Experimental Method

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The Experimental Method

Experiments are one of the most popular and useful research methods in psychology. The key types are laboratory and field experiments.

Role in psychology

Experiments play a major role throughout psychology.
As a method, experiments allow one variable to be manipulated while keeping everything the same.
This allows researchers to show cause and effect.

Laboratory experiments

Some experiments take place under controlled condition, such as in a university room supervised by the researchers.
These are called laboratory (or ‘lab’) experiments.
The advantage of laboratory experiments is that they increase the level of control that a researcher can have.
But they reduce the level of ecological validity of the research.

Field experiments

Other experiments take place in a participant’s natural surroundings, such as their school or workplace.
These are called field experiments.
The advantage of field experiments is that they increase the ecological validity of the study by making the surroundings more realistic.
But they reduce the level of control.

True experiments

Both field experiments and lab experiments control the variables under investigation, and randomly allocate participants to groups.
These characteristics mean that they are true experiments.

Quasi-Experiments

Quasi-experiments are not true experiments because they lack control over the experimental groups used.

Lack of random allocation

Sometimes it is not possible for an experimenter to randomly allocate participants to experimental groups.
- For example, if one of the variables under investigation is gender, people can’t be randomly allocated to ‘male’ and ‘female’ conditions.
A study is termed a quasi-experiment if it lacks random allocation to groups but is like a true experiment in most or all other ways.

Examples of quasi-experiments

Other examples of quasi-experiments include studies which compare different types of personality (e.g. introverts versus extroverts) or compare people who have a psychological disorder with a control group who do not.
Such studies cannot randomly allocate people to groups.

Quasi vs lab

Quasi-experiments could take place in a lab, and all other aspects of the research and data gathering can be controlled.
This means they are easy to mix up with laboratory experiments.

Natural Experiments

Natural experiments are logically similar to true experiments, but the situation happens by itself and so is completely uncontrolled by the researcher.

Ethics

Sometimes, for ethical or practical reasons, it is not possible for an experimenter to control and manipulate one of the variables under investigation.
- For example, it wouldn’t be ethically correct to expose people to a lot of stress to investigate its effects.
In such situations, a researcher may use a natural experiment.

Similarity to true experiments

Natural experiments are logically similar to true experiments in the sense that a variable happens, and the researcher tries to measure its effects.
- For example, they could compare the educational outcomes of school pupils who experience a lot of stress versus those who do not.

Differences to true experiments

In contrast to a true experiment or a quasi-experiment, the variable under investigation happens by itself and so is completely uncontrolled by the researcher.
The researcher also has no control at all over who is in each ‘experimental’ group.

Location of natural experiments

Because natural experiments are not set up by the researcher, they always take place in participants’ everyday surroundings such as their home or school.
This means they are easy to mix up with field experiments.