Which of the following sampling techniques could result easily in biased statistics?
a government employee decides to wait at a bus stop to survey people about whether they support a certain candidate in an upcoming federal election.
a student council representative puts up a poster in the school that asks students whether they favor longer class periods. the students interested in answering the survey would then e-mail their answer to the student council for the data to be analyzed.
the principal of a large school assigns a number to each student in the school, places the numbers in a drum, and selects 75 numbers without replacement. he then compares these numbers with the numbered list of students and surveys these students about whether they favor a proposed new policy that requires students to wear indoor shoes only when in the school.
the owner of a small business of 300 employees draws 35 employee names out of the 300 names in a hat to survey them to determine the satisfaction level of employees with respect to healthcare benefits offered to all employees.