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Research in psychology begins with a question or an observation about human behaviour. Before conducting any study, psychologists must formulate clear, testable statements about what they expect to find. These statements are called hypotheses.
A hypothesis is a clear, testable, predictive statement about the expected outcome of a study. It is not a question — it is a statement that can be tested through research and either supported or refuted by the evidence.
flowchart TD
A[Hypothesis] --> B["Alternative<br/>H1"]
A --> C["Null<br/>H0: no difference / chance"]
B --> D["Directional<br/>one-tailed: predicts which way"]
B --> E["Non-directional<br/>two-tailed: predicts a difference"]
D --> D1["Use when prior research<br/>suggests a clear direction"]
E --> E1["Use when evidence is mixed<br/>or area is under-researched"]
The alternative hypothesis (H₁ or Hₐ) states that there will be a difference, relationship, or effect. This is what the researcher expects to find.
There are two forms:
Directional (one-tailed) hypothesis — predicts the direction of the difference or relationship:
Non-directional (two-tailed) hypothesis — predicts that there will be a difference but does not specify the direction:
The null hypothesis (H₀) states that there will be no difference, relationship, or effect — any observed difference is due to chance.
| Type | When to Use | Example |
|---|---|---|
| Directional | When previous research or theory suggests a clear direction for the result | "Students with growth mindset will score higher..." |
| Non-directional | When the area is under-researched or previous findings are contradictory | "There will be a difference in scores..." |
Operationalisation means defining variables in a way that can be measured and tested. Vague terms must be made specific.
| Vague Term | Operationalised Version |
|---|---|
| "Memory" | Score on a 20-word recall test |
| "Anxiety" | Score on a standardised anxiety questionnaire (e.g. State-Trait Anxiety Inventory) |
| "Intelligence" | Score on a standardised IQ test |
| "Aggression" | Number of aggressive acts observed in a 10-minute period |
Exam Tip: Always operationalise variables in your hypotheses. Instead of "Stress affects memory," write "Participants who complete a stressful task (giving a speech to strangers) will recall fewer words from a 20-word list than participants who complete a non-stressful task (reading quietly)."
An aim is a general statement of what the study intends to investigate. A hypothesis is a specific, testable prediction.
| Feature | Aim | Hypothesis |
|---|---|---|
| Specificity | General | Specific and testable |
| Example | "To investigate whether sleep affects memory" | "Participants who sleep for 8 hours will recall more words from a 20-word list than participants who sleep for 4 hours" |
The type of hypothesis you write depends on the research method. Experiments use hypotheses that predict a difference between conditions. Correlational studies use hypotheses that predict a relationship between variables. Observations and case studies may use more tentative, exploratory statements rather than formal hypotheses.
Before writing any hypothesis, ask: what kind of study is this? Only then can you pick the correct form of words. Confusing a difference hypothesis with a correlational one is a common exam error that loses easy marks.
Students who review past paper mark schemes often notice that examiners award the most credit for hypotheses that: specify participants, operationalise both variables, state the direction (when justified), and avoid explanatory language. Memorise these requirements and apply them every time.
Below are five research aims. For each, note how we move from a general aim to a fully operationalised hypothesis.
Aim 1: To investigate whether chewing gum helps concentration. Directional hypothesis: Participants who chew a single piece of spearmint gum during a 10-minute proof-reading task will identify more spelling errors than participants who complete the same task without chewing gum.
Aim 2: To investigate whether sleep deprivation affects reaction time. Directional hypothesis: Participants who have slept fewer than 5 hours will have slower mean reaction times (in milliseconds) on a computer reaction test than participants who have slept 8 hours or more.
Aim 3: To investigate whether background noise affects reading comprehension. Non-directional hypothesis: There will be a difference in scores on a 10-item reading comprehension test between participants who read in silence and participants who read with background office noise at 55dB.
Aim 4: To investigate the relationship between exercise and mood. Correlational (directional) hypothesis: There will be a positive correlation between the number of minutes of moderate exercise per week and total score on a 10-item mood questionnaire.
Aim 5: To investigate whether gender affects willingness to help strangers. Null hypothesis: There will be no significant difference in the proportion of male and female participants who help a confederate pick up dropped shopping within 30 seconds. Any observed difference is due to chance.
Working through examples like this builds the habit of moving from vague aims to specific, testable hypotheses — a core skill on AQA Paper 1.
