The experimental method: establishing causal relationships

The experimental method is considered the cornerstone of scientific research in social psychology, as it is the only approach that allows researchers to establish with a reasonable degree of certainty cause-and-effect relationships between variables.

Its design is based on the controlled manipulation of one or more factors to observe the resulting impact on others.

Manipulation of the Independent Variable

The defining characteristic of the experimental method is the deliberate and systematic manipulation of the independent variable by the researcher.

The independent variable is the factor that is hypothesized to cause a change in another variable.

To study its effect, the researcher creates different levels, or conditions, of this variable and assigns participants to each of these conditions.

For example, if a social psychologist wants to investigate whether exposure to aggressive role models (independent variable) increases aggressive behavior in children (dependent variable), they might expose one group of children to a video with aggressive content and another group to a video with neutral content.

Measuring the Dependent Variable

The dependent variable is the factor that is measured to determine whether it has been affected by the manipulation of the independent variable. It is the outcome or effect that is expected to be observed.

In the previous example, after exposure to the videos, the children's level of aggressive behavior would be measured in a subsequent play situation.

If the group exposed to the violent video consistently shows higher levels of aggression, it could be inferred that exposure to violence (independent variable) caused an increase in aggression (dependent variable).

Random Assignment and Control for Extraneous Variables

To ensure that the observed differences in the dependent variable are truly due to the manipulation of the independent variable and not due to other pre-existing differences between the participants in the groups, a crucial procedure is used: random assignment.

This means that each participant has an equal chance of being assigned to either experimental condition (for example, to the group that watches the violent video or to the one that watches the neutral video).

Random assignment helps balance individual characteristics (such as personality, intelligence, etc.) among the groups, minimizing their possible influence as confounding variables.

Furthermore, experimental control involves keeping constant all other conditions and factors that are not the independent variable,so that they do not interfere and the effect of the manipulated variable can be isolated.

Internal and External Validity in Experimentation

A well-designed experiment is characterized by high internal validity, which means that there is high confidence that the changes in the dependent variable were directly caused by the manipulation of the independent variable.

However, this high internal validity, often achieved in very controlled laboratory settings, can sometimes compromise external validity.

External validity refers to the degree to which the results of the study can be generalized to other situations, populations, and real-world contexts.

Since laboratory experiments can be artificial, it is important to consider how to replicate or complement the findings in more naturalistic settings to ensure their broader applicability.