It is common practice to pay research participants. In fact, offering payments to research participants in scientific research is long-standing. Are their ethical considerations and confounding variables of research participants being paid? This could be similar to volunteering for a research study as a course requirement in colleagues or participating in a survey. Could participants who receive payments or class credit be considered confounding variables? Could payments affect the motivation of participation and affect responses, which are critical in the interpretation of any study results? What about participant bias? what about subject recruitment bias?