Statistical Methods for Psychology

Exercises 59

2.25 Rogers and Prentice-Dunn (1981) had subjects deliver shock to their fellow subjects as part
of a biofeedback study. They recorded the amount of shock that the subjects delivered to
white participants and black participants when the subjects had and had not been insulted
by the experimenter. Their results are shown in the accompanying figure. Interpret these
results.

2.26 The following data represent U.S. college enrollments by census categories as measured in
1982 and 1991. Plot the data in a form that represents the changing ethnic distribution of
college students in the United States. (The data entries are in thousands.)

Ethnic Group 1982 1991

White 9,997 10,990

Black 1,101 1,335

Native American 88 114

Hispanic 519 867

Asian 351 637

Foreign 331 416

2.27 The following data represent the number of AIDS cases in the United States among people
aged 13–29 for the years 1981 to 1990. Plot these data to show the trend over time. (The
data are in thousands of cases and come from two different data sources.)

Year Cases

1981–1982 196

1983 457

1984 960

1985 1685

1986 2815

1987 4385

1988 6383

1989 6780

1990 5483

(Before becoming complacent that the incidence of AIDS/HIV is now falling in the U.S.,

you need to know that in 2006 the United Nations estimated that 39.5 millionpeople were

living with AIDS/HIV. Just a little editorial comment.)

2.28 More recent data on AIDS/HIV world-wide can be found at http://data.unaids.org/
pub/EpiReport/2006/2006_EpiUpdate_en.pdf. How does the change in U.S. incidence rates
compare to rates in the rest of the world?

No insult Insult

Shock level

160

150

140

130

120

110

100

90

80

70

Black

White

60