Hetherington J, Dickersin K, Chalmers I, Meinert CL (1989)

Retrospective and prospective identification of unpublished controlled trials: lessons from a survey of obstetricians and pediatricians. Pediatrics 84(2):374-80.
Report of an attempt to obtain information about unpublished trials in perinatal medicine by writing to 42,000 obstetricians and pediatricians in 18 countries, which concluded that publication bias would not be addressed successfully by attempts to obtain information about unpublished trials retrospectively.

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