LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034
B.Sc. DEGREE EXAMINATION – PLANT BIOLOGY & BIOTECHNOLOGY

THIRD SEMESTER – April 2009
ST 3203 / 3201 – BIOSTATISTICS
Date & Time: 16/04/2009 / 1:00 – 4:00 Dept. No. Max. : 100 Marks
SECTION A
Answer all questions. (10 x 2 = 20)
 What is meant by quantitative and qualitative data?
 Mention any two properties of arithmetic mean.
 Define: Independent events.
 Let A, B and C be three mutually exclusive and exhaustive events with P(A) = P(B) / 2 , P(B) = 3 P(C) . Find P(A), P(B) and P(C).
 What is the probability of obtaining three heads in a toss of four unbiased coins?
 Let X be a random variable with the following probability distribution
X: 1 0 1 2
P[X=x]: 0.3 0.2 0.2 0.3
Find the distribution of Y = X^{2}.
 Mention any two uses of tdistribution.
 Define the term ‘Statistic’.
 Interpret the following confidence interval:
Pr(1.2 < μ < 2.7) = 0.99
 What are Type 1 error and Type II error?
SECTION B
Answer any five questions. (5 x 8 = 40)
 Calculate mean, median and mode for the following data
Weight: 5055 5560 6065 6570 7075 7580
No. of patients: 10 8 14 9 5 2
 Explain the concept of correlation and regression with an example each.
 Let X be a normally distributed random variable with mean 57 and variance 20. Find a) P(X>62)
 b) P(42<X<50)
 c) P(X< 70)
 Explain the various steps involved in hypothesis testing.
 The following data gives the age of 10 randomly chosen patients admitted in the intensive care unit of a hospital in a given week.
40, 52, 48, 63, 37, 24, 49, 58, 69, 75.
Can it be concluded, based on the above information, that the mean age of
all the patients admitted in the given week is more than 55? Test at 5 % level.
 Of the 215 subjects who were black, 58 had diabetes mellitus. Of the 1140 white subjects, 217 had diabetes mellitus. Construct a 90 % confidence interval for the difference between the two population proportions. What are the relevant population proportions?
 Explain the Mann – Whitney test to test the equality of median of two populations.
 Fit a binomial distribution to the following frequency distribution.
X: 0 1 2 3 4
f: 12 15 18 14 10
SECTION C
Answer any two questions. (2 x 20 = 40)
 a.) Draw a Box – Plot and examine the Skewness of the following
frequency distribution:
No. of children per family: 0 1 2 3 4 5 6 No. of families: 7 10 16 25 18 11 8
b.) The following data gives the Blood Pressure (Y) and age (X) of 10
patients:
Y: 78 64 89 94 88 72 90 82
X: 28 45 52 49 37 41 56 24
Fit a linear regression of Y on X and obtain the least square estimates of
the intercept and slope parameters. Also interpret the results (8+12)
 a.) The following data (Sample A and Sample B)denotes the age (in
months) at which infants walked alone from two populations A and B.
Sample A: 9.5 10.5 9.0 9.75 10.0 13.0 10.0 13.5 10.0 9.5 10.0 9.75
Sample B: 12.5 9.5 13.5 13.75 12.0 13.75 12.5 9.5 12.0 13.5 12.0 12.0
Do the above sample data support the hypothesis that the mean age at
which the infants walked alone is different in the two populations? Test
at 5% level.
b.) Consider a population with N=6 units, the values being 30, 22, 20, 15,
24 and 20. Select all possible samples of size 2 without replacement
and verify whether the sample range is an unbiased estimator for the
population range. (12+8)
 ) A sample of college students participated in a study designed to
evaluate the level of college students’ knowledge of a certain group of
common diseases. The following table shows the students classified by
their major field of study and level of knowledge of the group of
diseases.
Knowledge of Diseases
Major Good Average Poor
Premedical 85 58 30
Other 19 29 48
Do these data suggest that there is a relationship between knowledge of
the group of diseases and major field of study? Test at 5 % level.
b.) Draw a histogram and a frequency polygon for the following frequency
distribution.
Class Interval: 1019 2029 3039 4049 5059 6069
frequency: 4 66 47 36 12 4 (12+8)
 A remotivation team in a psychiatric hospital conducted an experiment to
compare five methods for remotivating patients. Patients were grouped
according to the level of initial motivation. The team assigned each patient
a composite score as a measure of his or her level of initial motivation. The
results were as follows:
Remotivation method
Level of initial motivation A B C D E
Nil 58 68 60 68 64
Very low 62 70 65 80 69
Low 67 78 68 81 70
Average 70 81 70 89 74
Do these data provide sufficient evidence to indicate a (i) difference in
mean scores among methods and (ii) mean scores among level of initial
motivation? Test at 5 % level.
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