184s Abstracts

Three recently developed techniques of chart construction were compared with a chart constructed from a multilevel model to see which method produces centiles which fit the data best. the HRY method using spline procedure is shown to produce the best tit, and this technique has been used to construct the growth charts of weight and height for Iranian boys and girls. However, growth of rural children differs significantly from that of children in urban Iran; a practical solution enabling one set of charts to be used for both groups of children is proposed. In view of the differences between the Tehran charts and the NCHS references, it is concluded that charts presented here should be adopted as the new reference curves for children in Iran.

P120 INDIVIDUAL PATIENT DATA META-ANALYSES FOR

TIME-TO-EVENT OUTCOMES: AN EXAMPLE FROM EPILEPSY

Paula Williamson, Jane Hutton, Anthony Marson, and David Chadwick University of Liverpool

Liverpool, United Kingdom

The confidence intervals from randomized trials of valproate versus carbamazepine for patients with partial or generalized epilepsy are wide, and as a consequence important differences in efficacy have not been excluded, nor can equivalence be inferred. For a planned meta-analysis considerations included: (1) that such a variety of seizure outcomes had been reported that it was not possible to perform a meta-analysis using data from reports; (2) that the main efficacy measures [(i) time to first seizure, (ii) time to 6, 12, 24 month remission from seizures, (iii) time to withdrawal of allocated drug] are time-to-event outcomes and it was uncertain whether aggregate data would be sufficient; (3) that with two main types of seizure, multiple endpoints are a potential problem.

There is a widely held belief that carbamazepine is more effective for patients with partial epilepsy whilst valproate is better for generalized epilepsy and this is the primary hypothesis for the meta-analysis. Collecting individual patient data would provide greater power to test for a treatmentcovariate interaction. Individual patient data were thus sought and results will be presented using data collected from five of the trials involving 837 partial and 393 generalized epilepsy patients, representing over 90% of all those known to have been randomized to either valproate or carbamazepine. Particular attention will be paid to consistency of results with different endpoints.

There are important methodological issues within meta-analysis of individual patient data. For example, since seizure data are usually collected in terms of the number and type of seizures between visits, data entry errors may be more of a problem here than in trials where mortality is the main endpoint. A comparison will be made between results from the meta- analysis of unchecked data straight from the author and of check data (with inconsistencies resolved). This work should make a useful contribution to the debate surrounding the need for individual patient data with time-to-event outcomes.

P121 AGGREGATE PATIENT DATA META-ANALYSES WITH

TIMETO-EVENT ENDPOINTS: AN EXAMPLE FROM SURGERY

Paula Win, Deborah Ashby, Carrol Preston, Saboor Khan and Robert Sutton University of Liverpool

Liverpool, United Kingdom

For trials with time-toevent outcomes, meta-analysis with individual patient data may be viewed as the gold standard. However, time and financial constraints may preclude this. An example might be where the me&analysis was to inform the interim review of an ongoing trial.