Which of the following is NOT a threat to internal validity?

Sampling error refers to the discrepancy that can occur when a sample does not accurately reflect the population from which it is drawn. This concept is primarily associated with the external validity of a study, as it can influence how well the results generalize to a broader population. Internal validity, on the other hand, focuses on the extent to which a study can establish a cause-and-effect relationship between the treatment and the outcome without being confounded by other variables.

Threats to internal validity include factors that can systematically alter the results of an experiment, such as history, which involves external events that can influence outcomes over time; selection bias, which occurs when the participants selected for the study are not representative of the broader population; and maturation, where natural changes in participants over time can affect the results. Each of these factors can directly impact the conclusions drawn from the study by introducing alternative explanations for the outcome.

In contrast, sampling error does not threaten the internal validity of a study because it does not arise from the experimental design itself or from changes occurring within the study's timeframe. Instead, it pertains to the representativeness of the sample, making it relevant to external validity. Understanding these distinctions is essential for evaluating the robustness of research findings.