Bitcoin Block confirmations, Why do they lag at times?

[mikeywith]

@fillippone, you brought up a very interesting point, one of the main reasons why miners would mine empty blocks is what you mentioned about the "transactions of the last/previous block", validating the transactions of the previous block can take some time probably 10-20 seconds, large blocks may take over 20 seconds to validate, miners pay a ton of money during those 20 seconds, and if they happen to solve the puzzle before they were done with validating the transactions they would broadcast an empty block to avoid invalidation, however, since every hash is independent from every other hash, they lose nothing by including transactions ONCE they have verified them, but if they happen to solve the block BEFORE that, i don't see why would anyone refer to them as selfish miners, of course ignoring spy mining I see no economical benefit of purposely mining an empty block.

I don't think empty blocks are exactly bad, and assuming the average validation time is 15 seconds, it's safe to assume that empty blocks have a probability of 1-exp(-1/600) - 1-exp(-15/600) = 2.3% or every 43 blocks / 3 times a day, as long as we are not way above that, I think we are good.