How do psychologists select participants, and what ethical principles must they follow?
Sampling (target population, sample, random, opportunity, volunteer, systematic and stratified sampling; bias and generalisability) and ethics (the BPS principles: informed consent, deception, right to withdraw, protection from harm, confidentiality, and dealing with ethical issues).
An Eduqas A-Level Psychology answer to sampling and ethics in Component 2. Covers target populations and samples, random, opportunity, volunteer, systematic and stratified sampling, sampling bias and generalisability, and the BPS ethical principles with ways of dealing with ethical issues.
Reviewed by: AI editorial process; not yet individually human-reviewed
Have a quick question? Jump to the Q&A page
Jump to a section
What this dot point is asking
Component 2 covers sampling and ethics. You must know the sampling methods (and their bias and generalisability) and the BPS ethical principles, and be able to apply ways of dealing with ethical issues to a study.
The answer
Sampling
Ethics
Bias and generalisability
A biased sample (for example only students, or only volunteers) limits how far results apply. The more representative the sample, the more confidently the findings generalise to the target population. Larger, well-chosen samples reduce the influence of anomalies.
Examples in context
Example 1. Volunteer bias. A study advertised in a newspaper attracts people who are more motivated, curious or have spare time, so the sample is not typical. This volunteer bias limits generalisability and is a standard weakness of self-selected samples.
Example 2. Dealing with deception via debrief. If a study must briefly mislead participants about its aim to avoid demand characteristics, a full debrief afterwards (explaining the real aim and offering to withdraw data) addresses the ethical issue, showing how researchers balance validity and ethics.
Try this
Q1. Explain one strength and one weakness of volunteer sampling. [2 marks]
- Cue. Strength: it is easy and gives willing, committed participants; weakness: volunteer bias means the sample may be unrepresentative (more motivated or curious people respond).
Q2. Name three BPS ethical principles. [3 marks]
- Cue. Informed consent, the right to withdraw, protection from harm (also deception and confidentiality).
Q3. Explain how debriefing deals with an ethical issue. [2 marks]
- Cue. A debrief explains the study's true aims at the end, restores participants' understanding after any deception, and offers the right to withdraw their data.
Exam-style practice questions
Practice questions written in the style of WJEC Eduqas exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Eduqas 20186 marksA researcher recruits the first 20 students who walk into the library. Identify this sampling method and explain one strength and one weakness. [6 marks]Show worked answer →
An identification and evaluation item (AO2/AO3).
Method: opportunity sampling (selecting whoever is available and willing at the time).
Strength: it is quick, easy and convenient, so data can be gathered with little time or cost.
Weakness: it is likely to be biased and unrepresentative (here, only library-using students at one time of day), so the findings may not generalise to the wider target population.
Markers reward correct identification of opportunity sampling and a clear strength and weakness focused on convenience versus bias.
Eduqas 20218 marksExplain how a researcher could deal with the ethical issues of deception and protection from harm in a study. [8 marks]Show worked answer →
An application item on ethics (AO2/AO3).
Deception: avoid it where possible; if some deception is unavoidable (to prevent demand characteristics), keep it minimal, gain approval from an ethics committee, and fully debrief participants afterwards, explaining the true aims and offering the right to withdraw their data. Presumptive or prior general consent can also help.
Protection from harm: ensure risk is no greater than everyday life, monitor participants during the study, stop if distress occurs, remind them of the right to withdraw, and debrief, offering follow-up support if needed (for example counselling).
Markers reward practical, principle-based strategies (ethics committee, debrief, right to withdraw, monitoring) tied to each issue.
Related dot points
- The experimental method: types of experiment (laboratory, field, natural, quasi), independent and dependent variables and operationalisation, hypotheses, extraneous and confounding variables and controls, and experimental designs (independent groups, repeated measures, matched pairs).
An Eduqas A-Level Psychology answer to the experimental method in Component 2. Covers laboratory, field, natural and quasi experiments, independent and dependent variables, operationalisation, hypotheses, extraneous and confounding variables, controls, and the three experimental designs with their strengths and weaknesses.
- Non-experimental methods: observation (naturalistic, controlled, participant, non-participant, overt, covert; behavioural categories and sampling) and self-report (questionnaires and interviews; open and closed questions; designing good questions).
An Eduqas A-Level Psychology answer to observation and self-report methods in Component 2. Covers types of observation, behavioural categories, event and time sampling, questionnaires and interviews, open and closed questions, and the strengths and weaknesses of each method.
- Correlation (co-variables, positive, negative and zero correlations, correlation coefficients, scattergrams, correlation does not equal causation) and case studies (in-depth study of an individual or small group, qualitative data, strengths and weaknesses).
An Eduqas A-Level Psychology answer to correlation and case studies in Component 2. Covers co-variables, positive, negative and zero correlations, correlation coefficients and scattergrams, why correlation is not causation, and the strengths and weaknesses of case studies.
- Reliability (internal and external; test-retest, inter-observer; how to assess and improve it) and validity (internal and external; face, concurrent, ecological, temporal and population validity; demand characteristics and investigator effects; how to assess and improve it).
An Eduqas A-Level Psychology answer to reliability and validity in Component 2. Covers internal and external reliability, test-retest and inter-observer reliability, internal and external validity, face, concurrent, ecological, temporal and population validity, demand characteristics and investigator effects, and how to assess and improve each.
- The two personal investigations: designing and conducting two studies using different methods (aim and hypothesis, variables, design, sampling, ethics, procedure), analysing the data with appropriate descriptive and inferential statistics, writing up, and applying research-methods reasoning to a novel scenario.
An Eduqas A-Level Psychology answer to the two personal investigations in Component 2. Covers designing and running two studies using different methods, making the design decisions, analysing data with descriptive and inferential statistics, writing the report, and applying research-methods knowledge to an unfamiliar scenario in the exam.
Sources & how we know this
- Eduqas GCE A Level in Psychology (A290) specification — Eduqas (2015)