Experiments are central to psychology because they allow researchers to investigate cause-and-effect relationships. AQA requires you to know what makes a study experimental and how the four main types differ.

The experimental method

Psychologists use the experimental method when they want to test whether changing one factor produces a change in behavior or experience. In an experiment, the researcher changes the independent variable and measures the dependent variable.

Diagram of a basic experiment showing the independent variable (manipulated condition) leading to the dependent variable (measured outcome). It visually encodes the core causal claim psychologists test in experiments: changing the IV should produce a change in the DV. Source

This makes experiments especially useful for studying causation, not just association.

All experiments share this basic purpose, but they differ in where the study happens and whether the researcher actually manipulates the independent variable. These differences affect how much control the psychologist has and how realistic the situation is.

Laboratory experiments

One major type is the laboratory experiment.

The key feature is control. The setting is arranged so that outside influences are reduced as much as possible. A laboratory experiment does not have to happen in a science lab; it could be any setting organized and controlled by the researcher.

Typical features include:

• carefully standardized procedures

• controlled surroundings

• precise measurement of behavior

• reduced interference from everyday distractions

This high level of control means laboratory experiments are often good for identifying cause-and-effect relationships. However, participants may behave differently because the situation feels artificial. This can reduce how far the findings reflect everyday life. For AQA, the main point is that a laboratory experiment is identified by its controlled setting, not by the topic being studied.

Field experiments

Another type is the field experiment.

In a field experiment, the researcher still changes the independent variable, so the study is still genuinely experimental. The difference is that the research takes place in a more natural environment, such as a school, street, store, or workplace.

Because the setting is real, behavior may be more natural than in a laboratory experiment. This can make the findings more believable as an account of what people really do. However, field experiments usually involve less control over outside influences. Noise, interruptions, and unexpected events may affect behavior, making it harder to be sure that the independent variable alone caused the result.

Field experiments can therefore offer a useful balance between experimental control and realism, but they do not provide as much control as laboratory experiments.

Natural experiments

A natural experiment is different because the researcher does not create the independent variable.

The psychologist studies the effects of a naturally occurring event or situation. This means the researcher takes advantage of circumstances that already exist. Natural experiments are often used when it would be impossible, impractical, or unethical to deliberately create the condition being studied.

A strength of the natural experiment is that it allows psychologists to investigate important real-life issues that cannot be produced on purpose. However, because the researcher has less control, it can be harder to rule out other influences. As a result, claims about cause and effect may be less secure than in laboratory experiments.

The essential identifying feature is simple: in a natural experiment, the independent variable is naturally occurring, not manipulated.

Quasi-experiments

A quasi-experiment also involves an independent variable that is not manipulated by the researcher, but it is different from a natural experiment.

In a quasi-experiment, the groups being compared already exist before the study begins. The independent variable is usually a participant characteristic or status that cannot be changed by the researcher. Because of this, the researcher measures the dependent variable across these existing groups.

Quasi-experiments are useful when psychologists want to compare people who naturally differ in an important way. They are common when the independent variable could not realistically be assigned by the researcher. However, since participants already differ from one another, other differences between the groups may also affect the outcome. This means control is lower than in laboratory or field experiments.

The main exam distinction is:

• natural experiment = the independent variable comes from a naturally occurring event or situation

• quasi-experiment = the independent variable comes from pre-existing participant differences

How to identify the type of experiment

A reliable way to classify an experiment is to ask two questions.

Decision-tree figure used in research methods to determine whether an event or condition qualifies as a natural experiment. It highlights the logic of classification—especially whether exposure is outside the researcher’s control and whether assignment is plausibly random—connecting directly to exam-style identification of experiment types. Source

First, did the researcher manipulate the independent variable?

• If yes, the study is either a laboratory experiment or a field experiment.

• If no, the study is either a natural experiment or a quasi-experiment.

Second, where does the independent variable come from?

• If it was manipulated in a controlled setting, it is a laboratory experiment.

• If it was manipulated in a real-world setting, it is a field experiment.

• If it arose from a naturally occurring event or situation, it is a natural experiment.

• If it came from pre-existing differences between participants, it is a quasi-experiment.

In exam answers, always name the type of experiment and then justify it using the correct feature. AQA rewards precise identification, especially when students clearly distinguish natural and quasi experiments.