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A-Level · Psychology

PSY.RES3 Types of Experiment: Laboratory, Field, Natural and Quasi-Experiments

AQA 7182 · Calculators not allowed · about 60 minutes

Total Marks

Name: _______________________________ Date: ____ / ____ / ______

Answer ALL questions. Show all your working.

Define a laboratory experiment in the context of psychological research, naming the typical setting and the level of control over variables.

(Total for Question 1 is 2 marks)

Define a field experiment in psychology, giving an example of the setting and stating how control compares with a laboratory experiment.

(Total for Question 2 is 2 marks)

Define a natural experiment in psychological research, and state one reason why a natural experiment might be used instead of a laboratory experiment.

(Total for Question 3 is 2 marks)

Define a quasi-experiment in psychology and state how it differs from a true experiment in terms of IV manipulation.

(Total for Question 4 is 2 marks)

Vignette: A psychology team sets up hidden speakers in a busy shopping arcade to play varying levels of background music volume and measures shoppers speed of walking past a particular shop. Participants are shoppers unaware they are in a study. Identify which type of experiment this is and justify your decision in terms of setting and control over variables.

(Total for Question 5 is 3 marks)

Vignette: A researcher compares the exam performance of two schools after a change in national exam rules, using archived exam scores from before and after the policy change. The researcher did not manipulate the policy. Identify the type of experiment and explain why the researcher cannot randomly assign participants or manipulate the IV.

(Total for Question 6 is 3 marks)

Vignette: A study compares levels of social anxiety in students born in January with students born in June, measuring responses on a social anxiety questionnaire. The researcher selects intact birth-month groups and does not allocate participants to groups. Identify the type of experiment and explain your reasoning concerning the IV.

(Total for Question 7 is 3 marks)

Vignette: In a laboratory room, volunteers are randomly assigned to wear a heavy backpack or no backpack and then complete a timed memory task. Performance is measured in seconds taken to recall a list. Identify the experiment type and state two features of the setting that support this classification.

(Total for Question 8 is 3 marks)

Distinguish between laboratory and field experiments in terms of control over extraneous variables and ecological validity, using one brief example to illustrate each point.

(Total for Question 9 is 4 marks)

Outline two ethical or practical issues that are especially relevant to conducting field experiments in public places, such as a park or shopping centre.

(Total for Question 10 is 4 marks)

Explain why natural and quasi-experiments generally provide weaker evidence for causality than laboratory experiments. Include one implication for the interpretation of results.

(Total for Question 11 is 4 marks)

Outline one advantage of laboratory experiments and one limitation of quasi-experiments with respect to generalisability and control. Give one sentence of explanation for each point.

(Total for Question 12 is 4 marks)

Discuss the strengths and limitations of laboratory experiments and natural experiments for investigating bystander intervention in public spaces. Refer to issues of control, ecological validity, ethics and the strength of causal inference in your answer.

(Total for Question 13 is 16 marks)

Mark scheme · PSY.RES3 Types of Experiment: Laboratory, Field, Natural and Quasi-Experiments

Question 1

B1 states that a laboratory experiment takes place in a controlled, artificial setting such as a research lab or classroom set up for the study oe
B1 states that the researcher has high control over variables and can manipulate the IV and control extraneous variables oe
Answer: A laboratory experiment takes place in a controlled, artificial setting (for example a research laboratory) where the researcher manipulates the independent variable and exerts high control over extraneous variables.

Question 2

B1 states that a field experiment takes place in a natural, real-world setting such as a street, school or workplace oe
B1 states that control over variables is lower than in a laboratory experiment, because the setting is less controlled oe
Answer: A field experiment is conducted in a real-world setting, such as a street, school or workplace, where the researcher manipulates the IV but has less control over extraneous variables than in a laboratory experiment.

Question 3

B1 states that a natural experiment uses an IV that varies naturally and is not manipulated by the researcher, occurring in real life oe
B1 gives a reason such as it is used when manipulation would be impractical or unethical, or when a real-world event provides the IV oe
Answer: A natural experiment studies the effect of an independent variable that varies naturally, without researcher manipulation, often used when manipulating the IV would be impractical or unethical, or when a real-world event provides the variable.

