next up previous
Next: The rationale behind the Up: On the Paper of Previous: The significance levels in

Random partitions

I considered a random partition of the 66 Rabbis from the two tests together into one part of 34 Rabbis and another part of 32 Rabbis, and studied the distribution of the ratios of the P2 scores for the two groups and, in particular, how likely it is that such a ratio is smaller than 1.1217, the ratio of the numbers reported by WRR.

The distribution of the ratio of P2 statistics is quite interesting. The probability that this ratio is below 1.1217 is roughly 1/100. (More precisely it is 0.0092, but see the technical remark in Section 7.) Note that this is a direct Monte Carlo estimate and it does not rely on any probabilistic assumptions. The median value of the P2-ratio is roughly 700. The average is huge due to rare occurrences of very high ratios and I cannot estimate it. The average of the logarithm (with base 10) is roughly 3.3 .

As an illustration, if you move Rabbi number 7 (Rabbi David Ganz) from the first to the second list (and it is agreed that he was on the first list by mistake (see [1]) according the criteria of WRR,) the ratio in question changes to 4.1268. As another illustration, the ratio we observe will be obtained by multiplying one out of the 152 distances of the first experiment by 0.66, and leaving all other 151 distances as they are.

Remark: We compute the probability that the ratio between the two P2-scores will be smaller than 1.1217. Of course, if we restrict our attention only to cases where the P2-score of the second test is smaller than that of the first test this further resuces the probability roughly by a factor of two.


next up previous
Next: The rationale behind the Up: On the Paper of Previous: The significance levels in
Gil Kalai
9/2/1997