Question
Data were collected in 20 cities on the percentage of women in the workforce. Data were collected in 1990 and again in 1994. Gains, or losses, in this
percentage were the measurement upon which the study’s, conclusions were to
be based. What kind of design was this?
I. A matched-pairs design
II. An observational study
III. An experiment using a block design
(a) I only
(b) II only
(c) III only
(d) I and III only
(e) I and II only
▶️Answer/Explanation
Ans: The correct answer is (e).
The data are paired because there are two measurements for each city, so the data are not independent. There is no treatment being applied, so this is an observational study. Matched pairs is one type of block design, but this is NOT an experiment, so III is false.
Question
You want to do a survey of members of the senior class at your school and want to select a simple random sample. You intend to include 40 students in your sample. Which of the following approaches will generate a simple random sample?
(a) Write the name of each student in the senior class on a slip of paper and put the papers in a container. Then randomly select 40 slips of paper from the container.
(b) Assuming that students are randomly assigned to classes, select two classes at random and include those students in your sample.
(c) From a list of all seniors, select one of the first 10 names at random. The select every nth name on the list until you have 40 people selected.
(d) Select the first 40 seniors to pass through the cafeteria door at lunch.
(e) Randomly select 10 students from each of the four senior calculus classes.
▶️Answer/Explanation
Ans:The answer is (a).
In order for this to be an SRS, all samples of size 40 must be equally likely. None of the other choices does this [and choice (d) isn’t even random]. Note that (a), (b), and (c) are probability samples.
Question
Which of the following is (are) important in designing an experiment?
I. Control of all variables that might have an influence on the response variable
II. Randomization of subjects to treatment groups
III. Use of a large number of subjects to control for small-sample variability
(a) I only
(b) I and II only
(c) II and III only
(d) I, II, and III
(e) II only
▶️Answer/Explanation
Ans:The correct answer is (d).
These three items represent the three essential parts of an experiment: control, randomization, and replication.
Question
Your company has developed a new treatment for acne. You think men and women might react differently to the medication, so you separate them into two groups. Then the men are randomly assigned to two groups and the women are randomly assigned to two groups. One of the two groups is given the medication and the other is given a placebo. The basic design of this study is
(a) completely randomized
(b) blocked by gender
(c) completely randomized, blocked by gender
(d) randomized, blocked by gender and type of medication
(e) a matched-pairs design
▶️Answer/Explanation
Ans:The correct answer is (b).
You block men and women into different groups because you are concerned that differential reactions to the medication may confound the results. It is not completely randomized because it is blocked.
Question
A double-blind design is important in an experiment because
(a) There is a natural tendency for subjects in an experiment to want to please the researcher.
(b) It helps control for the placebo effect.
(c) Evaluators of the responses in a study can influence the outcomes if they know which subjects are in the treatment group and which are in the control group.
(d) Subjects in a study might react differently if they knew they were receiving an active treatment or a placebo.
(e) All of the above are reasons why an experiment should be double-blind.
▶️Answer/Explanation
Ans:The correct answer is (e).