What could be expected from systematic reviews on individual patient data?
Introduction: Some examples have shown how the availability of individual patient data in systematic reviews could modify the treatment effect estimate. The enhancement of data reliability is an obvious advantage of this approach. We present here some examples of other advantages, linked with the possibility of multivariate or survival modelling. Methods/Results: We collected data from 11 randomised controlled trials that assessed antihypertensive drug interventions on cardiovascular morbi-mortality. The corresponding data base concerns 53,799 hypertensive people included between 1972 and 1990, cumulates more than 270,000 person years of follow-up, during which 5,487 major clinical events have been observed. Example l: We explored if treatment effect, expressed as hazard ratio, was constant over time. Significant variations were observed, which were in opposite directions than what was expected a priori: the treatment effect significantly increased with time in stroke, whereas it decre
