What does internal validity measure in an experiment?

Internal validity specifically measures the extent to which a study can establish a cause-and-effect relationship between variables. It assesses whether the results of an experiment are truly due to the manipulation of the independent variable and not influenced by other confounding factors. In other words, high internal validity means that the study design effectively rules out alternative explanations for the observed outcomes, therefore strengthening the causal conclusions drawn from the research.

This concept is critical in experimental research, where establishing a direct link between an intervention (the independent variable) and an outcome (the dependent variable) is the primary goal. When researchers control for extraneous variables and use appropriate experimental designs, they enhance the internal validity, reinforcing the credibility of their causal claims.

In comparison to the other options, generalizability concerns external validity, reliability is connected to measurement consistency, and bias relates more to the systematic flaws within the study's design rather than its ability to support causal conclusions. Thus, the focus on causal relationships aligns closely with the definition and importance of internal validity in the context of experimental research.