F 23 HEA 520 80 & 90 Module 9 Worksheet Answers (1)
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HEA 520 (80) & (90): Public Health Epidemiology
Fall 2023
Module 9: Experimental Studies Worksheet Answers
1.
The major purpose of random assignment in a clinical trial is to:
A.
Help ensure that the study subjects are representative of the general population
B.
Facilitate double blinding/masking
C.
Facilitate the measurement of outcome variables
D.
Ensure that the study groups have comparable baseline characteristics
E.
Reduce selection bias in the allocation of treatment.
2.
The purpose of a double blind or double masked study is to:
A.
Achieve comparability of treated and untreated subjects
B.
Reduce the effects of sampling variation
C.
Avoid observer and subject bias
D.
Avoid observer bias and sampling variation
E.
Avoid subject bias and sampling variation.
3.
Identify
two similarities
between a clinical trial and a prospective cohort study. Also,
note
two differences
between these two study designs.
Similarities
a)
Participants should be free of the outcome (DV/OV) at the initiation of the study.
b)
Participants are grouped into exposed and not exposed categories.
c)
All groups are followed for a period of time to determine outcome.
d)
Loss to follow-up can occur in both.
This is called lost-to-follow-up bias.
e)
Both provide incidence data (as ‘cause’ precedes ‘effect’ and temporality is
present) and so allow for calculation of risk. Hence, the measure of association is
Relative Risk for both study designs.
Differences
a)
Manipulation of exposure occurs in an experimental study but not in cohort
studies (which are observational).
b)
Randomization is essential to an experimental study design.
Absent in a cohort
study.
c)
Compliance with the intervention (prescribed by the study protocol) is essential in
an experimental study.
d)
Ethical challenges need to be addressed in experimental studies.
(Professor Zhang, UCLA, 2008)
4.
In a study to examine the benefits of treating mild hypertension (90-114 mmHg), a total
of 380 patients in a clinical trial were followed up for an average of 3.3 years.
Major
complications were observed in 56 of 194 controls, as compared to only 22 of 186 treated
subjects.
4.1
Develop a two-by-two table and fill up the cells and marginal totals with the data
provided.
Group
Complications
No Complications
Total
Treatment Group
22
164
186
Control Group
56
138
194
78
302
380
4.2.
Calculate the measure of association to show whether the treatment provided was
effective.
Complication rate in Treatment Group
=
22/ (22 + 164))
= 11.8%
Complication rate in Control Group
=
56/ (56 + 138)
= 28.9%
Relative Risk (RR)
=
(22/186)/ (56/194)
= 0.41
RR shows protective effect against complications.
How much?
4.3.
If the treatment was in fact effective, how effective was it?
Calculate the
appropriate measure of effect.
Difference in complication rate (Risk Difference)
=
11.8% - 28.9%= -17.1%
Treatment Group experienced 17.1% less complications than the Control Group.
5.
Indicate whether the following statements are
True
or
False
.
5.1.
A major advantage of a randomized experimental study is that it rules out self-
selection of subjects to the treatment and comparison groups.
True
5.2.
Randomization and random selection are alternative terms for the same concept.
False
_________________________________________________________
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