RBH1
Module: Hypothesis testing
Instructions: Please write down your answers in this document. Take care that you save the
copy of the document on your local PC BEFORE you start writing. At the end of the practical
send the document to ibz@mefst.hr.
Exercises
1. A randomised controlled trial evaluated the cost and efficacy of community leg ulcer
clinics that used four layer compression bandaging. The control treatment was
provision of usual care by district nurses. Over the 12 months of follow-up, ulcers
healed more quickly in the clinic group than in the control group (P=0.03). Statistical
tests were two sided.
Which of the following, if any, are true?
a) Null hypothesis: in the population, over 12 months of follow-up healing times are
shorter if leg ulcers are treated in community clinics rather than by district nurses
b) Null hypothesis: in the population, no difference exists between community clinics
and district nurses in the healing times of leg ulcers over 12 months of follow-up
c) Alternative hypothesis: in the population, over 12 months of follow-up leg ulcers
take longer to heal if treated by district nurses rather than in community clinics
d) The P value represents the strength of evidence in support of the null hypothesis
2. Define the null hypothesis and the alternative hypothesis for an example of your
choice (1 one-sided and 1 two-sided example).
3. Put the stages of doing a hypothesis test into the correct order
A. Interpret the P-value
B. Calculate the test statistic
C. Define the null and alternative hypotheses
D. Collect the relevant data
True or false?
4. Comparing hypothesis tests and confidence intervals
A. Hypothesis tests are easier to calculate
B. A confidence interval does not tell you about the significance of the results
C. A hypothesis test gives an idea of the precision of the results whereas the
confidence interval cannot
D. A hypothesis test gives you an idea of the likely magnitude of a population
parameter whereas a confidence interval cannot
5. What is the difference between a one-tailed test and a two-tailed test?
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6. Match the study questions (1–5) to the most appropriate statistical test. Use table from
Appendix 1 (at the end of this document)
Options
A. ANOVA
B. Chi-squared test
C. Two-sample z-test
D. Paired samples t-test
a. A new drug for lowering mean blood pressure is being compared with a placebo in a
crossover trial
b. Is there a higher risk of breast cancer in women who take the pill versus women who
do not?
c. Is the proportion of smokers different in France, Britain and Germany?
d. Is the mean BMI of 15-year-olds in Scotland greater than the mean BMI of 15-yearolds in England?
e. Three different drugs for the treatment of hypercholesterolemia are being compared
using mean cholesterol levels across the groups
7. What does a P-value of > 0.05 mean?
8. Write in your own words a sentence to explain what is meant by: “The two treatments were
found to be statistically significantly different”?
9. What does it mean to say:
“A 95% confidence interval for an antibiotic treatment’s infection eradication rate is from
82% to 90%”?
10. If a 95% confidence interval for a difference in eradication rates between two treatments
is from -1.5% to + 13.5%, what is the conclusion of a hypothesis test of whether there is no
difference between the treatments?
11. Explain the findings – Will you recommend bronchodilator to your patients?
Two hundred adults seeing an asthma nurse specialist were randomly assigned to either a new
type of bronchodilator or placebo. After 3 months the peak flow rates in the treatment group
had increased by a mean of 96 l/min (SD 58), and in the placebo group by 70 l/min
(SD 52). The null hypothesis is that there is no difference between the bronchodilator and the
placebo. The t statistic is 11.14, resulting in a P value of 0.001.
12. Fill in missing words
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A GP introduced a nurse triage system into her practice. She was interested in finding out
whether the age of the patients attending for triage appointments was different to that of
patients who made emergency appointments with the GP.
Six hundred and forty-six patients saw the triage nurse and 532 patients saw the GP. The
median age of the triaged patients was 50 years (1stquartile 40 years, 3rd quartile 54), for the
GP it was 46 (22, 58).
The graph in Fig. 9 shows the ages of the patients.
The statistician used a ________________________ to test the hypothesis that there is
____________________________ between the ages of the two groups. This gave a U value
of 133 200 with a P value of < 0.001.
Results suggest that the triage nurse’s patients were very highly significantly _________ than
those who saw the GP.
13. Based on the clinical trial result, which antibiotic will you recommend to your
patients suffering from bronchopneumonia?
A group of patients with bronchopneumonia were treated with either amoxicillin or
erythromycin. The results are shown in Table 3.
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Appendix 1. Which test to use?
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