In random sampling, what makes it "random," and what is its main advantage?
A: Participants are selected haphazardly from whoever is available; advantage is convenience
B: Every member of the target population has an equal chance of being selected; advantage is that the sample is likely to be representative, minimising systematic bias
C: Participants are grouped by key characteristics before selection; advantage is proportional representation of subgroups
D: Participants volunteer themselves; advantage is motivation and willingness to participate
Correct: Every member of the target population has an equal chance of being selected; advantage is that the sample is likely to be representative, minimising systematic bias
Random sampling requires that every member of the target population has an equal, independent probability of being selected — typically achieved via random number generators or a random number table applied to a full list (sampling frame) of the population. Because selection is unbiased, the resulting sample tends to be representative of the population in ways the researcher did not specifically plan for — meaning findings are more likely to generalise. The main limitation is practicality: obtaining a complete sampling frame of a large population is often impossible, and random selection does not guarantee representativeness in small samples (random samples can still deviate substantially from the population by chance).
What is opportunity sampling and what is its chief limitation?
A: Selecting participants who respond to an advertisement; limitation is that volunteers may differ from the general population
B: Selecting whoever happens to be available at the time and place of the study; limitation is that the sample may be unrepresentative because it is determined by convenience rather than systematic selection
C: Selecting participants to proportionally represent subgroups; limitation is the difficulty of identifying all relevant subgroups
D: Using a random number table to select from a list; limitation is that a complete list of the population is rarely available
Correct: Selecting whoever happens to be available at the time and place of the study; limitation is that the sample may be unrepresentative because it is determined by convenience rather than systematic selection
Opportunity sampling (also called convenience sampling) involves recruiting whoever is accessible — people passing by in a shopping centre, students available in a university psychology pool, colleagues in one's workplace. It is the most commonly used method in psychology because it is quick, cheap, and requires no sampling frame. Its critical limitation is that the sample reflects whoever happened to be in that place at that time, which may systematically exclude or over-represent certain groups (e.g. university student samples over-represent young, educated, Western individuals — the so-called WEIRD problem: Western, Educated, Industrialised, Rich, Democratic). This limits the generalisability of findings to other populations.
How does stratified sampling differ from random sampling, and what problem does it solve?
A: Stratified sampling uses random allocation to conditions rather than random selection from the population; it solves order effects
B: Stratified sampling divides the population into subgroups (strata) based on relevant characteristics and then randomly selects proportional numbers from each stratum; it ensures subgroups are represented in the sample in proportion to their presence in the population
C: Stratified sampling involves sampling from multiple geographic locations; it solves the problem of geographic clustering
D: Stratified sampling selects only the most representative individuals from each group; it solves the problem of outliers
Correct: Stratified sampling divides the population into subgroups (strata) based on relevant characteristics and then randomly selects proportional numbers from each stratum; it ensures subgroups are represented in the sample in proportion to their presence in the population
Stratified sampling first divides the target population into strata — subgroups defined by characteristics relevant to the research question (e.g. age bands, gender, ethnicity, socioeconomic status) — then randomly samples from each stratum in proportion to its presence in the overall population. For example, if 60% of the population is female, 60% of the sample should be female. This ensures that random sampling will not, by chance, under-represent a key subgroup. The method produces more representative samples than simple random sampling when the strata are relevant to the variables being studied, but it requires knowledge of the population's composition and a sampling frame for each stratum.
What is volunteer (self-selected) sampling and what is the characteristic bias it introduces?
A: Participants selected by the researcher based on specific criteria; introduces selection bias toward participants who fit the study's needs
B: Participants who come forward in response to an advertisement or call for volunteers; typically introduces volunteer bias — volunteers may be more motivated, more curious, or have stronger views than non-volunteers, making the sample unrepresentative
C: Participants assigned to conditions by lottery; introduces random error that may mask systematic effects
D: Participants recruited through snowball referral; introduces social network bias
Correct: Participants who come forward in response to an advertisement or call for volunteers; typically introduces volunteer bias — volunteers may be more motivated, more curious, or have stronger views than non-volunteers, making the sample unrepresentative
In volunteer sampling, participants actively opt in — responding to a poster, email, or online post asking for research participants. The researcher exercises minimal control over who is recruited. Volunteer bias arises because the type of person who voluntarily comes forward for research tends to differ from the population at large: they may be more altruistic, more curious about psychology, more comfortable disclosing personal information, or — if they have relevant personal experience — more motivated to participate in studies on that topic. This means findings may not generalise to those who would not volunteer. However, volunteer sampling is ethical by design: participants have actively consented before the study begins, which is particularly important in studies that carry some risk.
What must be included in fully informed consent, according to ethical guidelines?
