Stephen Gustitis recently commented on a study done at Berkeley that ‘debunk[ed] conventional wisdom on trial witnesses’:

The researchers concluded that self-assured witnesses who make a mistake – even on issues of little importance – undermine their credibility by raising doubts about their competency, their ability to judge their own abilities and their motivations.

"People giving testimony, or advice, or opinions should therefore be careful to express appropriate degrees of confidence in their assertions," the researchers write in a summary of their report in the January issue of the journal Psychological Science. "Otherwise, the 13th stroke of the clock will cast the other 12 in doubt."

I take issue with the title of that article, because I doubt that is the conventional wisdom, at least of those who should know. As Stephen says, the study ‘confrimed what experienced criminal defense lawyers already knew’:

The cocky, arrogant, or over-confident witness builds a wall between themselves and the jury. Since normal, ordinary, and reasonable people know we all make mistakes, the over-confident witness projects an air of superiority which juries tend to resent. Consequently, when the witness is caught in a mistake the jury is quite happy to punish him by greatly devaluing his credibility.

The over-confident witness is often one testifying as an expert, but the problem also affects the lay witness. The experienced defense lawyer preparing these witnesses for court will recognize the problem and take appropriate steps to temper their over-confidence.

100% correct. And this leads me to one of my favorite things about DWI cases. Since DWI is an opinion crime, the arresting officer will find himself caught up in this phenomenon in almost every case.

When it comes to evaluating a defendant’s performance on the field sobriety tests, yes, NHTSA has their ‘standards’, but even the manual doesn’t attempt to suggest that everyone will do perfectly. Or even that all defendants who exhibit X number of clues on the [HGN, Walk and Turn, One Leg Stand, etc.] are intoxicated.

Consequently, when asked in cross examination whether my particular client could have exhibited the clues on videotape, but not be intoxicated, the officer has two choices:

(1)   He can admit it’s possible that things other than intoxication could have caused my client’s ‘errors’ on the test.

(2)   He can express with 100% confidence and certitude that the only reason for my client’s foot coming off the imaginary line is absolute proof of intoxication.

Frankly, I’m fine with either answer. In a lot of cases, I prefer answer #2. Jurors know #2 is wrong wrong wrong; and as the study suggests, it will reduce the juror’s natural tendency to ‘believe what the officer says’.

In fact, seasoned officers know this as well. In my experience, almost all of the Austin DWI Task Force officers will testify either at pretrial or at the ALR hearing that the tests are not 100% accurate, and that factors other than alcohol or intoxication can cause some missteps on the FSTs.

Of course, that’s not really such a bad answer either.

[Also see: Certainty of the Witness.]