College students are overrepresented in psychological research studies, according to the textbook "Research in Psychology: Methods and Design." The college population is often the most accessible one for professors conducting research, but they're not always the best population to use. Psychology researchers debating which subjects to use should carefully weigh the availability of college students against the risk of developing an unrepresentative sample.
College students are a readily available population on college campuses, where many psychological studies take place. This availability, however, may lead to a self-selection bias. If a professor asks her students if they want to participate in a study on sexuality, for example, only students who are comfortable discussing sex are more likely to participate. This can alter the data, making it hard to generalize it even to other college students.
College students are not representative of the general population. They are younger, keep different hours, have different habits and may have different values. Consequently, data gleaned from college students can't be universalized to the general population. For example, a college student may report that he does not feel anxious about how potential employers might view his social networking habits. This could be because he's not yet focused on finding a job or because social networking is such a key component of college life. If generalized to the broader population, this could lead to misconceptions about people's willingness to share information on social networking.
Using college students is generally less expensive than seeking research subjects outside of the college population. Professors can tell their students about studies, use campus listservs or post fliers on campus. If studies offer a small stipend, this might be a stronger incentive for a financially struggling college student to participate, whereas an adult professional might be unwilling to give up her entire day for a small amount of money.
If researchers are students' professors, students may already know about the research and unconsciously alter their answers to fit with their professors' theories. For example, a professor who argues in class that sports make students more aggressive, might subtly influence his students. Sports players might report higher rates of aggression and non-sports players might claim to see more aggression in sports players.
Any time human subjects are involved in research, researchers must gain informed consent. However, there are additional ethical considerations with college students. Professors who offer extra credit might recruit participants who are unwilling to give correct information or who feel coerced into the project. Confidentiality can be a challenge when the researchers are people the student knows, so professors should ensure that student privacy is protected and recruit other researchers to interview students they know well.