Merit pay is a system by which employees are paid based on their performance. Although this system generally causes workers to do a better job, it is often opposed by these employees, since if forces them to work harder. For example, this is consistently opposed by teachers' unions in favor of seniority and advanced degrees, although "we know from a wide and rarely disputed body of research that years of experience and degrees obtained are simply unrelated to a teacher's effectiveness in the classroom."[1]