Describe the selection bias likely to exist in the following situations:
a. A study of 5,000 office workers in Chicago found that those who ate fast food for lunch three or more times per week were 30 percent more likely to suffer from heart disease than those who brought their lunch to work three or more times per seek. Therefore, eating fast food three or more times per week leads to a higher incidence of heart disease in office workers.
b. A survey of senior assisted-living facilities found that 80 percent of residents are female. Therefore, as they age, men tend to need less assistance with day-to-day living than do women.
c. A study of 1,000 college graduates found that students graduating from a prestigious private university earned, on average, $40,000 more annually than students graduating from a typical public university. Therefore, an education from a prestigious private university will enhance a student’s earnings.