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The Pediatric Forum
October 2004

Outcomes After “Benign” Extra-Axial Fluid—Reply

Arch Pediatr Adolesc Med. 2004;158(10):1017. doi:10.1001/archpedi.158.10.1017-b

In reply

We thank Dr Harkavy for his careful reading of our article. First, we appreciate the difficulty in the use of the word control to describe the reference group in any epidemiologic study. Dr Harkavy refers to a control group as in a randomized trial where there is an intervention; however, as seen in the use of the word control in case-control studies, a control group can also refer to any population of patients to whom the study is comparing the group of interest.1 In our study, we chose to focus on the population of infants with macrocephaly who were examined at a pediatrician’s office or in a neonatal follow-up group. Our “cases” were those infants with the conditions of interest (ie, benign extra-axial fluid). Thus, our “controls” were those infants without extra-axial fluid. We realize that to answer other questions a different cohort of patients should be recruited. For example, to ascertain the true incidence and effect of extra-axial fluid in children receiving ECMO, the appropriate control group would be infants treated with ECMO who did not develop extra-axial fluid. Because of the significant number of infants lost to follow-up in most neonatal follow-up programs, we were concerned about the potential biases in doing this study.