Is it improper for prosecutors (or for defense attorneys) to quantify the burden of proof in jury trials? Check out the recent case of People v. Van Meter (available here), in which a Colorado court of appeals reasoned as follows:
During voir dire, the prosecutor showed the potential jurors an incomplete puzzle of a space shuttle (with only sixty-six percent of the pieces present), stated that the image was a space shuttle “beyond a reasonable doubt,” and asked the potential jurors whether anyone disagreed, which none did; the prosecutor also showed the image during closing arguments. By using the iconic and easily recognizable space shuttle image, the prosecutor “invite[d] the jury to jump to a conclusion about [the] defendant’s guilt,” especially because the jury was shown an image and told that it was a space shuttle “beyond a reasonable doubt.” See alsoPeople v. Katzenberger, 101 Cal. Rptr. 3d 122, 127 (Cal. Ct. App. 2009) (concluding that a prosecutor improperly quantified the burden of proof by displaying an eight-piece puzzle of the Statue of Liberty missing two pieces and saying “this picture is beyond a reasonable doubt”). The prosecutor’s use of a two-thirds completed puzzle analogy also improperly quantified the burden of proof, even where the prosecutor did not undertake to quantify the number or percentage of missing pieces.
(Hat tip: Volokh Conspiracy.)
prior probability 
Interesting. I was on a jury a long time ago with a woman that did not understand “reasonable doubt”. Trying to get her to understand that no situation is 100% was difficult. I like the puzzle analogy, but I can see how it may sway a jury.
Totally true. What is “reasonable”—especially when reasonable persons can disagree!!??
I like the puzzle analogy but definitely think it was improper in front of a jury.
I need to think about this problem more, but the irony of this particular Colorado case is that the court of appeals did NOT overturn the conviction!
It is my understanding that the court concluded that it was prosecutor’s misconduct but because of other factors not prejudicial to the conviction so they did not overturn it. There is a warning for prosecutors to be cautious when going down this path. Reasonable doubt is a difficult concept. You need a simplified way to explain it to a jury.
True. Also, even without the use of the jigsaw puzzle, it’s very difficult (if not impossible) to formally define what “reasonable” is, since by definition, what is reasonable will vary depending on the life experience of each juror.