Field Sobriety Test Statistics and Admissibility

THE OKOROCHA FIRM * December 30, 2025 Forensic Toxicology

Article overview: Field Sobriety Test statistics and other statistics/averages/ranges for the hypothetical generality of the populace, as distinguished from matters provable as to the individual defendant, infect the record with a fatal error. In People v. Wilson (2019) 33 Cal.App.5th 559 it was held that it was…

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Field Sobriety Test statistics and other statistics/averages/ranges for the hypothetical generality of the populace, as distinguished from matters provable as to the individual defendant, infect the record with a fatal error.
In People v. Wilson (2019) 33 Cal.App.5th 559 it was held that it was error to admit statistical-likelihood evidence to convict the defendant:
“Thus, it appears that the clear weight of authority in our sister states, the federal courts, and the military courts finds such evidence inadmissible. We find the reasoning of these cases compelling. Dr. Urquiza’s testimony had the effect of telling the jury there was at least a 94 percent chance that any given child who claimed to have been sexually abused was telling the truth. And, although Dr. Urquiza’s testimony on this point was not expressly directed to either L.D. or J.D., the practical result was to suggest to the jury that there was an overwhelming likelihood their testimony was truthful. In so doing, this testimony invaded the province of the jury, whose responsibility it is to ‘draw the ultimate inferences from the evidence.’” People v. Wilson (2019) — Cal.App.5th —, — [2019 Cal. App. LEXIS 265, *22, 2019 WL 1373728]

The holding in Wilson is supported by a previous ruling in which it was held mathematical probabilities cannot support convictions because they invade the province of the jury and are not particularized to the defendant on trial.
“We deal here with the novel question of whether evidence of mathematical probability has been properly introduced and used by the prosecution in a criminal case. While we discern no inherent incompatibility between the disciplines of law and mathematics and intend no general disapproval or disparagement of the latter as an auxiliary in the fact-finding processes of the former, we cannot uphold the technique employed in the instant case. As we explain in detail, infra, the testimony as to mathematical probability infected the case with a fatal error and distorted the jury’s traditional role of determining guilt or innocence according to long-settled rules. Mathematics, a veritable sorcerer in our computerized society, while assisting the trier of fact in the search for truth, must not cast a spell over him. We conclude that on the record before us defendant should not have had his guilt determined by the odds and that he is entitled to a new trial. We reverse the judgment.” People v. Collins (1968) 68 Cal.2d 319, 320 [emphasis added].

See also People v Julian (2019) 34 CA5th 878, 885 (statistical probability evidence that Child Abuse Accommodation Syndrome (CAAS) leads to false accusations only small percentage of time was highly prejudicial “predictive conclusion” and failure to object was ineffective assistance of counsel).

Why field-sobriety percentages cannot convict

Published sensitivity, specificity or validation percentages describe study populations and controlled conditions; they do not establish guilt in an individual case. The actual administration, scoring, medical factors, environment and officer interpretation still must be proved and challenged.

Continue with the field-sobriety-test evidence guide.