In statistics and especially numeric data, statistical error is any deviation in sample data from the population of interest based on: data collection methods; and sources of data. Error related to sample selection is a source of inaccuracy, some of which can be part of the normal, random fluctuation of sample variance or it can be systematic demonstrating a pattern. Random sampling error occurs when the sample selected is an imperfect representation of the target population. The differences between the sample and population do not demonstrate a pattern, but are inherently random. Sampling error that demonstrates a pattern in the data is called systematic sampling error. A particular type of coverage error is sampling frame error, which is the difference between the actual target population and population as defined by the sampling frame. Nonsampling random error results from sources other than those ascribed to sampling.