Confirmation Bias in DWI Field Sobriety Testing

The concept of confirmation bias occurs when a bias unconsciously influences the outcome of a test or observation. Instead of conducting a test objectively, someone is selectively looking for information or clues to confirm their pre-existing beliefs and hypotheses. 

Why is confirmation bias important in DWIs? Confirmation bias can play a large factor in a DWI arrest. Police officers are graded on their productivity. This is what drives most police officers to take more enforcement action. Knowing they have to be productive to meet their unspoken quotas, officers are often proactive in their enforcement activities.

Consider a police officer that gets behind a vehicle, runs the tag, and discovers the driver has had previous DWI convictions. Based on the driver’s record, the officer may assume the driver to be intoxicated. The police officer will look harder for a reason to justify a traffic stop. If the officer is able to initiate the traffic stop, that officer will immediately begin to look for signs of impairment, which may or may not be there.

In a situation such as this, typically, the officer will request the driver to submit to a roadside breath test. This is usually conducted before any standardized field sobriety tests (SFSTs) are conducted. The reason for this is because the officer knows it isn’t worth his time to conduct SFSTs if the driver doesn’t blow above a 0.08 during the roadside breath test. Often, an officer won’t initiate SFSTs unless the driver is above a 0.10 roadside. The officer knows that once they place the subject under arrest and transport them for their evidentiary breath test, their BAC may drop. The average person’s BAC drops between 0.015 to 0.018 per hour.

Although this technique, which is very commonly used, is not recommended by NHTSA, it is extremely effective. The officer will both save time and quickly determine whether the traffic stop will yield a DWI arrest. The problem is that a preliminary roadside breath test creates confirmation bias during the SFSTs. If the driver blows over a 0.08 during the preliminary breath test, the officer will look hard while conducting the SFSTs to find the clues he needs for arrest. Not only is this not good practice, the entire SFST battery will be jaded. The officer will not be conducting the tests objectively, but will be looking a reason to justify the arrest, whether one truly exists or not. 

Often, if confirmation bias can be established, the probable cause for the arrest may be negated. If the probable cause for the arrest is negated, the DWI charge may be dismissed. If you have more questions concerning confirmation bias in a DWI arrest, contact a DWI lawyer. 

Adkins Law is located in Huntersville NC and primarily serves Mecklenburg County and the Lake Norman area. If you need to speak with a DWI attorney in Huntersville NC, contact Adkins Law to schedule an appointment with a DWI lawyer. 

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