Copyright © 2009 The Cochrane Collaboration. Published by John Wiley & Sons, Ltd.
A. The width of the horizontal lines in each study indicates the risk ratio for each study
B. The confidence interval of the test for overall effect crosses 1. This finding suggests there is significant mortality benefit of treating hypertensive patients with beta-blockers compared to placebo
C. To be included in the meta-analysis, studies need to be relatively heterogeneous for meaningful comparison
D. The size of a square in each study indicates the confidence interval of each study in meta-analysis
E. The overall estimated effect of all of the studies in a meta-analysis is represented by a diamond at the bottom of the graph
11. In a city with a population of 10 000, the results of a new diagnostic test for tuberculosis are given below. Which one of the following is the positive predictive value (PPV) of the diagnostic test in this group of patients?
| Tuberculosis | ||
|---|---|---|
| Test result | Present | Absent |
| Positive | 1800 | 4000 |
| Negative | 200 | 4000 |
A. 50
B. 31
C. 90
D. 18
E. 45
12. A new laboratory test for a disease has a sensitivity of 90% and a specificity of 80%. Which one of the following is true concerning this new test?
A. 90% of patients who do not have the disease will have a negative result
B. If the test is positive, the probability of the disease being present is 90%
C. 10% of patients who have the disease will have a positive result
D. If the prevalence of the disease in the population is 1%, in screening this population over 90% will be false positives
E. Increased laboratory error increases the predictive value of the test
Theme: Statistical test (for Questions 13–15)
A. Log-rank correlation
B. Spearman’s rank correlation
C. Wilcoxon signed-rank test
D. Mann-Whitney U-test
E. Chi-squared test
F. Logistic regression analysis
G. Paired Student’s t-test
H. Unpaired Student’s t-test
For each of the studies described below, select the most appropriate statistical test.
13. A study is testing the effects of a new drug A on hypertension. Two groups of hypertensive patients are recruited. One group is treated with drug A for 3 months while the other is not. The study evaluated the reduction of blood pressure after treatment between the two groups. What is the most appropriate statistical test to use for this study?
14. A research fellow is assessing the effectiveness of a new therapy for squamous cell carcinoma (SCC) and recruits newly diagnosed SCC patients to the study. She randomises the total participants to either the existing treatment or the novel treatment arm and performs the standard operation for melanoma excision on the first group (n = 420). She also performs the newly proposed therapy on the second group (n = 390). The treatment arms are double-blinded (both to the researcher and patients); 6 months after the surgery the patients are seen in clinic to assess for recurrence rates. The data shown below are obtained. Which one of the statistical tests would be most suitable for investigating the effect of the novel treatment?
| Disease present | Yes | No |
| Standard treatment | 80 | 340 |
| Novel treatment | 60 | 330 |
15. The frequency of attendance of 50 basic physician trainees at a weekly educational session was recorded by an observer over a 1-year period. The trainees were assessed at the end of this period with a multiple choice examination with a test score marked out of 100. Which statistical test is the best to evaluate the effectiveness of trainees’ attendance on higher examination scores?
Answers
Basic Science
1. Answer B
The attributable risk of hyperlipidaemia in patients who had myocardial infarction (MI) in the study group is 23%. The attributable risk is the difference in incidence of MI between those with and without hyperlipidaemia, i.e. 25% – 5% = 20%.
The relative risk is the ratio of those who had a MI in the hyperlipidaemia group to those who had a MI with hyperlipidaemia (0.25/0.05 = 5). A relative risk of greater than 1 implies that hyperlipidaemia is associated with an increased risk of MI, but does not necessarily imply causation.
The attributable risk of hyperlipidaemia in patients who had myocardial infarction (MI) in the study group is 23%. The attributable risk is the difference in incidence of MI between those with and without hyperlipidaemia, i.e. 25% – 5% = 20%.
The relative risk is the ratio of those who had a MI in the hyperlipidaemia group to those who had a MI with hyperlipidaemia (0.25/0.05 = 5). A relative risk of greater than 1 implies that hyperlipidaemia is associated with an increased risk of MI, but does not necessarily imply causation.
2. Answer A
Range, standard deviation and variance are common measures of dispersion. The standard deviation is the most widely used measure of the spread of data about their mean. The larger the standard deviation, the more spread out the distribution of the data about the mean.
The range is the measurement of the width of the entire distribution and is found simply by calculating the difference between the highest and lowest values. The range gives no information about the distribution of the values.
In a skewed distribution, the extreme values will affect the mean to a larger degree than they will affect the median. In a normal distribution, 68% of the values should fall between one standard deviation in either direction and over 95% of the values should fall between two standard deviations in either direction.
The variance is the square of the standard deviation and a measurement of the variation among all the subjects in the sample.
Range, standard deviation and variance are common measures of dispersion. The standard deviation is the most widely used measure of the spread of data about their mean. The larger the standard deviation, the more spread out the distribution of the data about the mean.
The range is the measurement of the width of the entire distribution and is found simply by calculating the difference between the highest and lowest values. The range gives no information about the distribution of the values.
In a skewed distribution, the extreme values will affect the mean to a larger degree than they will affect the median. In a normal distribution, 68% of the values should fall between one standard deviation in either direction and over 95% of the values should fall between two standard deviations in either direction.
The variance is the square of the standard deviation and a measurement of the variation among all the subjects in the sample.
3. Answer C
Incidence is the number of newly affected individuals in an at-risk population over a given time (often assumed to be 1 year). Prevalence is the number of cases of a particular disease or condition at a specified time in an at-risk population. Lifetime prevalence is the proportion of a population that at some point in their life (up to the time of assessment) have experienced the condition.
Incidence is the number of newly affected individuals in an at-risk population over a given time (often assumed to be 1 year). Prevalence is the number of cases of a particular disease or condition at a specified time in an at-risk population. Lifetime prevalence is the proportion of a population that at some point in their life (up to the time of assessment) have experienced the condition.
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