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FARS Alcohol Results
The FARS data has a number of alcohol (and drug) fields — the fields ATST_TYP, ALC_RES relate actual test type, and results. To simplify things, I’ve added a derived field sALC_RES to breaks down test results into: negative, .01 through .07, and .08+, or no results. Most fatally injured drivers, cyclists, and pedestrians do get tested. (for those that are not, there are imputed results available from a separate data file, see below).
Note that the ALC_RES field, the numerical result, has changed over the years, before 2015, it was listed as the number of hundredths of a percent BAC, e.g. 0.12 was coded as 12. In 2015 and later, it is coded as thousandths of a percent BAC, so the same result would be listed at 120. The logic for this is encapsulated in the file 20xx_person.sql in the synthetic value sALC_RES: intox / not intox.
FARS and Drug Testing
The coding for drug results in FARS is similar to the alcohol scheme, except there are no quantitative results, only positive/negative. Also there is no equivalent to the imputation of results for drugs.
FARS coding: positive results for drugs shows up in the field DSTATUS=2 (i.e. “test given”) and DRUGRES1, 2, or 3 have a number up to 999; all in the person table. 0 meand test not given; 1 means No Drugs Reported/Negative. Potentially illicits are in groups generally in hundreds, e.g. 100-295 are narcotics, 300’s are depressants, 600’s cannaboids. Anything 996 or above are various meanings for unknown.
Examples: Zolpidem (Ambien) is 375. See pages 579-594 of the FARS Coding and Validation Manual.
FARS and Imputation of Alcohol Results
Driving while intoxicated has been recognized as a significant serious safety factor for decades; at the same time, it’s long been recognized that many involved in fatal traffic collisions (mostly drivers but sometimes peds and bicyclists) do not have recorded alcohol test results. This nhtsa report published in 2002 explains most of the deep background and terminology on the scheme to “fill in” missing results: Continue reading Use of alcohol as a risk factor for bicycling injury