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Follow-up Exercises for Session Three: EBM 811:
1. Drug A is being compared to Drug B in the treatment of malignant hypertension. The
hypothesis that there is no difference in blood pressure reduction between the two
agents is termed:
a. the assumption
b. the null hypothesis
c. Type I error
d. the alternate hypothesis
e. the relative risk ratio
2. Drug A is being compared to Drug B in the treatment of malignant hypertension. The
hypothesis that there is greater than 5 mm mercury difference in blood pressure
reduction between the two agents is termed:
a. the assumption
b. the null hypothesis
c. Type I error
d. the alternate hypothesis
e. the relative risk ratio
3. Drug A is found to reduce blood pressure greater than Drug B by 5 mm with p =
0.05. The p means:
a. the chance is < 5% of the therapy being effective
b. Drug A is 5% (i.e. 5 mm) more effective than Drug B
c. the chance of seeing this result is <5% if there is no real difference
d. the power of the study
4. Based on this study, we conclude that Drug A is significantly better than Drug B in
reducing blood pressure. If, in fact, we are wrong and there really is no difference
between the drugs we have committed:
a. a type I error
b. a type II error
c. a null hypothesis
d. an alternate hypothesis
e. a mortal sin
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5. The risk of a Type I error is:
a. the p value
b. alpha
c. the chance of a false positive study
d. all of the above
6. Would you use Drug A or Drug B? Why _______________________________
_______________________________________________________________
7. The smaller the treatment effect:
a. the smaller the study needs to be
b. the larger the study needs to be
c. has no effect on study size
8. In another study, Drug A is found not to reduce blood pressure greater than Drug B.
(p > 0.05) If, in fact, there is a real difference, we have committed:
a. a type I error
b. a type II error
c. a null hypothesis
d. an alternate hypothesis
e. a misdemeanor
9. The risk of a Type II error is:
a. the p value
b. alpha
c. the chance of a false negative study
d. all of the above
10. Fifty male and 50 female patients were asked if they preferred a male or female
nurse to assist with their care using a Likert scale as below.
1
2
3
4
5
Prefer
Male
Exclusively
Prefer
Male
Some
Doesn’t
Matter
Prefer
Female
Some
Prefer
Female
Exclusively
Results revealed:
Male
Mean = 2.93
Female
Mean = 3.12
P= .75
The author concluded that patients did not care if the nurse was male or female. Do you
agree?
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
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11. Drug A is found to reduce the five year mortality from MI by 45% . Drug B however
in comparison is found to only reduce the actual mortality by 1%. Drug C is under
investigation and is promising to save one patient life for every 100 patients treated.
Which drug do you choose? Why?
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
12. The mean GCS of patients requiring neurosurgical operative intervention was found
to be 11. In those patients not requiring intervention, the mean was 13. A Student’s ttest was used and this difference was found to be significant. (p<0.05)
Do you believe this?
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
13. Match the statistical test and its description:
a. Students t test
b. Wilcoxon rank sum test (Mann-Whitney U test)
c. Chi-square test
d. Fisher’s exact test
e. One-way ANOVA
f. Kruskal-Wallis
_____ Used to test whether or not the means of measurements from two groups are
equal. assuming that the data are normally distributed and that the data from both
groups have equal variance.
_____ Used to test whether two sets of observations have the same distribution. These
tests are similar in use to the t test, but do not assume the data are normally distributed.
_____ Used with categoncal variables (two or more discrete treatments with two or
more discrete outcomes) to test the null hypothesis that is no effect of treatment on
outcome. assumes at least 5 expected observations of each combination of treatment
and outcome, under the null hypothesis.
_____ Used in an analogous manner to the chi-square test, this test may be used even
when less than 5 observations are expected in one or more categories of treatment and
Outcome.
_____ Used to test the null hypothesis that three or more sets of continuous data have
equal means. assuming the data are normalily distributed and that the data from all
groups have identical variances.
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_____ This is a non-parametric test analogous to the one-wax ANOVA.
