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Table number
NATIONAL UNIVERSITY OF SINGAPORE
EXAMINATION
ST1232
STATISTICS FOR LIFE SCIENCES
(Semester 1 : AY 2011-2012)
November 2011 - Time Allowed: 2 Hours
_________________________________________________________________
INSTRUCTIONS TO CANDIDATES
1.
This examination paper contains FOUR (4) multiple-choice questions, and FOUR (4)
structured questions. The examination paper comprises FOURTEEN (14) printed pages.
2.
Candidates must answer ALL questions. For the multiple-choice questions, each correct
answer will be awarded 3 marks, whereas one mark will be deducted for each incorrect
answer. No marks will be awarded or deducted if the option (e) is selected as the answer for
any of the questions. The mark allocated for each part of the structured question is shown in
brackets. The total mark for this paper is 60.
3.
Candidates may use programmable calculators and may bring one handwritten A4-size help
sheet, written on both sides.
4.
This is a CLOSED BOOK examination.
5.
Please enter the answer to each question in the space allocated in the question sheet.
6.
Write down your matriculation number in the space below, and your table number at the top
right hand corner of the page.
Matriculation No: ___________________________
Question
1-4
5
6
7
8
Marks
scored
Max. marks
Total
12
10
8
16
14
(60)
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Questions 1-4 [12 marks]
a. Probability that the data support the null hypothesis, given the alternative hypothesis is
actually correct
b. Probability that the data support the alternative hypothesis, given the null hypothesis is
actually correct
c. Probability that the null hypothesis is actually correct, given the data support the
alternative hypothesis
d. Probability that the alternative hypothesis is actually correct, given the data support the
null hypothesis
e. I don’t know
Question 2. Which of the following statements is true?
a. The larger the sample size, the greater the standard error of the estimated parameters
b. The more categories you want to have in a nominal categorical variable, the larger the
sample size needed to draw an inference with the same precision
c. As sample size decreases, so does the size of the confidence interval for the parameter
d. Listing the individuals in Singapore by ethnic group and choosing a proportion from
within each ethnic group at random is an example of simple random sampling
e. I don’t know
Question 3. What will happen (all things remaining equal) to a confidence interval if you calculated a
99 percent confidence interval rather than a 95% confidence interval?
a. It will be narrower
b. The width will not change
c. The sample size will increase
d. None of the above
e. I don’t know
Question 4. Which of the following statements is true?
a. A Type II error is the failure to reject a false null hypothesis
b. Assuming innocence until “proven” guilty, a Type I error occurs when a truly guilty
person is found to be innocent
c. In two independent tests, if the P-value of test A is 0.001 and the P-value of test B is 0.01,
then the effect size observed in A is necessarily bigger than the effect size observed in B
d. When the P-value is < 0.05, this indicates that the null hypothesis is likely to be true
e. I don’t know
Q1 Ans:
2
Q2 Ans:
Q3 Ans:
Q4 Ans:
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Question 5. [10 marks]
Norton and Dunn carried out a case-control survey in 1985 on snoring behavior in relation to the
presence or absence of heart disease. In a summarized version of their survey, subjects were
categorized as either non-snorers or snorers, which were charted according to reports by the subjects’
spouses.
Heart Disease
No Heart Disease
Total
Snorers
86
1,019
1,105
An analysis with SPSS yielded the following output.
3
Non-snorers
24
1,355
1,379
Total
110
2,374
2,484
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Question 5. (10 marks)
On the basis of the analyses, investigate the belief that snoring is associated with heart disease onset,
stating what the appropriate null and alternative hypotheses are.
Answer to Question 5 to be written below:
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Question 6. [8 marks]
The time taken for a drug therapy to take effect in the body is often vital in deciding the best
treatment to assign for a patient in a critical condition. There are two competing drugs in the market,
and a clinical trial has been performed across two separate groups of 50 individuals to investigate the
time-to-effect for these two treatments. The data from the clinical trial measure the time taken in
minutes for each treatment to be effective. These data were subsequently analysed by a junior
statistician, who produced the following output:
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6
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Based on the output, comment on whether there is any difference in the time-to-effect for these two
treatments. (8 marks)
Answer to Question 6 to be written below:
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Question 7. [16 marks]
A study into the time taken to complete a 100 metre sprint by male and female athletes was
conducted. The data originated from 25 races which were held once every two years across a span of
50 years from 1960 to 2008.