Question 4

B1 states that a quasi-experiment compares existing groups or conditions where the IV is based on an existing characteristic or situation, not randomly assigned oe
B1 states that unlike a true experiment the researcher does not directly manipulate the IV or randomly allocate participants oe
Answer: A quasi-experiment compares existing groups or conditions where the independent variable is not manipulated by the researcher and participants are not randomly allocated; the IV is based on a preexisting characteristic or situation.

Question 5

B1 identifies the design as a field experiment cao
M1 justifies by referring to a real-world natural setting (shopping arcade) where the researcher manipulates the IV (music volume) oe
A1 adds that control is lower than in a lab because participants are unaware and there are many uncontrolled extraneous variables (crowd, distractions) oe
Answer: Field experiment, because it is conducted in a real-world setting (a shopping arcade) with the researcher manipulating the independent variable (music volume) but with lower control over extraneous factors than in a laboratory.

Question 6

B1 identifies the design as a natural experiment cao
M1 explains that the IV (the policy change) varied naturally and was not under the researcher's control oe
A1 states that participants cannot be randomly assigned because the policy applies to existing schools and time periods, not to randomly allocated individuals oe
Answer: Natural experiment, because the independent variable is a real-world policy change that the researcher did not manipulate, and random assignment is impossible since the policy applies to existing schools and time periods rather than to randomly allocated participants.

Question 7

B1 identifies the design as a quasi-experiment cao
M1 explains that the IV (birth month) is an existing characteristic and not manipulated by the researcher oe
A1 notes that because the researcher does not randomly assign participants, there may be confounding participant variables between the groups oe
Answer: Quasi-experiment, because the independent variable is an existing characteristic (birth month) that the researcher does not manipulate, and participants are not randomly assigned, so participant variables may confound the comparison.

Question 8

B1 identifies the design as a laboratory experiment cao
M1 states a feature: random allocation to conditions and researcher manipulation of the IV (backpack) oe
A1 states a feature: controlled, artificial setting where extraneous variables can be minimised, such as a lab room with standardised instructions oe
Answer: Laboratory experiment. Features supporting this are random allocation to conditions with researcher manipulation of the IV (backpack), and a controlled, artificial laboratory setting with standardised procedures to minimise extraneous variables.

Question 9

M1 states that laboratory experiments have high control over extraneous variables, allowing better internal validity oe
A1 gives a brief example: a memory test in a lab with standardised lists and timing to control confounds oe
M1 states that field experiments have lower control over extraneous variables but higher ecological validity because they occur in real-world settings oe
A1 gives a brief example: varying shop music volume in a real store to measure shopper behaviour, which is more natural but has many uncontrolled influences oe
Answer: Laboratory experiments offer high control over extraneous variables and so stronger internal validity, for example a lab memory test with identical lists and timing. Field experiments have lower control but higher ecological validity because they occur in natural settings, for example manipulating shop music in a real store to measure shopper behaviour, but many other factors may influence results.

Question 10

M1 identifies an issue such as lack of informed consent or covert observation oe
A1 explains why this is a concern, e.g. participants are unaware they are studied so consent and autonomy are compromised, and this may cause distress or privacy invasion oe
M1 identifies a second issue such as safety, disruption to the public, or difficulty in debriefing participants oe
A1 explains the practical consequence, e.g. logistical difficulties obtaining permission from venues, inability to contact participants later for debriefing, or risk of causing upset or safety hazards oe
Answer: Issues include lack of informed consent or covert observation, which compromises participant autonomy and privacy because people do not know they are part of research, and practical problems such as difficulty obtaining venue permission, inability to debrief or contact participants afterwards, and potential disruption or safety risks to the public.

Question 11

M1 states that in natural and quasi-experiments the IV is not manipulated by the researcher and random allocation is absent oe
A1 explains that without manipulation and random assignment there may be confounding variables and participant differences that could cause the observed effect oe
M1 states that this reduces internal validity and makes causal claims less secure oe
A1 gives an implication, e.g. results are correlational in effect and researchers should be cautious about claiming that the IV caused the DV, suggesting further controlled studies are needed oe
Answer: Because the researcher does not manipulate the IV and participants are not randomly allocated in natural and quasi-experiments, confounding variables and preexisting differences may explain observed effects. This reduces internal validity and weakens causal inference, so findings should be interpreted with caution and often seen as correlational rather than definitive proof of causation.