No assumption is made regarding normality of the data. The
test may be thought of as a Wilcoxon rank sum test for three or more groups.
14. Drug A is found to reduce blood pressure greater than Drug B by 20.0 mm with
95% confidence interval 5.4-28.2. This means:
a. Drug A is equivalent to Drug B
b. the p value is between 5.4 and 28.2
c. the true range of blood pressure reduction might be 5.4 to 28.2 mm Hg
d. a type I error has occurred
15. A 95% confidence interval that includes zero treatment difference implies that
a. there is a statistical but not clinical difference
b. there is a clinical but not statistical differnece
c. there probably is no statistical differece in the two groups
d. there is a clear advantage to one treatment over the other
16. One study finds a 20% absolute improvement in mortality for a treatment compared
to placebo with 95% confidence intervals -5% to 35%. The Study had a p > 0.05. What
do you conclude? _________________________________________
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
17. Another study finds a 20% absolute improvement in mortality for a treatment
compared to placebo with 95% confidence intervals 15% to 28%. . What do you
conclude? ______________________________________________________
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
18. A third study finds a 0% absolute improvement in mortality for a treatment compared
to placebo with 95% confidence intervals -5% to 5%. The Study had a p > 0.05. What
do you conclude? ________________________________________
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
19. Drug A is found to reduce blood pressure greater than Drug B by 2 mm Hg with
95% C.I. of 1.8 to 2.1 mm.
a. there is a statistical but not clinical difference
b. there is a clinical but not statistical differnece
c. there probably is no statistical differece in the two groups
d. there is a clear advantage to one treatment over the other
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20. In a study to determine antibiotic effectiveness, 200 patients are given either A or B
antibiotic randomly assigned. Of those 100 patients taking A, 100 completed the course
and 50 improved resulting in a 50% treatment effectiveness. Of those 100 patients
taking B, 50 completed the course and 25 improved resulting in a 50% treatment
effectiveness in those that took the drug. The authors conclude that the drugs are
equally effective. Do you agree? Why? _________________________
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
21. Discuss the difference between a therapy “A” that reduces mortality from 2% to 1%.
(a 50% relative risk reduction) and a therapy “B” that reduces mortality from 50% to
25% ( a 50% relative risk reduction). __________________________________
________________________________________________________________
________________________________________________________________
________________________________________________________________
22. The Absolute risk reduction for therapy A is 2% - 1% = 1%. You would have to treat
how many patients to benefit one patient?
a. 1
b. 4
c. 100
d. 1000
23. The Absolute Risk Reduction for therapy B is 50% - 25% = 25%. You would have to
treat how many patients to benefit one patient?
a. 1
b. 4
c. 100
d. 1000
24. If you are selling Drug A, how do you “spin” the results of the above study?
________________________________________________________________
________________________________________________________________
________________________________________________________________
25. We found a correlation between blood pressure and mortality with R = 0.5. The
increased mortality accounted for by this blood pressure elevation was:
a. 5%
b. 25%
c. 50%
d. 75%
e. not enough information
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26. The degree of correlation found (0.5) is:
a. strong
b. moderate
c. weak
d. negligible
27. Due to the correlation found in problem # 25, we can say that elevated blood
pressure is the cause of increased mortality.
a. true
b. false
28. Data from a new drug indicate:
Placebo
Drug
Death Rate
20%
10%
The baseline death rate without the drug is ________%
The RRR for death is _______________ %
The ARR for death is _______________
The NNT for death is _______________
29. Data from the same drug indicate:
Placebo
Drug
Hair Loss Rate
10%
50%
The baseline hair loss rate without the drug is ________%
The “RRR“ for hair loss is _______________ % ** note the sign!!**
The “ARR” for hair loss is _______________
The “NNT” for hair loss is _______________
When the sign is NEGATIVE this implies that the therapy has risk and we rename the
RRR to RRI (relative risk increase) and ARR to ARI (absolute risk increase)
The NNT becomes NNH (number needed to harm. For the above, we need to treat 10
to save one from death with the risk of causing hair loss in every 2.5 persons treated
Session Three
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