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Bronchopulmonary dysplasia and care techniques.

To the Editor.—
 Although the paper by Avery et al1 is both interesting and provocative, readers should be cautioned about the inherent limitations of data generated by a retrospective, multicentered study design.
 First, the definition of chronic lung disease leaves much to be desired. The diagnosis was "arbitrarily defined" as an oxygen requirement greater than room air at 28 days of age. Evaluation of the need for oxygen at 3 months is a much more clinically relevant end point, but the numbers in this category were too small to evaluate adequately.