Question 12

M1 advantage: laboratory experiments have high control which improves internal validity and replicability oe
A1 explanation: controlling extraneous variables and standardising procedures reduces alternative explanations and allows replication across studies oe
M1 limitation: quasi-experiments have limited generalisability because groups are not randomly selected and may not represent the wider population oe
A1 explanation: preexisting group differences or context-specific characteristics may limit how far results apply to other people or settings oe
Answer: Advantage of lab experiments: high control over variables improves internal validity and makes replication easier, because standardised procedures reduce alternative explanations. Limitation of quasi-experiments: limited generalisability, because preexisting group differences and lack of random sampling mean findings may not apply to other populations or settings.

Question 13

Level 4 (13-16): Knowledge of laboratory and natural experiments is accurate and detailed. Discussion evaluates strengths and limitations for investigating bystander intervention, with sustained, balanced consideration of control, ecological validity, ethics and causal inference. Arguments are well developed and applied to the context of public-space bystander research. Specialist terms are used appropriately and the answer is coherent and well organised.
Level 3 (9-12): Knowledge of the two experiment types is clear with some detail. Discussion evaluates strengths and limitations relevant to bystander intervention, but may be uneven in depth or balance. Application to the context is present and generally effective. The answer is organised and uses relevant terminology.
Level 2 (5-8): Knowledge is limited or partial. Discussion is mostly descriptive with limited evaluation, and links to the bystander intervention context are brief or underdeveloped. Some relevant points are made but depth and organisation are lacking. Terminology is used inconsistently.
Level 1 (1-4): Knowledge is very limited. Discussion is superficial or a list of unconnected points. Little or no application to the bystander intervention context. The answer lacks structure and relevant terminology.
Level 0 (0): No creditable content.
Indicative content:
- AO1: Laboratory experiments would take place in an artificial setting where the researcher manipulates the IV, for example staging a simulated emergency in a controlled room and varying presence of bystanders.
- AO1: Natural experiments would compare situations where the IV varies naturally, for example comparing intervention rates before and after a real public safety campaign or using naturally occurring variations in crowd density at events, with no researcher manipulation.
- AO1: Control in lab experiments is high, allowing standardisation of scenario, precise timing, clear operationalisation of the IV and reduction of extraneous variables, which supports internal validity and replicability.
- AO3: High control in labs supports stronger causal inference, because random allocation and manipulation reduce alternative explanations, but the artificiality may change participants' behaviour compared with real public spaces.
- AO3: Ecological validity is higher for natural experiments because events occur in real public settings and behaviour is observed in situ, making findings more generalisable to real-world bystander behaviour.
- AO3: Natural experiments provide weaker causal evidence because the researcher does not manipulate the IV and cannot randomly allocate participants, so confounding variables, such as differences in crowd composition or context, may explain observed differences in intervention rates.
- AO3: Ethics differ: lab experiments can obtain informed consent and debrief participants, but staging emergencies raises ethical problems about deception and distress; careful safeguards are required and some deceptions may still be judged unethical.
- AO3: Natural experiments can avoid deception because they study real events, reducing some ethical concerns, but they raise issues of consent if individuals are observed without knowledge and practical difficulties in debriefing or anonymising data from public behaviour.
- AO3: Practical issues include feasibility and control of safety: lab studies allow controlled risk management, whereas natural studies may expose participants to real danger or rely on rare events, limiting research opportunities and replicability.
- AO3: Methodological triangulation: combining lab and natural data can strengthen conclusions, for example using lab findings to test causal mechanisms and natural studies to check ecological validity, with converging evidence improving confidence.
- AO3: Examples and application: reference to classic bystander research approach, noting how laboratory replications can reveal causal mechanisms like diffusion of responsibility but natural observations of street incidents provide evidence of how often and under what conditions intervention occurs in real life.
- AO3: Conclude with balanced judgement: for investigating mechanisms and establishing causality lab experiments are stronger, but for understanding actual public behaviour natural experiments are more ecologically valid and ethically feasible in some cases; a mixed approach is often recommended.

Types of Experiment: Laboratory, Field, Natural and Quasi-Experiments - Worksheets, Questions and Revision