What does Unit 4 of WJEC A-Level Psychology cover?

Unit 4, Psychology: Applied Research Methods, has two sections. Section A is personal investigations: the practical studies you carry out across the course (such as a Stroop or memory experiment, an observation and a correlation) and the research skills they build. Section B is the application of research methods: brain-scanning techniques, longitudinal and cross-sectional studies, extended reliability and validity, distributions and descriptive statistics, and choosing and interpreting inferential tests.

How is Unit 4 examined in WJEC A-Level Psychology?

A2 Unit 4, Psychology: Applied Research Methods, is a written exam of 1 hour 30 minutes worth 60 marks, which is 20 percent of the full A level. It applies research methods to scenarios, so expect questions on design, statistics and evaluation built around described studies, including choosing and interpreting an inferential test. The personal investigations are assessed through these questions, not as a separate coursework folder.

How do I choose the right inferential test?

Ask three questions about the study: are you testing a difference or a correlation; is the design related (repeated measures or matched pairs) or unrelated (independent groups); and what is the level of data (nominal, ordinal or interval)? For example, a test of difference with a related design and ordinal data points to the Wilcoxon test; difference, unrelated, ordinal points to Mann-Whitney; correlation with ordinal data points to Spearman's rho; and nominal, unrelated points to chi-square.

What does a significance level of p is less than or equal to 0.05 mean?

It means there is a 5 percent (1 in 20) probability that the result is due to chance. It is the standard significance level in psychology. When a result reaches p is less than or equal to 0.05 it is statistically significant, so the null hypothesis is rejected and the alternative hypothesis is accepted. A more stringent level such as 0.01 is used when greater certainty is needed.

What is the difference between longitudinal and cross-sectional studies?

A longitudinal study follows the same participants over a long period, so it can show genuine change and development and controls participant variables, but it is slow and prone to attrition. A cross-sectional study compares different groups (such as different ages) at one point in time, so it is quicker and avoids attrition, but group differences may reflect cohort effects rather than development.

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WJEC A-Level Psychology Unit 4 Psychology: Applied Research Methods: a deep dive on personal investigations and applied methods

A deep-dive WJEC A-Level Psychology guide to Unit 4, Psychology: Applied Research Methods. Covers Section A personal investigations and Section B applied research methods (brain scans, longitudinal and cross-sectional studies, reliability and validity, distributions and inferential tests), and how the A2 Unit 4 paper is structured and marked.

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Jump to a section

What Unit 4 actually demands
Section A: personal investigations
Section B: applied research methods
How Unit 4 is examined
Check your knowledge

What Unit 4 actually demands

Psychology: Applied Research Methods is the course's most quantitative unit. It has two sections. Section A personal investigations: the practical studies you carry out across the course and the research skills they build. Section B applied research methods: the extended, scenario-based methods and statistics, including brain scans, longitudinal and cross-sectional designs, reliability and validity, distributions and descriptive statistics, and inferential tests. It is an A2 unit, and the statistics must be secure.

This guide maps both sections, then sets out the exam patterns WJEC repeats. Each topic has a matching dot-point page with practice questions; this overview ties them together.

Section A: personal investigations

Across the course you run small studies that span the main methods: an experiment (such as the Stroop effect or a memory study), an observation, a questionnaire and a correlation. They build the skills of designing (hypotheses, variables, design, sampling, ethics), analysing (descriptive and inferential statistics), reporting (the standard sections) and evaluating (reliability, validity, ethics and improvements). These skills are then examined in the Unit 4 paper, often through a described study, rather than submitted as a marked folder.

Section B: applied research methods

The applied content extends the Unit 2 toolkit:

Brain-scanning techniques. fMRI (blood oxygen, good spatial detail), PET (tracer, used by Raine 1997) and EEG (electrical activity, good time resolution), plus their strengths and limits.
Longitudinal and cross-sectional studies. Following the same people over time versus comparing groups at one time.
Extended reliability and validity. Test-retest, split-half and inter-rater reliability; internal, ecological, population and temporal validity.
Distributions and descriptive statistics. The normal distribution and skew; measures of central tendency (mean, median, mode) and dispersion (range, standard deviation); appropriate graphs.
Inferential tests. Choosing the test from the design, the level of data and difference-or-correlation, and interpreting significance against p is less than or equal to 0.05.

How Unit 4 is examined

A2 Unit 4 is a 1 hour 30 minute written paper worth 60 marks (20 percent of the A level). A typical profile:

Scenario questions. A described study to analyse: identify the design and variables, write a hypothesis, control extraneous variables, and evaluate the methodology.
Statistics questions. Calculating or interpreting descriptive statistics, choosing the correct inferential test, and explaining significance.
Applied-methods questions. On brain scans, longitudinal versus cross-sectional designs, and reliability and validity.

Check your knowledge

A mix of methods and statistics questions. Attempt them under timed conditions, then check against the solutions.

Name the two sections of Unit 4. (2 marks)
Name three brain-scanning techniques. (3 marks)
State the three questions used to choose an inferential test. (3 marks)
What does a significance level of p is less than or equal to 0.05 mean? (2 marks)
Give one strength and one weakness of a cross-sectional study. (2 marks)
Which measure of central tendency is best for skewed data, and why? (2 marks)
Identify the inferential test for a test of difference with a related design and ordinal data. (1 mark)
Explain how a researcher could improve the reliability of an observation. (3 marks)

Solutions

Q1: Section A personal investigations and Section B application of research methods.
Q2: Any three: fMRI, PET and EEG.
Q3: Are you testing a difference or a correlation; is the design related or unrelated; and what is the level of data (nominal, ordinal or interval)?
Q4: There is a 5 percent (1 in 20) probability the result is due to chance; it is the standard significance level, at which the null hypothesis is rejected.
Q5: Strength: it is quick and avoids attrition because groups are compared at one time. Weakness: differences may reflect cohort effects rather than genuine development.
Q6: The median, because it is not distorted by the extreme scores (outliers) that pull the mean towards the tail in a skewed distribution.
Q7: The Wilcoxon signed-ranks test.
Q8: Use two or more observers and check inter-rater reliability, with clearly operationalised behavioural categories and training, so observers record the same behaviour consistently.