Question

a chemist at a pharmaceutical company wants to test the quality of a new batch of microscopes. which of the following best describes a systematic sample of microscopes?
(a)
the chemist forms 4 groups of microscopes based on the prices of the microscopes. then, he selects 16 microscopes at random from each group.
the chemist assigns a different random number to each microscope. using a random number table, he draws 64 of those numbers at random. then, he selects the 64 microscopes assigned to the drawn numbers. every set of 64 microscopes is equally likely to be drawn using the random number table.
the chemist takes a list of the microscopes and selects every 4th microscope until 64 microscopes are selected.
(b)
counselors at a college want to poll students about how much time the students spend studying. which of the following best describes a convenience sample of students?
the counselors take a list of the students and select every 5th student until 90 students are selected.
the counselors select the 90 students living in a particular dorm building on campus as easily accessible. so, the counselors select the 90 students living in that particular dorm building on campus as easily accessible.
the counselors use a computer program to draw 90 students at random and select these students. every set of 90 students is equally likely to be drawn by the computer program.
(c)
the organizers of a conference want to survey attendees about the registration fee. which of the following best describes a stratified sample of attendees?
the organizers form 7 groups of attendees based on the attendees employment statuses. then, the organizers select 8 attendees at random from each group.
the organizers form 8 groups of attendees based on the day the attendees registered. then, the organizers randomly choose 7 groups and select all of the attendees in these groups.
the organizers select the first 56 attendees who register for the conference because these attendees are easily accessible.

Explanation:

• (a): The chemist divides the microscopes into 4 groups based on price (strata) and then selects 16 at random from each group. This is stratified sampling as it involves dividing the population into subgroups (strata) and sampling from each.
• (b): The counselors take every 5th student until 90 are selected. This is systematic sampling where elements are selected at regular intervals.
• (c): The organizers first divide attendees into 7 groups based on employment status (strata) and then select 8 at random from each group. This is stratified sampling as it uses subgroups (strata) and random sampling within each.

Answer:

(a) stratified sample; (b) systematic; (c) stratified sample.