What this means is that if the play has already had n performances at the point in its run when you happen to see it, you can be 95 percent sure that it has no more than 39 × n performances to go and no fewer than n ÷ 39. (This is a matter of elementary arithmetic: the upper limit keeps you out of the first 2.5 percent of the total audience, and the lower limit keeps you out of the last 2.5 percent.) With nothing more than the Copernican principle and a grade school calculation, you can come up with a 95 percent confidence interval for the longevity of something like a Broadway play. That is
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