Here's something you may not have in mind in voir dire: You can't count on math.

The statistics on "numeracy" -- our ability to work with numbers in everyday life -- are stark:

- Roughly a quarter of American adults can perform no more than "simple, one-step operations such as counting, sorting dates, performing simple arithmetic operations or understanding common and simple percents such as 50%."
- Another third are limited to "one-step or two-step processes and estimations involving whole numbers, benchmark percents and fractions, interpreting simple graphical or spatial representations, and performing simple measurements."

(All this is from an international 2003 study by the Organisation for Economic Co-Operation and Development. The 333-page report of the study is here.)

Let's use a little numeracy of our own here. Picture the jury box. Pretend it is full of people who perfectly represent the population. (It never is, but that's another essay.) Divide the box in half: front row, back row. Every single person sitting in in the front row, and likely one in the back row too, will have functional math skills falling somewhere between basic and nonexistent.

And it matters. If you watch mock trials, you see math errors tainting verdicts all the time. More than once I have watched an entire jury reach a damages number they clearly didn't intend, even using a calculator, because nobody knew how to figure out a royalty percentage, or a profit margin.

**It's not how many you say, it's how you say how many **

Of the many lessons here for lawyers, one was highlighted by a study released this week. It matters -- a lot -- how you choose to present numerical concepts to jurors.

In the study, University of Oregon students had to make decisions based on numbers. Each decision was presented two ways. When students were told, for example, that a psychiatric patient was to be released into the community, one group was told that similar patients had a 10% chance of committing violence, while a second group was told that for every 100 similar patients, 10 would commit violence. The second explanation made a much bigger impression, Prof. Ellen Peters explained:

"Low numerate people didn't see as much risk for Mr. Jones' potential for violence if told only that there is a 10 percent chance. We found that when low numerate people were told instead that there was a 10-in-100 chance, they could picture 10 people running around going crazy and realized that Mr. Jones may be one of them."

The researchers got the same results over and over, whether they presented the numbers in different words or different charts. Students made different decisions depending on how the same data was presented to them. They responded when words and pictures made the numbers real.