Sample selection bias in the emergency room: an examination of the role of alcohol in injury

Abstract

Aims: Injury location, injury cause and patient drinking patterns were used to predict blood alcohol content (BAC) and self-reported drinking before injury using emergency room (ER) data.

Design: Models estimating both BAC and self-reported drinking among emergency room injury patients were used; the ER sample was also compared to an injured sample from the general population.

Setting: Data were from three of six communities participating in the project "Preventing Alcohol Trauma: a community trial".

Participants: ER data were collected from nine hospitals on Friday and Saturday nights between 6 p.m. and 2 a.m. on alternate weekends from June 1992 to December 1995. Telephone survey data were collected between April 1992 and March 1996.

Measurements: Drinking measures included drinking frequency, drinks per occasion, and variance. Other measures involved injury time, location, and type; drinking before and after injury; and age, race, gender, education, marital status and household income. Model estimation corrected both for selection bias and censoring of the dependent measure.

Findings: The results indicate: (1) ER populations tended to be female, less well educated, non-white, poor and younger; (2) there were significant selection bias effects in the ER sample; (3) assaults were more likely to involve drinking than other injury types; (4) drinking patterns were significant non-linear predictors of alcohol involvement; and (5) self-reported drinking before injury was both a sensitive and specific indicator of measured BAC.

Conclusions: Assaults uniquely involve the use of alcohol and selection bias may threaten ER study validity.