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Chapter 1
1.8 Indicate whether each of the following studies is an experiment or an observational study. If it is an experiment, identify the independent vari-able and note any possible confounding variables.
(a) A psychologist uses chimpanzees to test the notion that more crowded living conditions trigger aggressive behavior. Chimps are placed, accord-ing to an impartial assignment rule, in cages with either one, several, or many other chimps. Subsequently, during a standard observation period, each chimp is assigned a score based on its aggressive behavior toward a chimplike stuffed doll.
(b) An investigator wishes to test whether, when compared with recognized, professional scientists, recognized, professional artists tend to be born under different astrological signs.
(c) To determine whether there is a relationship between the sexual codes of primitive tribes and their behavior toward neighboring tribes, an anthro-pologist consults available records, classifying each tribe on the basis of its sexual codes (permissive or repressive) and its behavior toward neigh-boring tribes (friendly or hostile).
(d) In a study of group problem solving, an investigator assigns college stu-dents to groups of two, three, or four students and measures the amount of time required by each group to solve a complex puzzle.
(e) A school psychologist wishes to determine whether reading comprehension scores are related to the number of months of formal education, as reported on school transcripts, for a group of 12-year-old migrant children. Copyright © 2015 John Wiley & Sons, Inc.
(f) To determine whether Graduate Record Exam (GRE) scores can be increased by cramming, an investigator allows college students to choose to participate in either a GRE test-taking workshop or a control (non-test-taking) workshop and then compares the GRE scores earned subsequently by the two groups of students.
(g) A social scientist wishes to determine whether there is a relationship between the attractiveness scores (on a 100-point scale) assigned to col-lege students by a panel of peers and their scores on a paper-and-pencil test of anxiety.
(h) A political scientist wishes to determine whether males and females differ with respect to their attitudes toward defense spending by the federal gov-ernment. She asks each person if he or she thinks that the current level of defense spending should be increased, remain the same, or be decreased.
1.9 Recent studies, as summarized, for example, in E. Mortensen et al. (2002). The association between duration of breastfeeding and adult intelligence. Journal of the American Medical Ass o ciation , 287 , 2365–2371, suggest that breast-feeding of infants may increase their subsequent cognitive ((IQ) development. Both experiments and observational studies are cited.
(a ) What determines whether some of these studies are experiments?
(b) Name at least two potential confounding variables controlled by breast-feeding experiments.
Chapter 2
2.14
(a) Construct a frequency distribution for the number of difference residences occupied by graduating seniors during their college career, namely 1, 4, 2, 3, 3, 1, 6, 7, 4, 3, 3, 9, 2, 4, 2, 2, 3, 2, 3, 4, 4, 2, 3, 3, 5
(b) What is the shape of this distribution?
*2.17 Are there any conspicuous differences between the two distributions in the following table (one refl ecting the ages of all residents of a small town and the other refl ecting the ages of all U.S. residents)?
(a) To help make the desired comparison, convert the frequencies ( f ) for the small town to percentages.
(b) Describe any seemingly conspicuous differences between the two distri-butions.
NOTE: The top class (65–above) has no upper boundary. Although less preferred, as discussed previously, this type of open-ended class is employed as a space-saving device when, as in the Statistical Abstract of the United States, many different tables must be listed. Source: 2012 Statistical Abstract of the United States.
Source: 2012 Statistical Abstract of the United States. Copyright © 2015 John Wiley & Sons, Inc.
REVIEW QUESTIONS 55 (c) Using just one graph, construct frequency polygons for the two relative frequency distributions. NOTE: When segmenting the horizontal axis, assign the same width to the open-ended interval (65–above) as to any other class interval. (This tactic causes some distortion at the upper end of the histogram, since one class interval is doing the work of several. Nothing is free, including the convenience of open-ended intervals.) Answers on Page 501.
