One talks about statistical significance if the observation of a population group clearly deviates from the expected value. To be able to evaluate this statistical methods are applied which compare the number of diseases observed in an examined population group with the number of the cases expected in this group, if the diseases in the observed group occurred with equal frequency - referred to the considered number of persons - as in the comparison group. As these are random samples, one cannot just say these are more or less, but for this statement one has to state an error probability. It has been agreed that a deviation between observed and expected case numbers is considered to be significant if this error probability is less than 5 %.