PH 7B Public Health Statistics IIHomework 1
Question 1 (5 pts): Which of the following correlation coefficients shows the strongest
relationship?
A. 0.68
B. -0.05
C. 0.50
D. -0.96
Explain:
Question 2 (5 pts): True or False: If y is usually greater than x, the correlation coefficient
between x and y will be positive.
Ture or False:
Explain:
Question 3 (5 pts): The correlation coefficient between body weight and blood pressure for
men was about 0.70; for the women, it was about the same. If you take the average of men and
women, respectively, the correlation coefficient between body weight and blood pressure would
be___________
A. About 0.70 B. Between 0.50 – 0.70 c. Higher than 0.70
Explain:
Question 4 (5 pts):True or False: In a study of students’ GPA among students from 10 different
majors at UCI, the average GPA is 3.7 in Biological Science while the average GPA is 3.6 in
Engineering. So the data shows that on average, the instructors in Biological Science are doing
a better job in teaching than the instructors in the Engineering department.
True or False:
Explain:
PH 7B Public Health Statistics II
Homework 1
Question 5 (15 pts): The table below records the minutes of exercise per day and hours of
sleep during weekdays and weekends in a research study. (use n=7, keep one decimal place)
Participant ID
Weekdays
Weekends
Exercise
(min)
Sleep
(hours)
Exercise
(min)
Sleep
(hours)
1
40
7
65
7
2
80
9
45
8
3
75
8
75
6
4
60
7
80
9
5
45
8
50
7
6
90
7
20
9
7
55
6
35
8
1) Find out the correlation coefficient between hours spent on exercise and hours of sleep
during weekdays and weekends, respectively. Show your work.
2) On what days (weekdays or weekends), hours spent on exercise is more strongly
correlated with hours of sleep? Why?
3) The same group of participants all decided to extend 20 minutes of exercise everyday
during weekdays and double the amount of their exercise time on the weekend.
However, they found out their sleep time still remained the same. Calculate the new
correlation coefficients for both groups and explain how it differs from the previous
schedule.
PH 7B Public Health Statistics II
Homework 1
Question 6 (15pts): There was a health study among the senior population in Orange County,
where a large group of individuals have their systolic blood pressure (SBP) measured at age 65
and again at age 75. The following results are obtained.
Age 65: average SBP = 140 mmHg, SD=5 mmHg
Age 75: average SBP = 145 mmHg, SD=7.5 mmHg
r=0.80
1) Estimate the average SBP at age 75 for all the individuals who had SBP of 145 mmHg at
age 65.
2) Predict the SBP at age 75 for an individual who had SBP of 135 mmHg at age 65.
3) Another person aged 65 from New York City, with an SBP of 150 mmHg, would like to
know his systolic blood pressure in 10 years based on your research results. Would you
be able to help him calculate it? If so, write down your prediction. If not, explain why.
