Natural Experiments

Experiments look for the effect that manipulated variables (independent variables, or IVs) have on measured variables (dependent variables, or DVs), i.e. causal effects.

Natural experiments are studies where the experimenter cannot manipulate the IV, so the DV is simply measured and judged as the effect of an IV. For this reason, participants cannot be randomly allocated to experimental groups as they are already pre-set, making them quasi-experiments. For instance, an experiment might investigate the relative levels of aggression observed in boys and girls in a primary school (the experimenter cannot manipulate who belongs to the ‘boy’ and ‘girl’ groups).

Evaluation of natural experiments:

Strengths

- The natural settings where such experiments take place mean that results will have high ecological validity (i.e. they should relate well to real life behaviour).

- Demand characteristics are often not a problem, unlike laboratory experiments (i.e. participants are less likely to adjust their natural behaviour according to their interpretation of the study’s purpose, as they might not know they are taking part in a study).

Weaknesses

- Being unable to randomly allocate participants to conditions means that sample bias may be an issue (e.g. other extraneous variables that change with the pre-set IV group differences may confound the results, meaning a causal IV-DV effect is unlikely).

- Ethical issues such as lack of informed consent commonly arise, as deception is often required; debriefing, once the observation/experiment has ended, is necessary.