Question

"Ecstasy" was a popular drug in the 1990s. It produced a sense of euphoria derisively called the "yuppie high." One investigator made a careful sample survey to estimate the prevalence of drug use at Stanford University. Two assistants were stationed on the main campus plaza and instructed to interview all students who passed through at specified times. As it turned out, 39% of 369 students interviewed said they had used Ecstasy at least once. Does the investigator’s procedure give a probability sample of Stanford students? Answer yes or no, and explain.

Answer 1

No, the investigator's methods used at Stanford University do not provide a probability sample because it only includes a subset of students based on their use of the main plaza at certain times, leading to sampling bias and an unreliable estimate of Ecstasy use prevalence.

Step-by-step explanation:

The investigator's procedure does not give a probability sample of Stanford students. A probability sample would require each member of the population to have a known and non-zero chance of being included in the sample. However, this method of sampling, with assistants interviewing students who pass through a specific location at specified times, is subject to sampling bias. Students who use the main plaza at those times are not representative of all Stanford students; for instance, off-campus students, students with schedules that don't take them to the plaza, or students studying abroad may be excluded. The sampling method, therefore, does not provide a reliable prevalence estimate of Ecstasy use at Stanford University.

Answer 2

Yes

Step-by-step explanation:

According to the Central Limit Theorem, the sample size, being n larger than 30, is representative of the Standford students´ use of the drug, in this case, being ecstasy. Another reason why the procedure works is the random sampling, where the assistants made sure that the only characteristic that mattered was being a student; gender, major being pursued, age, etc. were not of relevance.