2.18 The following table shows distributions of bachelor’s degrees earned in 2005–2006 for selected fi elds of study by all male graduates and by all female graduates. (a) How many female psychology majors graduated in 2005–2006? (b) Since the total numbers of male and female graduates are fairly different— 504,600 and 676,000—it is helpful to convert fi rst to relative frequencies before making comparisons between male and female graduates. Then, inspect these relative frequencies and note what appear to be the most conspicuous differences between male and female graduates. (c) Would it be meaningful to cumulate the frequencies in either of these frequency distributions? (d) Using just one graph, construct bar graphs for all male graduates and for all female graduates. Hint: Alternate shaded and unshaded bars for males and females, respectively.
3.13 Garrison Keillor, host of the radio program A Prairie Home Companion , concludes each
Source: 2007 Digest of Educational Statistics at http://nces.ed.gov.Copyright © 2015 John Wiley & Sons, Inc. 56
*2.19 Being slightly more complex than previous tables, the following table shows both frequency distributions and relative frequency distributions of race/Hispanic origin for the U.S. population in 1980 and in 2009. It also shows the frequency (f) change and the percent (%) change of race/Hispanic origin between 1980 and 2009.
(a) Which group changed the most in terms of actual number of people?
(b) Relative to its size in 1980, which group increased most?
(c) Relative to its size in 1980, which group increased less rapidly than the general population?
(d) What is the most striking trend in these data?
Chapter 3
3.13 Garrison Keillor, host of the radio program A Prairie Home Companion , concludes each story about his mythical hometown with “That’s the news from Lake Wobegon, where all the women are strong, all the men are good-looking, and all the children are above average.” In what type of distribution, if any, would
(a) more than half of the children be above average?
(b) more than half of the children be below average?
(c) about equal numbers of children be above and below average?
(d) all the children be above average?
3.14 The mean serves as the balance point for any distribution because the sum of all scores, expressed as positive and negative distances from the mean, always equals zero. (a) Show that the mean possesses this property for the following set of scores: 3, 6, 2, 0, 4. (b) Satisfy yourself that the mean identifi es the only point that possesses this property. More specifi cally, select some other number, preferably a whole number (for convenience), and then fi nd the sum of all scores in Part (a) expressed as positive or negative distances from the newly selected number. This sum should not equal zero.
3.18 Given that the mean equals 5, what must be the value of the one missing observation from each of the following sets of observations?
(a) 1, 2, 10
(b) 2, 4, 1, 5, 7, 7
(c) 6, 9, 2, 7, 1, 2
3.19 Indicate whether the following terms or symbols are associated with the population mean, the sample mean, or both means.
(a) N
(b) varies
(c) ∑
(d) n
(e) constant
(f) subset
Chapter 4
*4. 9 For each of the following pairs of distributions, fi rst decide whether their standard deviations are about the same or different. If their standard devi-ations are different, indicate which distribution should have the larger standard deviation. Hint: The distribution with the more dissimilar set of scores or individuals should produce the larger standard deviation regard-less of whether, on average, scores or individuals in one distribution differ from those in the other distribution.
(a) SAT scores for all graduating high school seniors (a 1) or all college fresh-men
(a )
(b²) Ages of patients in a community hospital
(b 1 ) or a children’s hospital
(b²)
(c) Motor skill reaction times of professional baseball players
(c 1 ) or college students
(c ) (d) GPAs of students at some university as revealed by a random sample (d 1) or a census of the entire student body
(d ) (e) Anxiety scores (on a scale from 0 to 50) of a random sample of college students taken from the senior class (e 1) or those who plan to attend an anxiety-reduction clinic (
e 2 ) (f) Annual incomes of recent college graduates (f 1 ) or of 20-year alumni (f 2 )
4.14 (a) Using the computation formula for the sample sum of squares, verify that the sample standard deviation, s , equals 23.33 lbs for the distribution of 53 weights in Table 1.1. (b) Verify that a majority of all weights fall within one standard deviation of the mean (169.51) and that a small minority of all weights deviate more than two standard deviations from the mean.
- 17 Why can’t the value of the standard deviation ever be negative?
4.19 Referring to Review Question 2.18 on page 55, would you describe the distribution of majors for all male graduates as having maximum, interme-diate, or minimum variability?
