Estimating alcohol impairment in the field: implications for drunken driving.

As they left a fraternity party, 93 college-age students were asked to estimate their blood alcohol level (BAL) and to report whether they were legally impaired. They were also asked to report the number of 10-oz cups of beer they had consumed during the party. Actual BALs were tested on a Breathalyzer and the subjects' self-reported number of cups were compared with the cup-by-cup consumption data collected during the party. The results indicated that many subjects were able to report correctly whether they were legally impaired. However, those subjects with higher BALs tended to overestimate their actual BAL while underestimating the number of cups of beer they had consumed. These results are discussed in terms of the ability of individuals to make judgments about their level of impairment. The implications of these results for the prevention of drunken driving are also addressed.