Solution to MCQ Self Test 3

```1. TTTTF   2. TFTTT   3. TTTFF   4. TTFTT
```

Score +1 for a correct answer, -1 for an incorrect answer, and 0 if you did not answer. This will give a total mark out of 20. You can rate your performance as follows:- below 7: work much harder, 8-9: work harder, 10-13: adequate, 14-16: very good, 17-18: excellent, 19 or more: take over the class.

Notes on the questions

1. (a) The pooled estimate is the meta-analysis odds ratio summarising the three studies. (b) The difference between 0.1 and 1 is the same as the difference between 1 and 10, i.e. a factor of 10 is represented by a constant difference on the scale (c) This is the convention for this style of figure. (d) The difference is significant if the confidence interval does not include 1.0, the null hypothesis value of the odds ratio (e) On the contrary, we should try to get all studies which have been carried out, whether published or not, to avoid publication bias.

2. (a) We can have three treatments in random order, or four, or even more, though it gets difficult to organise and to keep the subjects interested. (b) The order is randomized. (c) because the variation between patients is removed, we have a much more accurate treatment comparison and so need fewer patients. (d) the treatment should not change the disease, because then we could not apply the second treatment, so this design is best for chronic diseases rather than acute. (e) We compare the results on both treatments for the same patient.

3. (a) We need this so that we know which studies to analyse. (b) This is the usual starting point (c) We need to get all the studies, whether published or not, otherwise we may have a biased sample of the available. Studies are more likely to be published if they show significant differences (publication bias) (d) Unpublished studies are less likely to include significant treatment differences than published ones, so these differences are likely to be smaller. (e) Papers published in English are more likely to include significant differences, another aspect of publication bias.

4. (a, b) Each circle and horizontal line represent the observed difference and its confidence interval. (c) Studies with long horizontal lines have wide confidence intervals and so should be given least weight (d) The confidence interval for the combined estimate does not include zero (e) All the confidence intervals for the individual trials include zero.

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