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From: g woodall
Password: orange
Date: 24 Aug 2009
Time: 15:25:01 -0700
Remote Name: 199.227.125.3
He still gets tested. However at some point you might wonder about just how random is the process being used. A quarterly selection for a single annual 1/2 testing rate makes selection probability 1/8 for selection one time in one quarter, and 5/8 for selection one time in 5 quarters (1/8+1/8+1/8+1/8+1/8). As each quarter goes by, there are fewer remaining quarters in which to be selected, so the probability of selection changes accordingly. For example, after one quarter goes by, the probability of selection one additional time is 4/8. And, after two quarters, the probability of selection one additional time is 3/8. This gentleman has been selected 3 times within 5 quarters which could occur by chance 1/9 times (5/8 x 4/8 x 3/8 = 1/9). You might have calculated a probability of 1/512, but that would be for getting selected 3 out of three times, not 3 of 5 times. Small populations and sample size can also skew. By my math, this one is not yet significant.