Question 7a. (5 marks)
On the basis of the scatterplot figure above (ignoring the dashed and dotted regression lines for the
time being), comment on how the time taken to complete 100 metres has changed over the years.
Answer to Question 7a to be written below:
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Question 7b. (8 marks)
A local newspaper reporter took a look at the scatterplot and added the two regression lines (dashed
and dotted) as shown in the figure. He went on to report that from the year 2050 onwards, female
athletes are expected to complete the 100 metre sprint in a shorter time than male athletes. Comment
on the overall suitability of the regression lines and the validity of his report.
Answer to Question 7b to be written below:
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Question 7c. (3 marks)
A junior analyst with a local newspaper attempted to explain the relationship between the timespan
(year) and the time taken to complete the 100 metre sprint. Based on the scatterplot, she decided to fit
a regression model adjusting for gender, and produced the following analysis:
Parameter
Intercept
Gender-male
Year
Beta
Std. Error
P-value
69.783
-1.195
-0.029
5.207
0.076
0.003
1.1  10-17
2.0  10-20
8.7  10-17
95% Confidence Interval
Lower Bound Upper Bound
59.370
80.196
-1.346
-1.044
-0.035
-0.024
Comment on the validity of this analysis, in light of the scatterplot figure seen earlier.
Answer to Question 7c to be written below:
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Question 8. [14 marks]
A survey on the salary of 52 tenure-track professors was performed in 1972 to investigate whether
there were any evidence of discrimination. The following information is available:
Variable name
sex
rank
year
degree
years_degree
salary
Description
Coded 0 for female and 1 for male
Current professorial rank of the person, one of: Assistant,
Associate or Full Professor
Number of years in current rank
Highest degree, whether Doctorate or Masters
Number of years since the highest degree was earned
Annual salary, in dollars
A plot of the salary by gender is shown below:
Question 8a. (3 marks)
Comment on the figure above, specifically focusing on whether there is any evidence of gender
discrimination.
Answer to Question 8a to be written below:
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Question 8b. (3 marks)
A multivariate regression model is fitted to the data, and the following output is generated:
Parameter
Beta
Std. Error
P-value
Intercept
rank-associate
rank-full
year
degree-masters
years_degree
sex-male
16912
5292
11119
476
1389
-125
-1166
816
1145
1352
95
1019
77
926
1.2  10-24
3.2  10-5
1.6  10-10
8.7  10-6
0.180
0.115
0.214
95% Confidence Interval
Lower Bound Upper Bound
15280
18545
3002
7583
8415
13822
286
666
-649
3426
-280
30
-3018
685
On the basis of the analysis above, what is the evidence that male academics on average are paid
more than the female equivalent?
Answer to Question 8b to be written below:
Question 8c. (4 marks)
On the basis of the cross-tabulation table below on the distribution of academics by their rank and
gender, explain what may have explained the disparity between the figure in (a) and the output seen
in (b).
Female
Male
Assistant
8
10
Associate
2
12
Answer to Question 8c to be written below:
12
Full
4
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Question 8d. (4 marks)
An associate professor is interested to investigate whether there was any significant difference in the
salaries of associate versus the full professors. Are the analyses performed thus far adequate to
address whether there is any difference in the salary of an associate professor when compared to a full
professor of the same gender and experience? If so, comment whether there is any difference.
Answer to Question 8d to be written below:
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ST1232
ANSWER CHECKLIST
To help ensure that you have answered all the relevant questions, the boxes below remind you of the
number of parts each question has. You are welcome to tick the boxes to indicate you have completed
the relevant parts of each question. You will not be penalized for not ticking the boxes.




Question 1 (3 marks)
Question 2 (3 marks)
Question 3 (3 marks)
Question 4 (3 marks)
 Question 5 (10 marks)
 Question 6 (8 marks)
 Question 7a (5 marks)
 Question 7b (8 marks)
 Question 7c (3 marks)




Question 8a (3 marks)
Question 8b (3 marks)
Question 8c (4 marks)
Question 8d (4 marks)
~~~ END OF PAPER ~~~
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