What is the least likely reason for dropping highly anxious participants from a research study?

Dropping highly anxious participants from a research study due to ethical committees restricting research with psychological disorders is the least likely reason. Ethical review boards primarily aim to protect the welfare of participants and ensure that the research does not cause undue harm. They often encourage the inclusion of individuals with psychological disorders to better understand treatment outcomes and the effects of interventions.

The focus of ethical committees is less about excluding participants with anxiety per se and more about ensuring that the research is conducted in a manner that is sensitive to their needs and potential vulnerabilities. This means that rather than outright exclusion, researchers are encouraged to implement measures to protect the participants, such as using informed consent and providing support.

In contrast, other options point to methodological concerns that could justify excluding highly anxious individuals from a study. For example, avoiding confounding variables is crucial for maintaining the integrity of the research findings, and grouping all anxious participants together could skew results. Similarly, ensuring that the sample represents the broader population can enhance the generalizability of the study findings. Additionally, excluding participants who may lead to false rejections of the hypothesis can help ensure that the study's results are valid and reliable.