Everything has happened at least once, but I never saw anything remotely approaching this sort of error in twenty years of U.S. litigation. An expert who made this error would get torn apart in a deposition, and I can't imagine a court allowing an expert to present that source of statistical error to a jury unless it was never brought to the court's attention.

One would hope not and that any errors would be at least slightly more subtle. I dunno but there is this on wiki

https://en.wikipedia.org/wiki/Prosecutor%27s_fallacy

My dad gave expert testimony on one ocassion when the judge summed up what he said totally wrongly and then threatened my dad with contempt of court for shaking his head (probably noisely).

If you are presenting statistics in a methodologically defensible way, then you have leeway. You are not allowed to present blatant math errors to a jury in the United States.

In other words, if an expert for the other side made the error you describe, in 99.9% of cases, you either would be able to get the expert struck entirely or the Court would preclude the expert from offering opinions that repeated the math error.

You also would have an exceedingly difficult time finding an expert who was willing to make that sort of error intentionally. If you are a professional expert, it is very bad for business if your opinion is excluded by a court. If that happens a few times, your career as an expert is diminished significantly. When you are looking for an expert, one of your first questions is "has a court ever excluded your opinion?" If the answer is yes, it's a big red flag, especially if you are looking for an opinion on a closely related topic.

Not really a Passport discussion at this point....or any point within the past several days.

I am closing this thread.

Further Covid related posts should go into the thread HERE