Block sampling is a sampling technique used in auditing, where a sequential series of selections is made. For example, an auditor elects to use block sampling to examine customer invoices, and intends to pick 50 invoices. She picks invoice numbers 1000 through 1049. This approach is very efficient, since a large cluster of documents can be pulled from one location. However, a more random selection method would do a better job of sampling the entire population. When using block sampling, sampling risk can be reduced by selecting a large number of blocks of samples.