SAMPLE SELECTION BIAS IN THE EMERGENCY ROOM - AN EXAMINATION OF THE ROLE OF ALCOHOL IN INJURY

Aims. injury location, injury cause and patient drinking patterns were used to predict blood alcohol content (BAG) and self-reported drinkin g before injury using emergency room (ER) data. Design. Models estimat ing both BAC and self-reported drinking among emergency room injury pa tients were used; the ER sample was also compared to an injured sample from the general population. Setting. Data were from three of six com munities participating in the project ''Preventing Alcohol Trauma: a c ommunity trial''. Participants. ER data were collected from nine hospi tals on Friday and Saturday nights between 6 p. m. and 2 a. m. on alte rnate weekends from June 1992 to December 1995. Telephone survey data were collected between April 1992 and March 1996. Measurements. Drinki ng measures included drinking frequency, drinks per occasion, and vari ance. Other measures involved injury time, location, and type; drinkin g before and after injury; and age, race, gender, education, marital s tatus and household income. Model estimation corrected both for select ion 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 bia s effects in the ER sample; (3) assaults were more likely to involve d rinking than other injury types; (4) drinking patterns were significan t non-linear predictors of alcohol involvement; and (5) self-reported drinking before injury was both a sensitive and specific indicator of measured BAG. Conclusions. Assaults uniquely involve the use of alcoho l and selection bias may threaten ER study validity.