Tuesday, April 22, 2008

Retrograde Extrapolation in California DUI cases - under .08?

California DUI attorneys regularly deal with the concept of retrograde extrapolation.

Your California DUI blood-alcohol concentration level (BAC) is below the .08 percent legal limit at the time you provide a California DUI breath or blood test at the jail or police station.

Will you still be prosecuted for California DUI? Will you need a California DUI lawyer?

Or your BAC is lower at the time of that required California DUI implied consent test than it was at the time of a roadside breath (preliminary alcohol screening aka PAS) test.

You wonder how your true BAC can be proven at time of driving based on a California DUI test done later.

It’s a definite California DUI issue. One can try to guess what the true BAC was in a California DUI case by projecting backwards, using average alcohol absorption and elimination rates, but it’s only an inaccurate guess based on assumptions.

It's called "retrograde extrapolation" — a pretty name for trying to guess backwards. The San Diego DUI prosecutor in a California DUI trial often offers BAC test evidence guessing one's BAC...back to the time of driving.

The blood-alcohol level at the time of a California DUI chemical test is not relevant to the California DUI charge. The California DUI prosecutor therefore attempts offer evidence to show what the BAC was when the California DUI arrestee was actually driving.

This is commonly done by “extrapolating” backward - i.e. computing the earlier blood-alcohol level by estimating how much alcohol had been eliminated or “burned off” in the period between California driving and California DUI testing.

But retrograde extrapolation requires two California DUI assumptions:

(1) The California DUI arrestee's blood-alcohol level was declining; and
(2) The California DUI arrestee's the rate of elimination is known.

This second California DUI assumption further involves the California DUI prosecution lab employee's (aka expert's) assumption that the “burn-off” rate was .015 percent per hour (sometimes the assumed rate is .02 percent).

Over the California DUI Defense Attorney's objection, how does the California DUI prosecution know that the California DUI arrestee was eliminating (assuming he or she was eliminating rather than still absorbing) at that rate and not at .005 percent, .3 percent or some other possible scientific rate?!

Quite simply, the California DUI prosecuting lawyer does not know. The California DUI attorney prosecutor's laboratory employee merely assumes that the California DUI arrestee was eliminating and that he or she eliminated at the average rate.

The California DUI problem is that everyone has a different metabolism, and even a given person will metabolize alcohol at different rates depending on many variables.

In one important study, researchers found a wide range of metabolism rates: some individuals can absorb alcohol and reach peak blood-alcohol levels ten times faster than others. (Kurt Dubowski, “Absorption, Distribution and Elimination of Alcohol: Highway Safety Aspects”, Journal on Studies of Alcohol (July 1985)).

As a result, legitimate California DUI scientists conclude that the practice of estimating earlier BAC levels in California DUI cases is highly inaccurate and should be discouraged in most California DUI attorneys' cases.

California DUI breath test defenses are found at http://www.sandiegodrunkdrivingattorney.net/defenses.html .