The article "Workers Grow More Dissatisfied" in the San Luis Obispo Tribune (August 22, 2002) states that "a survey of 5000 people found that while most Americans continue to find their jobs interesting, and are even satisfied with their commutes, a bare majority like their jobs." This statement was based on the fact that only 51 percent of those responding to a mail survey indicated that they were satisfied with their jobs. Describe any potential sources of bias that might limit the researcher's ability to draw conclusions about working Americans based on the data collected in this survey.