What does it mean if a study has high internal validity?

High internal validity indicates that a study effectively demonstrates a causal relationship between the independent and dependent variables. This means that the observed changes in the dependent variable can be confidently attributed to the manipulation of the independent variable, rather than to other extraneous factors. A study with strong internal validity has controlled for confounding variables, thus enhancing the credibility of its findings regarding the cause-and-effect relationship.

For example, if researchers want to assess the effectiveness of a new therapy on reducing anxiety, high internal validity would mean that any changes in anxiety levels in the study participants are likely due to the therapy itself, not because of other influences like participant characteristics or environmental factors.

In contrast, while random assignment and representative samples are important aspects of study design that can contribute to internal validity and external validity, they do not alone guarantee high internal validity. A representative sample may ensure broader applicability of the findings, but this does not directly confirm that the study accurately identifies the effect of the independent variable on the dependent variable. Therefore, while option B addresses the core essence of internal validity, the other options focus on other aspects of research design that may influence the overall quality and applicability of the study’s conclusions.