Field Sobriety Test Defense in DUI Cases

Prosecutors frequently rely on studies claiming that SFSTs have been “validated” as reliable indicators of impairment.

One commonly cited study involved Colorado law enforcement participation and purported to validate officer arrest decisions following SFST administration.

However, these studies contain important limitations that are rarely explained to juries.

For example:

• officers generally did not administer SFSTs to every driver stopped,
• the studies often involved additional independent evidence of impairment,
• and researchers typically evaluated only cases where officers decided to arrest.

Importantly, the studies often did not evaluate:

• whether officers were wrong when they chose not to arrest someone.

That creates a major selection bias problem.

Putting it another way:

• officers are already making arrest decisions based on driving behavior, admissions, odor of alcohol, and other observations,
• and the studies often focus only on whether arrests later corresponded with elevated BAC results.

Critics argue this does not necessarily prove the SFSTs themselves caused the accurate decision.

Theoretically, if officers:

• already suspected DUI,
• and randomly arrested some drivers based on a coin flip,
  the study might still appear to “validate” arrest decisions because the initial suspicion was based on other evidence entirely.

The studies therefore do not always isolate whether the SFSTs themselves are independently reliable.