Students often lose marks on hypothesis-writing questions for predictable reasons. Avoid the following errors:
Use this checklist whenever you write a hypothesis:
So far we have focused on experimental hypotheses, which predict a difference between conditions. However, when the research method is a correlation, the hypothesis must instead predict a relationship between two co-variables, not a difference.
Directional correlational hypothesis: There will be a positive correlation between the number of hours of revision per week and GCSE exam scores in Year 11 students.
Non-directional correlational hypothesis: There will be a correlation between the number of hours of revision per week and GCSE exam scores in Year 11 students.
Null correlational hypothesis: There will be no significant correlation between the number of hours of revision per week and GCSE exam scores. Any correlation observed is due to chance.
Notice the wording shifts from "higher/lower than" to "positive/negative correlation" — a small but essential change that examiners look for.
Dr Evans is interested in whether exercise improves mood. She wants to design a laboratory experiment to test this in 16-year-olds. Let's walk through the full process.
Step 1 — Identify the IV and DV. The IV is the amount of exercise. The DV is the participants' mood.
Step 2 — Operationalise. "Exercise" and "mood" are both too vague. She operationalises the IV as: 15 minutes of brisk walking on a treadmill (at 6 km/h) vs 15 minutes of seated reading. She operationalises the DV as the total score on a 10-item self-report mood scale (items scored 1-5, total 10-50), completed immediately after the activity.
Step 3 — Choose a sampling method. She considers random sampling (unbiased but hard to access a full population list) and opportunity sampling (convenient but biased). Because her budget is limited, she uses opportunity sampling from the college common room and acknowledges this as a limitation of generalisability.
Step 4 — Choose an experimental design. Because she worries about order effects (an energetic walk may influence the seated condition), she uses an independent groups design with random allocation to conditions.
Step 5 — Write a directional hypothesis. Previous research consistently shows exercise improves mood, so a directional (one-tailed) prediction is justified: Sixteen-year-old participants who complete 15 minutes of brisk treadmill walking at 6 km/h will record higher total scores on the 10-item mood scale than participants who complete 15 minutes of seated reading.
Step 6 — Write the null hypothesis. There will be no significant difference in total mood scores on the 10-item scale between participants who complete 15 minutes of brisk treadmill walking and those who complete 15 minutes of seated reading. Any difference is due to chance.
Step 7 — Ethics (BPS). Dr Evans obtains informed consent from participants and a parent or guardian (participants are under 18 at some colleges). She explains the right to withdraw, screens out anyone with cardiovascular conditions to ensure protection from harm, stores data anonymously to protect confidentiality, and provides a debrief with information on support services in case any participant is distressed.
This example shows how a good hypothesis flows from operationalised variables and is supported by a carefully chosen design and ethical safeguards.
Misconception: "A non-directional hypothesis is the same as a null hypothesis."
They are very different. A non-directional (two-tailed) hypothesis predicts that there will be a difference, but does not say which way — e.g. "There will be a difference in test scores between the two groups." A null hypothesis predicts that there will be no difference at all, or that any observed difference is due to chance. Both are stated alongside each other in a well-designed study: the researcher tests whether the evidence is strong enough to reject the null in favour of the alternative (which may be directional or non-directional).
Question: "A psychologist is investigating whether chewing gum improves memory. Write a directional hypothesis for this study." (3 marks)
Grade 3-4 response: Chewing gum makes memory better.
The idea is broadly correct but there is no mention of participants, no operationalisation of "memory," and no measurable outcome. Likely 1 mark.
Grade 5-6 response: Participants who chew gum will remember more words on a memory test than participants who do not chew gum.
The hypothesis is directional and includes both conditions, but "memory test" is not fully operationalised (how many words? how long?). Likely 2 marks.
Grade 7-9 response: Participants who chew a stick of spearmint gum for 5 minutes while learning a list of 20 words will correctly recall more words on a written free-recall test taken immediately afterwards than participants who learn the same list for 5 minutes without chewing gum.
Fully operationalised: both conditions are clearly specified, the DV is quantified (number of correctly recalled words), and the direction of the prediction is unambiguous. Full 3 marks.
This content is aligned with the AQA GCSE Psychology (8182) specification, Research methods. For the most accurate and up-to-date information, please refer to the official AQA specification document.