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A guide on meta-analysis of time-to-event outcomes using aggregate data in vascular and endovascular surgery
George A Antoniou1, Stavros A Antoniou2, Catrin Tudur Smith3
1Department of Vascular and Endovascular Surgery, The Royal Oldham Hospital, Pennine Acute Hospitals NHS Trust, Manchester, United Kingdom; Division of Cardiovascular Sciences, School of Medical Sciences, University of Manchester, Manchester, United Kingdom.
Background:
Time-to-event outcomes measure not only whether but also when an event happens. They are commonly used to evaluate vascular therapies, where the events of interest include disease recurrence (eg, loss of graft patency), reintervention (eg, target lesion revascularization), or death. Meta-analyses of published time-to-event outcomes are most appropriately measured by hazard ratios (HR).
Methods:
We constructed a guide to increase awareness and adoption of these methods in vascular and endovascular surgery research, make systematic reviewers familiar with the basic principles of time-to-event data meta-analysis, and provide information about useful resources.
Results:
Commonly, values of HR are not provided in published studies, but there are methods available to obtain such values and associated statistics from published summary data. Both direct and indirect methods can be applied to calculate the HR and its variance or standard error. Once individual study estimates of HR and its variance (or standard error) have been obtained, a pooled estimate of the log HR and variance can be calculated using the inverse-variance method.
Conclusions:
Time-to-event data should not be analyzed as dichotomous data. Such meta-analyses need to account for time and the differential censoring of the subjects. The HR is the preferred treatment effect measure. A mixture of direct or indirect methods can be applied to calculate the individual study estimates.