.
There will be a relationship between weekly sleep duration and recall score among the sampled learners. The correlation cannot establish that sleep duration caused the scores; factors such as health or workload may relate to both.
Look for these in your work
- Both co-variables named
- Non-directional prediction used
- Causal limit stated
A school wants to know whether a new optional retrieval-practice routine changes the number of correct answers on a short quiz. Write a null and one justified alternative.
Give me a hint
Define the compared conditions and the same quiz outcome first.
Compare my reasoning
- Compare routine users with a clearly defined usual-practice group, or specify a repeated-measures plan.
- Define outcome as number of correct answers on the same quiz under the same time limit.
- State no difference for the null; choose a directional alternative only if prior evidence supports a direction, otherwise make it non-directional.
Null: There will be no difference in the number of correct answers between learners assigned to the retrieval-practice routine and learners using usual practice. A non-directional alternative is that there will be a difference. Use a one-tailed alternative only when a justified prediction is set in advance.
Look for these in your work
- Conditions and outcome defined
- Null predicts no difference
- Alternative direction is justified or left open
Common mistakes
- Writing an aim as if it were a hypothesis
- Leaving the population or measure too vague to test
- Calling a correlational relationship a causal effect
- Choosing a directional hypothesis after inspecting the results
- Using 'no effect' without specifying the conditions and outcome
What can you explain now?
What extra prediction does a directional alternative make?
Compare with the explanation
It states the expected direction of a difference or relationship, not merely that one exists.
The direction should be justified before the researcher sees the outcome data.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
How do null, directional alternative and non-directional alternative hypotheses differ, and why must a hypothesis fit the research design?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.