Biostatistics

62 CHAPTER 2 DESCRIPTIVE STATISTICS
72.0 97.5 130.0 68.1 86.4 70.0 73.0
59.7 89.6 76.9 74.6 67.7 91.9 55.0
90.9 70.5 88.2 70.5 74.0 55.5 80.0
76.9 78.1 63.4 58.8 92.3 100.0 84.0
71.4 84.6 123.7 93.7 76.9 79.6
45.6 92.5 65.6 61.3 64.5 72.7
77.5 76.9 80.2 76.9 88.7 78.1
60.6 59.0 84.7 78.2 72.4 68.3
67.5 76.9 82.6 85.4 65.7 65.9
Source: Data provided courtesy of Dr. N. Thilothammal.
(a) For these data compute the following descriptive measures: mean, median, mode, variance,
standard deviation, range, first quartile, third quartile, and IQR.
(b) Construct the following graphs for the data: histogram, frequency polygon, stem-and-leaf plot,
and boxplot.
(c) Discuss the data in terms of variability. Compare the IQR with the range. What does the
comparison tell you about the variability of the observations?
(d) What proportion of the measurements are within one standard deviation of the mean? Two
standard deviations of the mean? Three standard deviations of the mean?
(e) What proportion of the measurements are less than 100?
(f) What proportion of the measurements are less than 50?
Exer cises for Use wit h Large Data Set s Availabl e on th e Foll owing Websit e: www .wiley.com /
c ollege/da niel
1. Refer to the dataset NCBIRTH800. The North Carolina State Center for Health Statistics and
Howard W. Odum Institute for Research in Social Science at the University of North Carolina at
Chapel Hill (A-20) make publicly available birth and infant death data for all children born in the
state of North Carolina. These data can be accessed at www.irss.unc.edu/ncvital/bfd1down.html.
Records on birth data go back to 1968. This comprehensive data set for the births in 2001 contains
120,300 records. The data represents a random sample of 800 of those births and selected variables.
The variables are as follows:
Variable Label
PLURALITY
SEX
MAGE
WEEKS
MARITAL
RACEMOM
HISPMOM
GAINED
SMOKE
Description
Number of children born of the pregnancy
Sex of child ð1 ¼ male; 2 ¼ femaleÞ
Age of mother (years)
Completed weeks of gestation (weeks)
Marital status ð1 ¼ married; 2 ¼ not marriedÞ
Race of mother (0 ¼ other non-White, 1 ¼ White; 2 ¼ Black; 3 ¼ American
Indian, 4 ¼ Chinese; 5 ¼ Japanese; 6 ¼ Hawaiian; 7 ¼ Filipino; 8 ¼ Other
Asian or Pacific Islander)
Mother of Hispanic origin (C ¼ Cuban; M ¼ Mexican; N ¼ Non-Hispanic,
O ¼ other and unknown Hispanic, P ¼ Puerto Rican, S ¼ Central=South
American, U ¼ not classifiable)
Weight gained during pregnancy (pounds)
0 ¼ mother did not smoke during pregnancy
1 ¼ mother did smoke during pregnancy