| Hi LI Xue,
This is more psychological, but I think it has roots in the biology of the brain. You could try to figure out why people are convinced that they see specific numbers on clocks and other places and that those numbers are unusual or have significance. For example, some people think they see 333 or 111 everywhere they go and this means ghosts. What are the probabilities of seeing these different numbers compared to any other set of digits generated by a clock each 24 hours? Are there any reasons people would be more likely to see 333 than any other number? (I'm thinking like that kids and teachers get out of school at 3 or 3:30 and maybe they all look at the clock around that time and are more likely to notice a 3:33. When people wake up in the night, are they more susceptible to being struck by "patterns" like 111, 222, 333, 444, or 911?
What makes humans notice patterns and disregard unpatterned information.? And so on.
You could test people by suggesting that they notice certain numbers then expose them to a random series of sets of digits and see what they report "seeing." | 
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