TO: Students in CJ 160

FROM: R. B. Taylor

DATE: 1/31/00

RE: BAC levels

One of the points that Jacobs makes is that with the per se laws for drunk driving, you cannot necessarily know when you are breaking the law. In class on 1/27/00 I attempted to demonstrate this point. I asked each of you to estimate for me how many 12 ounce beers you would need to drink in two hours in order to push your BAC limit beyond the .10% threshhold that defines DUI in this state. I asked you then to provide me with the following information, in addition to the number of beers: your weight, rounded to the nearest ten pounds, and your gender. You then submitted that information anonymously on 3X5 cards. Pat McConnell then entered the data and sent them along to me. 69 responses were received (29 females, 40 males) with 68 reporting the estimated number of beers and 68 reporting their weight. Number of beers ranged from 1 to 10, with an average of 4.15 and a median (middlemost score) of 4.0. Weight reported ranged from 95 to 245 with an average of 162 and a median of 160.

Were there gender differences? Yes there were. As you might expect, the males estimated a significantly higher number of needed beers (mean=4.6 beers) compared to the women (mean=3.5 beers) (t(df=65.67)=2.85; p < .01, two tailed). But since the males weighed significantly more, this difference is not that surprising (mean male weight = 178.6; mean female weight reported=139.1; t(df=59.4)=5.89; p < .001). Do men estimate a higher number of beers after we control for the weight difference? No. After controlling for the weight difference between the males and females the number of beers estimated was about the same (t=-1.07; p > .25).

How many exceeded the BAC of .10%? The way I set up this exercise, you got a "correct" answer if you guessed just the right number of beers to push you just over the limit. I was able to calculate your BAC using your gender, your weight, and the number of beers reported.⁽¹⁾ As you can see from the formula, your BAC will be higher: * the more alcohol you drink; * the lower your weight; * if you are female; and the shorter the time period in question. (Here the time period was the same for everyone.) The distribution on BAC ranged from around 0 to .17% (mean=.076). Of the 68 usable responses, 17 or 25% provided an answer that generated a BAC level of .10 or higher. So 75% provided answers that were too low. Since the BAC also went up to .17, some of the 17 answers abover .10 were way above, and thus too high.

Gender differences on exceeding BAC of .10%. Interestingly enough, the women respondents in the class were more likely to generate a BAC of .10 or over with their beer estimates. Whereas only 4 of the 40 males (10% of the males) provided answers generating a BAC of .10 or higher, 13 of the 28 women or 46.4% of the women provided answers generating a BAC of .10 or higher. This difference is statistically significant.⁽²⁾ You can see these differences in the two figures displayed below.

The point? Does this help you better understand Jacobs' point? Can you follow why the men drink more but are less likely to be DUI; i.e., a smaller percentage of the group will be over .10%

PS - As a result of this exercise please do not drink more before you drive! Remember, your BAC level may not connect closely with your ability to operate a motor vehicle.

1. The formula that is used is

BAC(h) = [(A/(r*p))/10] - (h*k)

where

BAC(h)=Blood alcohol concentration at time h (in hours)

A =grams of ethanol consumed which is equal to

[(liquid ounces of alcohol) * (.82)]/.035]

r =reduced body mass (.68 for males; .55 for females)

p =weight in kilograms (pounds/2.2046)

h =hours drinking

K =estimate rate at which body metabolizes ethanol (.015 ounces per hour)

 

1 ounce of ethanol is equal to

* 24 ounces of beer

* 7 ounces of wine

* 2 ounces of 100 proof (50%) liquor

 

Source: Greenfield, L. A. (1988) Drunk Driving. Bureau of Justice Statistics Special Report. Washington: Bureau of Justice Statistics

2. Which, if you have $3.59, might get you coffee in a paper cup at Starbucks.