Everyone has theories about what causes behaviour. In order to systematically test theories, psychologists conduct research. The research methods available include experiments, questionnaires, interviews, observations, and methods using correlations. Ethical issues arise when there is a conflict between the rights and dignity of participants and the goals and outcomes of research. On the one hand they want to use their research skills to advance our knowledge and understanding of humanity, but on the other hand they have a responsibility to the people who are willing to take part in their research. Preventing psychologists from undertaking any research that might involve stress or conflict would necessarily result in a somewhat "lopsided" view of psychology. External validity refers to the validity of a study outside the research situation itself. Validity refers to whether a technique can achieve the purpose for which it was designed. Internal validity refers to the validity of an experiment within the confines in which it is carried out.