Letters

Neonatal risk factors for cerebral palsy in very preterm babies

BMJ 1997; 314 doi: https://doi.org/10.1136/bmj.314.7094.1624 (Published 31 May 1997) Cite this as: BMJ 1997;314:1624

Time oriented analyses of risk are useful

  1. Elizabeth N Allred, Instructor in neurology, Harvard Medical Schoola,
  2. Olaf Dammann, Research fellow in neurology, Harvard Medical Schoola,
  3. Karl Kuban, Assistant professor of neurology, Tufts Medical Schoola,
  4. Alan Leviton, Professor of neurology, Harvard Medical Schoola,
  5. Marcello Pagano, Professor of statistical computing, Harvard Medical Schoola
  1. a Neuroepidemiology Unit, Children's Hospital, 300 Longwood, Boston, MA 02115, USA
  2. b Department of Obstetrics and Gynaecology, St Michael's Hospital, Bristol BS2 8EG

    Editor—Deirdre J Murphy and colleagues recently reported a case-control study comparing 59 children with cerebral palsy with 234 without.1 One of their key messages was “Neonatal pneumothorax, sepsis, and transfusion are associated with preterm cerebral palsy independently of adverse antenatal factors.” We are not convinced that they have shown an independent effect.

    To identify the contributions of exposures and characteristics occurring at one time independent of the contributions of exposures and characteristics that occur later, we have performed time oriented logistic regression analyses in which risk factors are ordered in a temporal pattern. The earliest occurring predictors and covariates of the outcome are entered first and are not displaced by covariates occurring later.2 An odds ratio significantly different from 1 for the variable occurring later suggests that it contributes risk …

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