Chapter 5 Answer Key
Essentials of Biostatistics for Public Health, 2 Edition
nd
Lisa M. Sullivan, PhD
Chapter 5 Solutions to Problems
1. A recent study reported that the prevalence of hyperlipidemia (defined as total cholesterol
over 200) is 30% in children 2-6 years of age. If 12 children are analyzed,
a. What is the probability that at least 3 are hyperlipidemic?
P(X > 3) = 1 – P(X < 3) = 1 – {P(X=0) + P(X=1) + P(X=2)}
P(X = 0) =
12 !
0!(12−0)!
0 . 30(1−0.3)12 0−=
0.0138
P(X = 1) =
12 !
1!(12 −1)!
0 . 31(1−0.3)12−1=
0.0712
P(X = 2) =
12 !
2!(12 −2)!
0 . 32(1−0 .3 )12 2−=
0.1678
= 1- {0.0138 + 0.0712 + 0.1678) =1- 0.2528 = 0.7472.
b. What is the probability that 3 are hyperlipidemic?
P(X=3) =
12 !
3 3!(12− )!
0 .33(1−0 . 3 )12−3=
0.2397.
c. How many would be expected to meet the criteria for hyperlipidemia?
=np=12(0.3) = 3.6
2. Hyperlipidemia in children has been hypothesized to be related to high cholesterol in their
parents. The following data were collected on parents and children.
CHILD Both Parents
Hyperlipidemic
One Parent
Hyperlipidemic
Neither Parent
Hyperlipidemic
Not Hyperlipidemic 13 34 83
Hyperlipidemic 45 42 6
a. What is the probability that one or both parents are hyperlipidemic?
P(one or both parents are hyperlipidemic) = (58+76)/223 = 134/223 = 0.600.
© 2012 Jones & Bartlett Learning, LLC 1
Chapter 5 Answer Key
Essentials of Biostatistics for Public Health, 2 Edition
nd
Lisa M. Sullivan, PhD
b. What is the probability that the child and both parents are hyperlipidemic?
P(child and both parents are hyperlipidemic) = 45/223 = 0.202.
c. What is the probability that a child is hyperlipidemic IF neither of his/her parents are
hyperlipidemic?
P(child is hyperlipidemic | neither parent is hyperlipidemic) = 6/89 = 0.067.
d. What is the probability that a child is hyperlipidemic IF both of his/her parents are
hyperlipidemic?
P(child is hyperlipidemic | both parents are hyperlipidemic) = 45/58 = 0.776.
3. Total cholesterol in children aged 10-15 is assumed to follow a normal distribution with a
mean of 191 and a standard deviation of 22.4.
