recruiting volunteers

What is the effect of recruiting volunteers to participate in a randomized experiment? 

The results will be more credible because people who really wanted to participate took part in the study. 

The results cannot necessarily be extended to the larger population. 

There will be no effect because the people are always randomly assigned to treatments, eliminating any type of bias. 

Researchers are never allowed to use volunteers to participate in an experiment. 

(2) What does randomization mean in terms of experiments? 

Each of the experimental units is randomly selected to participate. 

Each of the experimental units is randomly assigned to a treatment. 

The researchers randomly select which treatments they will include in the experiment. 

None of the above. 

(3) It is the purpose of what type of study to find out whether one or more explanatory variables are related to a certain disease (for example, whether smoking causes lung cancer) 

Case-control study 

Matched-pairs experiment 

Block design 

None of the above 

(4) Which of the following statements about case-control studies is false? 

Case-control studies have some clear advantages over randomized experiments. 

A properly designed case-control study does a good job of reducing potential confounding variables. 

Any controls that are selected will improve the quality of the results of the study. 

None of the above. 

(5) Suppose you are reading a newspaper article discussing the results of the latest medical study but the information is incomplete (as in many cases with the media). What should you do? 

Disregard the results because they cannot be checked out fully. Be suspicious of the results;

if some information is missing, perhaps there is a reason they do not want you to know. 

See if you can find the original source of the report or contact the authors for the missing information. 

Assume that the results are valid because they appeared in a newspaper. 

(6) Four hundred women participated in this study. Researchers found that children ages 3 and 4 whose mothers smoked 10 or more cigarettes a day during pregnancy scored about 9 points lower on intelligence tests than the children of nonsmokers. The gap narrowed to 4 points against children of nonsmokers when a wide range of interrelated factors were controlled for. The lead researcher was quoted as saying “It is comparable to the effects that moderate levels of lead exposure have on children’s IQ scores.” This was what type of study? 

Case-control design 

Observational study 

Matched-pairs experiment 

None of the above 

(7) If the bars of a histogram represent the proportion of the total count that falls into each interval, what must the heights of the bars sum to? 

The total number of numbers in the data set. 

1 divided by the total number of intervals used in the histogram. 

Not enough information to tell.

One. 

(8) Which of the following statements regarding stem plots is false? 

A stem plot allows you to retrieve the original data (assuming no digits are dropped). 

A stem plot can never reuse the same stem digit twice. 

If a certain value in your data set is repeated three times, it must appear 3 times in appropriate stem and leaf of the stem plot. 

None of the above statements are false. 

(9) Suppose that in a five-number summary you find that a larger gap exists between the extremes and the quartiles than between the quartiles and the median. What does this mean about the shape of the data set? 

The data are clumped at the high and low ends. 

The data are not symmetric. 

Not enough information to tell. 

The data are clumped in the middle 

(10) Which of the following does not require the data to be ordered before you can get the right answer? 

Mean 

Median 

Quartiles 

Range 

(11) If the width of a box in a box plot is very large, compared to the rest of the box plot, what does that mean about the shape of the data set? 

The data are very spread out in the middle. 

The data are clumped tightly in the middle. 

The data are not symmetric. 

Not enough information to tell. 

(12) Which of the following cannot be obtained from a box plot? 

Mean 

Median 

IQR 

Range

(13) What is the relationship between the variance and the standard deviation? 

The variance is the square root of the standard deviation. 

The variance is twice the standard deviation. 

There is no relationship between them. 

The variance is the square of the standard deviation. 

(14) Suppose a data set is skewed left. What is the most likely relationship between the mean and the median? 

The mean is larger than the median. 

The mean and the median are not related to each other at all. 

The mean is smaller than the median. 

The mean and the median are equal