What is essential to increase internal validity in an experiment?

To increase internal validity in an experiment, it is crucial to ensure that only the independent variable changes while all other variables remain constant. Internal validity refers to the degree to which a study accurately establishes a causal relationship between the independent and dependent variables. If there are extraneous variables that change alongside the independent variable, it becomes difficult to determine whether the observed effects are truly due to manipulation of the independent variable or if they might be influenced by other factors.

By controlling for other variables and only allowing the independent variable to vary, researchers can confidently attribute any changes in the dependent variable directly to the manipulation of the independent variable. This control and isolation of variables is fundamental to the experimental design, enhancing the reliability of the conclusions drawn from the study.

In contrast, reducing the number of participants might lead to lower statistical power and increased risk of chance findings, which does not support internal validity. While a diverse participant pool can enhance external validity (the extent to which findings can be generalized), it does not inherently strengthen internal validity. Similarly, qualitative research methods often focus on depth rather than manipulation and control of variables, which are key for establishing causation.