Arbitrary numbers

Some interesting uses of arbitrary numbers have come up in the news recently. The threshold used for the PSA test for prostate cancer was chosen "just sort of arbitrarily" (via Educated Guesswork). The threshold was set very low in an effort to catch cancers early while they're still most treatable, but now it's becoming clear that the correlation between such low levels of PSA and cancer is much weaker than previously believed.

Also in the news this week is that the launch codes for America's nuclear missiles was set to 00000000, and this fact was (relatively) widely known. I know this wasn't the only layer of security, and maybe it's not true (perhaps a select few knew the real code, but spread rumors of this fake one), but I'm still amazed sometimes that we haven't managed to blow ourselves to smithereens yet.