The bias I saw would likely be difficult to exploit without studying the mathematics a lot more. It seems to pass several statistical tests, but the problem I found was more about independence.
Let's call the two splits L for left and R for right and consider the resulting deck to be defined as a sequence of these letters indicating whether that card was taken from the left or right pile so in theory you can specify a shuffle uniquely like "LRRLLLLLLRRR...". This method of labeling shuffles has the advantage of being extremely easy to record and also makes the bias I found apparent where there are way too many pairs of "LR" and "RL" compared to "LL" and "RR" like the "7 shuffles is enough" model suggests there should be.
For some reason, when I did all this analysis last year, I was mostly thinking about how to ensure my MTG decks are sufficiently shuffled. I didn't really think about the implications for card counting. However, normal riffle shuffling seems to have less bias (but still present) than the mash shuffling I looked at and I think most casinos use machines for shuffling these days.
Comments
The bias I saw would likely be difficult to exploit without studying the mathematics a lot more. It seems to pass several statistical tests, but the problem I found was more about independence.
Let's call the two splits L for left and R for right and consider the resulting deck to be defined as a sequence of these letters indicating whether that card was taken from the left or right pile so in theory you can specify a shuffle uniquely like "LRRLLLLLLRRR...". This method of labeling shuffles has the advantage of being extremely easy to record and also makes the bias I found apparent where there are way too many pairs of "LR" and "RL" compared to "LL" and "RR" like the "7 shuffles is enough" model suggests there should be.
For some reason, when I did all this analysis last year, I was mostly thinking about how to ensure my MTG decks are sufficiently shuffled. I didn't really think about the implications for card counting. However, normal riffle shuffling seems to have less bias (but still present) than the mash shuffling I looked at and I think most casinos use machines for shuffling these days.