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Print date: February 12, 2016
EPI-820: Homework II - Evidence-Based Medicine
This homework consists of a combination of multiple choice and short answer questions. Each correct answer for
the multiple choice questions are worth 2 marks. Marks available for each short-answer question are indicated in
brackets e.g., (5). Some of the multiple choice questions ask you to identify more than one correct answer (indicated
by the statement “Which of the following statements are true”). Where space is given for the short-answer questions
please show your workings, as well as your final answer. Extra marks will be awarded for neat, easy to read
work! (N.B. Distant students may find it easier to fax their answers (517-432-1130).
1.
If a patient sees a clinician and complains of being sick:
a.
b.
c.
d.
2.
Which of the following statements are true:
a.
b.
c.
d.
e.
3.
The patients will always have a disease
The patients may or may not have an illness
The patient will always have an obvious sickness
Treating the underlying disease will always satisfy the patient.
Validity refers to the repeatability of a measurement.
Precision refers to the accuracy of a measurement.
Hard data should be repeatable.
A remedy for poor validity is to repeat the measurement.
A remedy for poor precision is to repeat the measurement.
You are trying to counsel Mrs. Jones, a thin, 55 year old, post-menopausal women to stop smoking. She has
been a pack-a-day smoker for 32 years, but feels fit and healthy and walks 3 miles every day. Her family
history and physical exam is unremarkable. She refuses to discuss taking menopausal estrogens, since her
sister had a “bad reaction” to them, and she defends her smoking habit by quoting a magazine article that
says smoking reduces the risk of endometrial cancer by one half. In order to make a convincing case for
her to quit, you do the following calculations:
You estimate the 10-year risk of lung cancer, coronary heart disease (CHD) and endometrial
cancer in a similar non-smoking women to be 0.1%, 8% and 1%, respectively. You find out the
relative risks (RR) for a pack-a-day smoker for lung cancer, CHD, and endometrial cancer to be
10, 2.5 and 0.5, respectively.
a. Complete the following table (4):
Lung CA
CHD
10-yr risk non-smoker
RR of smoking
10-yr risk smoker
Attributable risk (risk
difference) of smoking
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Endometrial CA.
b. Which of the three diseases is more causally related to smoking? Which measure indicates that? (2)
c. Which of the three diseases is more important in terms of clinical impact to Mrs. Jones? Which measure
tells you that? (2)
d. In words that Mrs. Jones can understand (she is after all, only a U of M graduate), explain what the data
in the table mean to her and why they make a convincing argument that she should quit smoking. (2)
4. The West of Scotland Coronary Prevention Trial (WOSCOP) study was a randomized clinical trial that tested
the efficacy of Pravastatin (a cholesterol lowering “statin” drug) in several thousand men with hypercholesterolemia,
but no previous history of coronary heart disease, over a 5 year period. There were 172 “events” in the 3,302 men in
the intervention arm, and 284 “events” in the 3,293 men in the placebo arm.
a. What was the Relative Risk Reduction of Pravastatin in this study? (2)
b. What is the Number-Needed-to-Treat (NNT) based on these results? (2)
c. What do you think would happen to the NNT if this trial were repeated in Scottish men who had neither
hypercholesterolemia nor a history of coronary heart disease? (1)
d. What do you think would happen to the NNT if this trial were repeated in Scottish men who had both
hypercholesterolemia and a history of coronary heart disease? (1)
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5. Two radiologists (Dr. Possibly and Dr. Maybe) independently reviewed 65 cervical radiographs for the presence
of vertebral canal stenosis. The two radiologists both agreed that stenosis was present in 7 cases and absent in 44.
Dr. Maybe identified 11 cases as having stenosis that Dr. Possibly called normal, while Dr. Possibly identified 3
cases as abnormal that Dr. Maybe called normal.
a. Construct the two-by-two agreement table (4).
b. What is the expected degree of agreement due to chance? (4)
c. Calculate the Kappa statistic and interpret (4).
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6.
Tachycardia is always present in hyperthyroidism. Which of the following are true?
a.
b.
c.
d.
e.
7.
A disease may be excluded from consideration because:
a.
b.
c.
d.
e.
8.
it is rare.
a 100% specific test is negative.
a 100% sensitive test is negative.
a test for a competing disease is positive.
a test for a competing disease is negative.
The presence of a disease may be absolutely confirmed if:
a.
b.
c.
d.
e.
9.
The clue is 100% specific.
The clue is 100% sensitive.
The presence of the clue diagnoses the disease.
The absence of the clue excludes the disease.
None of the above.
it is very common.
a 100% specific test is positive.
a 100% sensitive test is positive.
the case resembles the classic disease pattern.
all of the above.
A test for the presence of cancer has an 80% true positive rate and a 2% false positive rate.
a. Of 25 patients with cancer, how many can be expected to have a negative result? (2)
b. Of 50 patients known not to have cancer, how many will have a negative result? (2)
c. When used to screen 5000 people, only 1% of which have cancer, how many positive tests will be
found? Of these how many will actually have cancer? What is this measure called? (4)
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