A: The researcher's name and institution, but not the study's purpose if disclosure would invalidate the research
B: Sufficient information about the study's nature, procedures, risks, and the participant's right to withdraw for the participant to make a genuinely voluntary decision about taking part
C: A legally binding contract signed by both participant and researcher
D: Disclosure of all raw data the participant will generate, so they can verify how their information is used
Correct: Sufficient information about the study's nature, procedures, risks, and the participant's right to withdraw for the participant to make a genuinely voluntary decision about taking part
Informed consent requires that participants receive enough information to make a genuinely free decision about participation. This typically includes: the study's purpose (or a non-deceptive version of it), what participation involves, any foreseeable risks or discomforts, how data will be stored and used, that participation is voluntary and can be stopped at any time, and who to contact with questions. The BPS Code of Ethics emphasises that consent must be meaningful — not buried in jargon or given under social pressure. Particular care is required for vulnerable populations (children, people with cognitive impairments) where additional safeguards (parental consent, assent alongside consent) are necessary.
A participant in a psychology study tells the researcher midway through: "I'd like to stop now." What does the ethical principle of the right to withdraw require the researcher to do?
A: Allow the participant to stop only if they can provide a reason, so the researcher can record why attrition occurred
B: Allow the participant to stop immediately without requiring a reason, and — if the participant requests it — destroy or exclude the data already collected
C: Complete the current task before allowing the participant to leave, since partial data is unusable
D: Allow the participant to stop but retain their data if it has already been anonymised
Correct: Allow the participant to stop immediately without requiring a reason, and — if the participant requests it — destroy or exclude the data already collected
The right to withdraw is unconditional: participants may stop at any time during the study without needing to give a reason, and without suffering any negative consequence (financial penalty, academic repercussion, or social pressure from the researcher). Crucially, the right extends to retrospective withdrawal — after the study ends, participants may request that their data be excluded from analysis and destroyed, even if the data collection is complete. This is particularly important when studies use deception, since participants may only fully understand what they took part in during the debrief. The right to withdraw protects participants from being trapped in distressing situations and ensures ongoing voluntariness throughout the study.
Under what conditions might deception be ethically permissible in psychological research, and what safeguard must follow?
A: Deception is never permissible under BPS guidelines, regardless of the research purpose
B: Deception may be permissible when the research question cannot be validly studied without it, when the potential knowledge gained is significant, when there is no foreseeable serious harm, and when a thorough debriefing is provided afterwards
C: Deception is permissible whenever participants are told in general that "the study involves some deception" at the start
D: Deception is permissible only in online studies where participants cannot be identified
Correct: Deception may be permissible when the research question cannot be validly studied without it, when the potential knowledge gained is significant, when there is no foreseeable serious harm, and when a thorough debriefing is provided afterwards
The BPS Code of Human Research Ethics acknowledges that some research — particularly in social psychology — cannot be conducted without deception, because revealing the true purpose would fundamentally alter participants' behaviour (as in Milgram's obedience studies, Asch's conformity studies, or any study of demand characteristics). Deception is permissible only when: the study has genuine scientific value that cannot be achieved otherwise, there is no reasonable alternative, the likely harm is minimal, the deception does not relate to risks or the nature of participation in a way that would affect whether participants consent, and ethics committee approval has been obtained. The non-negotiable safeguard is thorough debriefing immediately afterwards, allowing participants to understand what they actually took part in and providing an opportunity to withdraw their data.
What is a debriefing and what purposes does it serve?
A: A pre-study interview to establish participants' baseline knowledge of the topic
B: A post-study session in which the researcher explains the true purpose of the study, addresses any deception used, checks for distress, provides support if needed, and offers participants the opportunity to withdraw their data
C: A meeting between researchers to discuss the study's findings before publication
D: A follow-up questionnaire sent to participants several weeks after the study to measure lasting effects
Correct: A post-study session in which the researcher explains the true purpose of the study, addresses any deception used, checks for distress, provides support if needed, and offers participants the opportunity to withdraw their data
Debriefing is a structured post-study conversation between researcher and participant. Its purposes are multiple: explaining what the study was actually about (especially if deception was used), restoring any false beliefs created by the deception, assessing whether the participant experienced any distress or negative effects, providing support or referrals if they did, re-confirming consent now that participants know the full picture, and offering the option to withdraw their data. The BPS emphasises that debriefing should leave participants no worse off than before they took part. It is not a tick-box exercise — if a participant is distressed, the debrief must address this. For studies with vulnerable populations or particularly sensitive topics, more extensive follow-up support may be required.
Sampling & Ethics
In random sampling, what makes it "random," and what is its main advantage?
About this quiz
No study can include everyone — so researchers must choose who to include and how. The sampling method shapes who the findings apply to. And whoever is included must be treated with respect: psychology's ethical guidelines exist because the field's history includes experiments that caused real harm.
This quiz covers four sampling methods (random, opportunity, stratified, and volunteer) and the core ethical principles laid out by the British Psychological Society — including informed consent, the right to withdraw, deception, debriefing, and protection from harm.