Transcript Module III.6.2-Interpretation of the epidemiological data

IAEA Post Graduate Educational Course Radiation Protection and Safe Use of Radiation Sources
Biological Effects of Ionizing Radiation
Epidemiological Studies and
Issues
Interpretation of the epidemiological data
Practical exercise
IAEA Post Graduate Educational Course Radiation Protection and Safe Use of Radiation Sources
Content


Tasks to be solved
Correct answers
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Task 1

a)
b)
c)
d)
e)
Classify the study described in the note
to the slide as to the following:
Cross-sectional study
Case control study
Concurrent cohort study
Retrospective cohort study
Randomized clinical trial
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Task 2

The absolute difference between the
food-specific attack rate of those who ate
a certain food and those who did non eat
it is essentially:
a)
b)
c)
d)
e)
An incidence rate
A prevalence rate
A relative risk
An attributable risk
None of the above
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Task 3

A case control study of the association
between smoking and myocardial
infarction (MI) gave the following results:
Diseas
None status smokers
MI
No MI
Smokers
Number of packs smoked per
day
1/2
1
2
31
9
39
18
2,706
710
1.825
605
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Task 3 – Cont’d



Calculate the estimated relative risk of
MI, with non-smokers as the reference
group, for those smoking 5 packs / day
Calculate the the estimated relative risk
of MI, with non-smokers as the reference
group, for those smoking 1 pack / day
Calculate the estimated relative risk of
MI, with non-smokers as the reference
group, for those smoking 2 packs day
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Task 4

In a study of all cases of a disease, of the
relative risk for the association between a factor
and the disease is equal to or less than 1.0 then:
a)
There is no association between the factor and the disease
The factor protects against development of the disease
Either matching or randomization has been unsuccessful
The comparison group used was unsuitable and a valid
comparison is not possible
There is either no association or a negative association
between the factor and the disease
b)
c)
d)
e)
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Task 5

The main purpose of randomization in the
study described in the note to the slide is to:
a)
b)
c)
d)
e)
Minimize placebo reactions
Avoid bias in the assignment of treatment
group
Make the efficacy of the vaccine equal in the 2
groups
Minimize vaccine reactions
Insure that the rates on influenza observed in
the 2 groups will be the same
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Task 6

The most practical and efficient way to eliminate
differences between the cases and controls with
regard to sex in the study described in the
note to the slide would be:
a)
b)
c)
d)
e)
Repeat the selection of cases and controls, matching
for sex
Calculate incidence rates for stomach cancer
separately for males and females
Exclude males from the study
Classify study subjects according to sex, and compare
prior radiation exposure among cases and controls for
each sex
Re-do the study using a stratified random assignment
to exposure or non-exposure to assure equal numbers
of males and females in each group
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Task 7

Which of the following is an advantage of a case
control study:
a)
b)
c)
d)
e)
There is a little or no bias in assessment of exposure to
the factor
It is possible to study more than one exposure at a time
Multiple disease outcomes following a selected
exposure can be readily studied
This study design is useful for studying rare exposures
Recall bias is easily avoided
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Task 8

A study is planned of the relationship of
maternal diabetes to the risk of a certain
congenital malformation in the offspring. All of
the following would argue for using a cohort
design except:
a)
b)
c)
d)
e)
A potential recall bias
Validity of information regarding the immediate postconceptual period
The low rate of this congenital malformation
Precise monitoring of diabetic control early in
pregnancy
The need to obtain data on early fetal losses
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Task 9

“Any systematic error in the design,
conduct or analysis of a study that
results in a mistaken estimate of an
exposure’s effect on the risk of disease”,
is a definition of:
a)
b)
c)
d)
e)
Confounding
Bias
Interaction
Stratification
None of the above
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Task 10

A history of active exercise was compared for
women with hip fracture and unmatched
controls. Active exercise in the previous 2 years
was reported by 31% of the cases and 46% of the
controls. What is the association between hip
fracture and active exercise?
a)
b)
c)
d)
e)
Relative risk – 0.67
Relative risk – 1.48
Odds ration – 0.53
Odds ratio – 1.90
None of the above
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Task 11

Attributable risk is:
a)
b)
c)
d)
e)
The risk of a population group possessing a
characteristic, as a multiple of the group lacking the
characteristic
The number of cases that are explained by a given
factor
The ratio of the incidence rates in those exposed to a
factor compared to those not exposed to the factor
The proportion of disease risk accounted for a given
factor
The ration incidence rates in those not exposed to a
factor compared to those exposed to a factor
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Task 12

