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Data were collected from a national sample of 66 out of 100 NEISS hospitals that were selected as a stratified probability sample of United States hospitals with at least 6 beds that provided 24-hour emergency service excluding psychiatric and penal institutions. The sample included five strata of which four represented different levels of hospital size, measured by the number of emergency department visits. The fifth contained the children's hospitals. There were 31 hospitals in the small stratum, 9 hospitals in the medium stratum, 6 hospitals in the large stratum, 15 hospitals in the very large stratum, and 5 hospitals in the children's stratum.