LETTER
Pooling of trials is not appropriate in the case of heterogeneity
University Medical Centre, Lundlaan 6, Utrecht, the Netherlands; c.w.bollen@umcutrecht.nl
Keywords: high frequency ventilation; bronchopulmonary dysplasia; preterm; meta-analysis
| The first 150 words of the full text of this article appear below. |
We read with great interest the systematic review by Thome et al1 on the elective use of high frequency ventilation compared with conventional mechanical ventilation in preterm infants. Thome et al included 17 randomised trials and stated that, unlike previous meta-analyses, they did not find significant benefits in pulmonary outcome. They also referred to our published cumulative meta-analysis.2 However, we would like to point to the fact that, in our meta-analysis, we reported the same finding, but we restricted pooling to subgroups according to ventilation strategies used for both high frequency ventilation and conventional mechanical ventilation. The reason we did not pool all studies was because there was considerable heterogeneity between studies. The use of random effect models to overcome the problem of heterogeneity is debatable.3 Thome et al showed an odds ratio of 0.87 with a 95% confidence interval of 0.75 to 1.00. Strictly speaking, the effect of high
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