Biostatistics for Public Health (TM5516) - Assignment 1

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Biostatistics for Public Health (TM5516)
ASSIGNMENT 1

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Answer 1:
Table 1: Cumulative distribution of males and females in elderly community
Age group
(y)
Male
s
Female
s
Cum.
Male
Cum.
Female
Cum.
Total
65-69 8 11 8 11 19
70-74 11 15 19 26 45
75-79 7 16 26 42 68
80-84 8 13 34 55 89
85+ 3 8 37 63 100
All the people in the sample are aged greater or equal to 65 years. Total sample size ,
out of which 37 males and 63 females are present.
So, number of people aged above 65 = 100, and number of people aged over 80 = (100 – 68)
= 32.
Let X = Number of people aged above 65, and Y = Number of people aged over 80.

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Now, , and
Also, (as Y is a subset of X).
Required conditional probability,
Hence, there is 32% chance that a person over 65 years is also aged over 80 years.
Answer 2:
Let X = Aortic diameter expansion measurement (DOE)
Now,
a) The probability that DOE measurement is between 1.3 and 2.4 is evaluated as follows.
Where, is the Standard Normal Variate (S.N.V).
Now, (As normal distribution is symmetric
about Z = 0).

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= 0.86 - 0.61 = 0.25 (from standard normal table).
Hence, approximately 25% population has a DOE measurement between the
specified limits.
b) Percentage of people having no risk of AAA = 10.38%.
Hence, probability of people having no risk of AAA = 0.1038
Let X = A be the cut-off point of DOE score.
Therefore,
Now,
As normal distribution is symmetric about Z = 0.
So,
Therefore,
So, A= 1.06 is the approximate cut-off point of DOE score.