An employer offers its employees a program that will provide up to four free psychological counseling sessions per calendar year. To evaluate satisfaction with this service, the counseling office mails questionnaires to every 10th employee who used the benefit in the prior year. There were 1000 employees who used the benefit. Therefore, 100 surveys were sent out. However, only 25 of the potential respondents completed and returned their questionnaire.
a) Describe the population for the study.
b) Describe the sample.
c) What concern is raised by the fact that only 25 of the 100 questionnaires were completed and returned?