Contamination

In a trial in which an individual or group is allocated to receive or not to receive an intervention, 'contamination' is essentially defined as the influence of an intervention on a subject not intended to receive the intervention. For example, suppose patients within a GP practice are randomized to receive or not to receive dietary advice aimed at reducing their risk of bowel cancer. If individual patients allocated no intervention become aware that others are being treated differently, then...

Relative and absolute measures of effect

The hazard ratio introduced in Section 9.3.4 is a relative measure of effect. Thus, when comparing two treatments, an experimental and control, a hazard ratio of 0.75 represents a 25 per cent reduction in the relative risk of an event on the experimental group compared to the control group at any given time. This is a useful scale on which to conduct and report analyses. In reporting results it is useful to report an absolute difference as well as this relative difference. It is not good...

Test for interaction

As mentioned above the appropriate test to perform when considering subgroups is a (single) test for interaction assessing the consistency of the overall effect across the groups, rather than a separate test for significance for each subgroup. Although the basic principles are the same, the exact details of the test vary with the type of data. The basic principles are that the estimate in each subgroup is compared with the overall estimate from the whole trial. The squared difference of this...

Assessing maturity and reliability of data

The Kaplan-Meier survival curves for the BA06 bladder cancer trial 3 are shown in Fig. 9.4. The report gives the median follow-up of patients still alive at four years. We can see from this figure that the curves, and therefore their comparison, are still reliable at five years (an important timepoint in this disease), since the total numbers at risk in the chemotherapy and no chemotherapy groups at five years are ninety-three and eighty, respectively. In the design, the plan was to reliably...

Example of an IPD metaanalysis Postoperative radiotherapy in nonsmallcell lung cancer

Beta Blockers And

Introduction Worldwide, over half a million new cases of lung cancer are diagnosed each year 58 and it is the leading cause of cancer deaths. Surgery is the treatment of choice for non-small-cell lung cancer (NSCLC), and around one fifth of tumours are suitable for potentially curative resection 59 . However, even for patients with apparently completely resected disease, survival rates are disappointing - around 40 per cent at two years. In an effort to improve both local control and survival,...