Gallum and Paffenbarger reported that a total of
98 cases of coronary heart disease (CHD)
occurred in 13,728 Harvard students enrolled in
a study during 1939-1950, and followed until
December 31, 1973. Based on these data, it can
be inferred that:
a)
b)
c)
d)
e)
The crude mortality rate for CHD was 98/13,728 per year
The case fatality rate for CDH was 98/13,728
The period prevalence rate for CHD was 98/13,728
The incidence rate for CHD was 98/13,728 per year
None of the above
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Task 13


In 1980, there were 5,000 deaths due to
emphysema in male cotton workers aged
20-64 in South Carolina. The expected
number if deaths in this occupational
groups, based on age-specific death rates
from emphysema in all males aged 20-64
in the US during 1980, was 2,500.
What was the standardized mortality ratio
(SMR) for emphysema in the male cotton
workers?
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Task 14


In 1985, the community of Tombstone passed a
special law requiring the use of car safety seats for
infants and mandatory seatbelt use for children
under the age of 19. In the table below are the
number of deaths due to motor vehicle accidents and
the total population in 1980 (before the law) and in
1990 (5 years after the law was enacted).
What is the age-specific mortality rate due to motor
vehicle accidents for children aged 0 to 18 years in
1980:
a)
b)
c)
d)
e)
1.8 per 1000
2.9 per 1000
4.0 per 1000
6.1 per 1000
Can not be calculated from the given information
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Task 14 (Cont’d)
Age, years
1980
1980
1990
1990
N of motor Population N of motor Population
vehicle
vehicle
deaths
deaths
Under 3
25
2,000
10
2,000
3-18
60
12,000
20
8,000
19-49
60
33,000
120
30,000
50+
55
55,000
250
80,000
Total
200
102,000
400
120,000
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Task 15

Calculate the age-adjusted death rate per 100,000 in
the 2 populations by the direct method using totals of
both populations as the standard population
Age
Population A
Population B
N of
people
N of
deaths
N of
people
N of
deaths
30-49
500,000
60
300,000
30
50-69
300,000
396
400,000
400
70+
100,000
406
200,000
700
Total
900,000
862
900,000
1,130
Crude death
rate
96 / 100,000
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126 / 100,000
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Task 16

Drug A is currently used to treat disease X and
has a 15% cure rate. A drug company claimed
that a new drug B has a 30% cure rate. With the
help of the table below, you are reviewing the
results of a randomized clinical trial in which
such a difference was detected. In this trial, 50
patients were enrolled in each therapy group and
drug A had a 15% cure rate and drug B had a 30%
cure rate. The p-value for the difference was 0.15
and the study’s investigator concluded that there
was no statistical difference between drug A and
B. Which of the following statements should you
make in your review:
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Task 16 (Cont’d)

Which of the following statements should you
make in your review:
a)
b)
c)
d)
The conclusion was incorrect because p-value for the
observed difference was greater than 0.05
The study didn’t have sufficient power to conclude that
the difference was not statistically significant
The study had sufficient power to find this statistical
difference
The conclusion was incorrect because it was possible
that sicker people chose to be part of the group
receiving drug B
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Task 17

In a study of a Peruvian migrants to the
US, the following SMRs* were found to
disease Y:
Native Peruvians living in Peru – 625%
 Peruvian migrants to US – 95%
 US born children of Peruvian ancestry – 100%
 US born children of non-Peruvian ancestry –
100%
* - expected values for calculation of SMRs are
derived from the general US population

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Task 17 (Cont’d)

These findings suggest that:
a)
b)
c)
d)
e)
Genetic factors are the major determinants of
these SMRs
Environmental factors are the major
determinants of these SMRs
Migrants are highly representative of the
population I their native country
A protective factor against disease Y is
present in the Peruvian environment
None of the above
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Correct answers for the Tasks
Task N
Correct answer
Task N
Correct answer
1
b
10
c
2
d
11
d
12
e
3
1.11; 1.865; 2.60
4
e
13
2 or 200%
5
b
14
d
6
d
15
7
b
8
c
16
b
9
b
17
b
124.3 per 100,000
101.7 per 100,000
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Summary

This exercise presented tasks to be
solved after learning the lecture in the
field of Epidemiology issues

Comments are welcomed
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Where to Get More Information



dos Santos Silva I. Cancer epidemiology:
principles and methods. WHO, IARC,
France 1999
Methods in observational epidemiology.
Eds. Kelsey J.L., Whittemore A.S., Evans
A.S., Thompson W.D., New York, Oxford
University Press, 1996
The Johns Hopkins University School of
Hygiene and Public Health. Graduate
Summer Institute of Epidemiology and
Biostatistics, Training Materials
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