Continuing with the scenario above, the police chief says that he will hire someone to tally all 8,322 tickets to prove you are wrong and that there is no bias is how tickets are issued. You want to be at least 95% confident that the error margin around your sample of 560 tickets is such that even the low end is well above 20%. So you think of it as being like a survey of 560 randomly selected drivers. Use the formula for sampling error margin to calculate the error margin for this sample.