Naturally occurring IV, not manipulated
A natural experiment measures the effect of a naturally occurring IV the researcher does not manipulate — a real difference or event like a flood, a law change or an upbringing. Because the IV already exists, participants are not randomly allocated. A DV is still measured, so it is an experiment, not an observation. A definition needs the naturally occurring IV and that the researcher measures the DV; 'in a natural environment' alone earns little.
Strengths and weaknesses: no control of IV
Every strength and weakness flows from one fact: the researcher does not control the IV. Strengths: high ecological validity; it can study what is too unethical or impractical to manipulate; and demand characteristics are reduced. Weaknesses: cause and effect is hard, as uncontrolled extraneous variables may explain results; no random allocation, so groups may differ; a rare event is hard to replicate. Realism over control.
Defined by the IV, not the setting
The commonest way to lose marks is to define a natural experiment by its setting not by who controls the IV. A field experiment is also in the real world, but the researcher manipulates the IV there. A natural experiment can even run in a lab — left- and right-handed people measured for reaction times is still natural, as handedness was not manipulated. The test is not the setting but 'did the researcher manipulate the IV, or did it vary naturally?'
Drawn from real examiner reports.
Not a field experiment or an observation
This is the signature error. Not a field experiment: both are in the real world, but a field experiment manipulates the IV, whereas a natural experiment's IV occurs naturally — the distinction is control of the IV, not the setting. Not an observation: a natural experiment has an IV and DV; an observation records behaviour with no IV.
June 2022 P2 Q5
Don't drift into the study's content
When a natural experiment is the 12-mark Evaluate, the question is about the method, not the topic. Candidates who wrote about the subject matter — say, television and eating disorders — scored poorly. Keep every point on the method: the naturally occurring IV, weak control, validity and ethics. Use the study as evidence about the method, not a retelling.
June 2022 P2 Q5
AO1 stops at 'a natural environment'
Examiners report AO1 is the weakest objective: candidates make one point and stop. 'It happens in a natural environment' misses the top band. Developed AO1 explains the features: the IV occurs naturally, unmanipulated, a DV is measured, participants not randomly allocated, extraneous variables hard to control. Aim for two or three, not one label.
June 2022 P2 Q5; June 2023 P2 Q5; June 2024 P2 Q6
'Explain' a strength is not 'describe' it
'Explain a strength' is not 'describe': identification without justification is penalised. Naming a feature earns little; marks come from why it is a strength and its effect. Weak: 'a strength is high ecological validity.' Full: the IV is a real event, so behaviour is realistic (why) and generalises (consequence). Likewise for a weakness.
June 2023/2024 P2 Summaries
AO3 needs AO2 — link to the study
On a scenario the dependency rule bites: AO3 cannot be awarded without AO2. An evaluation that never uses the study's detail scores nothing. Naming the researcher or repeating the stem is not application; specifics are — 'the groups fell naturally, so income and schooling were uncontrolled and may explain the difference'. A general point with no link scores zero.
June 2023 P2 Q31
'Natural' describes the IV, not the place
Because it is called a 'natural' experiment, students think the word describes the place and means outdoors. It describes the IV, which is unmanipulated. Measuring can happen anywhere — bringing naturally occurring groups (say bilingual people or not) into a laboratory is still natural, as the IV was not manipulated. Look at the IV, not the room.
Top band on the 12-mark Evaluate
The 12-mark 'Evaluate' has three objectives. AO1: the features — IV occurs naturally, DV measured, no random allocation, weak control. AO2: classify the study, say why. AO3: several balanced, linked issues (validity, control, ethics), then conclude.
AO2: classify the study, say why
AO2 means applying the study, not rewording it. Best answers classify it as a natural experiment and say why, naming its naturally occurring IV and DV, then keep using that detail. Rewording the scenario collapses AO2, capping the answer since AO3 depends on it.
'Describe the difference' needs a connective
'Describe the difference' (natural vs field): two separate definitions score only one mark. The second needs a connective — 'a field experiment changes the IV, whereas a natural one changes by itself.' One comparative sentence, not two.
A natural experiment is a research method in which the independent variable (IV) is not manipulated by the researcher but occurs naturally, and the researcher measures its effect on the dependent variable (DV).
Natural experiment — an experiment in which the IV occurs naturally (the researcher could not or did not manipulate it) and the researcher measures its effect on the DV.
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