LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – STATISTICS

SECOND SEMESTER – APRIL 2012

ST 2960 – BIO-STATISTICS

 

 

Date : 24-04-2012             Dept. No.                                        Max. : 100 Marks

Time : 9:00 – 12:00

 

SECTION – A

Answer ALL the questions                                                                                 (10 x 2 = 20 marks)

1. Mention the broad types of observational studies.
2. Explain the term ‘Concurrent Control’ in Clinical Trials.
3. State the need for adjusting rates.
4. Explain the term ‘Prevalence’ of a disease.
5. State the use of Kappa statistic and give its form.
6. Name the two tests used to test equality of means when the same group is measured twice.
7. Express ‘baseline category logit’ in terms of ‘adjacent-categories logits’.
8. Write the link equation for the ‘proportional odds cumulative logit model.
9. State the difference between Actuarial Analysis and  Kaplan- Meier Method  in survival data

Analysis.

10. Give the estimate for ‘Hazard Rate’ when survival distribution is exponential.

 

SECTION – B

Answer any FIVE questions                                                                                 (5 x 8 = 40 marks)

11. Describe the different ‘Scales of Measurement’ with examples.
12. The following two-way table is obtained from an experiment conducted to study the effect of

a drug ‘A’ in reducing the risk of a disease:

Outcome Risk factor	Disease	No Disease	Total
Drug ‘A’	71	5448	5519
Placebo	119	5395	5514
	190	10843	11033

 

 

 

 

 

 

Compute  Experimental Event Rate,  Control Event Rate,  Relative Risk  and   Absolute Risk

Reduction and interpret the results.

13. Investigators wished to know if  there was  a significantly  higher Insulin  sensitivity among

people with normal weight compared to overweight people. The following measurements on

insulin sensitivity were obtained from 11 normal-weight people and 8 overweight people:

Normal-Weight subjects: 0.97, 0.88, 0.66, 0.52, 0.38, 0.71, 0.46, 0.29, 0.68, 0.96, 0.97

Overweight subjects: 0.76, 0.44, 0.48, 0.39, 1.10, 0.19, 0.19, 0.19

Carry out Wilcoxon Rank Sum Test and draw your conclusions.

(Cont’d)

14. A medical initiative was started in a certain locality two years ago. Among 300 people in the

locality, 178 supported  the initiative at  the start of  the program but at present the number of

people supporting it is 142. And among the original supporters only 96 continue their support

now while the remaining are opposing it. Form the contingency table to apply McNemar Test

and draw the appropriate conclusion.

15. Discuss the two approaches to compare proportions in two groups.
16. Apply the Levene Test to compare the variances of the two populations (of normal-weight

subjects and overweight subjects) based on the sample observations given in Q. No. (13).

17. Discuss the baseline category logit model for nominal multinomial response variable. Obtain

estimates for probabilities of membership of an individual to the various response categories.

18. For the data in Q.No. (22) apply the Actuarial Method to estimate the survival function for

patients under Therapy ‘B’, considering time-windows of 180 days.

 

SECTION – C

Answer any TWO questions                                                                              (2 x 20 = 40 marks)

19. Describe ‘Cohort Studies’, ‘Historical Cohort Studies’ and ‘Clinical Trials with Cross Over’.

Present schematic diagram for each of these designs.

 

20. (a) The following table gives the data on infant deaths observed in three regions over a time-

period:

.                                         Region A                              Region B                             Region C                      .

.       Birthweight           Births          Deaths            Births           Deaths           Births          Deaths

.                                  (in 1000.s)                           (in 1000’s)                           (in 1000s)                          .

< 1500 g                   30                1280                 60               3605                 40               5020

1500-2499 g              45                  710                 90                1780                70               1960

≥ 2500 g                   225                1540               130                1155             110               1220        .

Total                         300                3530               280                6540              220               8200       .

Find the ‘Crude Infant Mortality  Rate’ for each region.  Compute ‘Adjusted Infant Mortality

Rates’  by  direct  method for Regions B and C  treating  Region A  as  reference population.

Supposing that the  Age-Group-Wise  ‘Specific Infant  Mortality  Rates’  for B and C  are  not

available, find  ‘Standardized Infant Mortality Ratios’  for  these two  regions again  keeping

A as the reference population.

(b) Explain the Large Sample Sign Test.                                                                         (12 + 8)

 

21. The condition of patients brought to the head-injury unit of a hospital are classified into

four categories:

1 – mild injury (not requiring hospitalization)

2 – moderate injury (requiring hospitalisation)

3 – severe injury (requiring intensive care)

4 – very severe injury (resulting in ‘coma’ state / death)                                           (Cont’d)

A continuation-ratio logit model was built based on past data collected from the hospital

and the following logit equations were obtained:

Log = –0.004 + 0.058*age – 0.003*BP + 0.128*D_H – 0.573*D_R – 1.14* D_2w – 0.532*D_Blood

Log  = 0.009 + 0.074*age – 0.014*BP + 0.421*D_H – 0.718*D_R – 0.92* D_2W – 0.612* D_Blood

Log  = 0.022 +  0.082*age – 0.037*BP + 0.613*D_H – 0.838*D_R –  0.23*D_2W – 0.751*D_Blood

where D_H  indicates  injury at  home, D_R   indicates  injury while walking  on the  road, D_2W

indicates injury while riding two-wheeler and  D_Blood indicates the patient was bleeding. BP

is the systolic blood pressure measured at the time of being brought to hospital.

Estimate the probabilities for a 45 year old man, bleeding, with BP = 140 who was  injured

while on two- wheeler to be classified into each of the four injured categories.

 

22. Patients with prostate carcinoma (tumour) are subject to two types of therapy (A and B). The

interest among investigators  is  on  the  ‘survival time’ of  the patients.  Data on 20 patients

observed for a maximum period of 5 years are given below:

Patient	Days in study	Therapy	Outcome
Name Name Name Name Name   Name Name Name Name Name   Name Name Name Name Name   Name Name Name Name Name	97 159 213 255 303   425 494 620 715 760   895 930 1007 1102 1163   1304 1413 1490 1595 1676	A B A A B   B B A B A   B A B B A   A A A A A	Dead Dead Dead Alive Alive   Alive Alive Dead Alive Alive   Alive Alive Dead Alive Dead   Alive Dead Alive Alive Dead

Apply the Logrank test to compare the survival distributions of patients under the two therapies.

 

 

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