The 2013 National Study of Substance Use Habits of College Student-Athletes surveyed student-athletes at NCAA member colleges and universities. The passage below is from the survey website (ncaa.org/about/resources/research/about-survey, retrieved February 13, 2018). All NCAA member institutions are asked to participate. The sampling plan achieves an appropriate representation of all NCAA student-athletes while minimizing burden to institutions by asking that all student-athletes on no more than three teams be surveyed on any campus. The teams surveyed are determined by a computer-generated random draw. The survey is administered to the selected teams in a classroom setting, and no identifying information about the athletes or the college is collected. The web site also states It is important to note that even with measures to ensure anonymity, self-reported data of this kind can be problematic due to the sensitive nature of the issues. Therefore, absolute levels of use might be underestimated in a study such as this. 

a. Was this sample a simple random sample, a stratified sample, a cluster sample, a systematic sample, or a convenience sample? Explain. 

b. Give two reasons why an estimate of the proportion of students who reported using illegal drugs based on data from this survey should not be generalized to all U.S. college students.