DIN CEN/TS 14773:2004-12

This document specifies methods for measuring the level of loss and substantial delay, using a survey of test letters, of domestic and cross-border priority and first class single piece letter mail, collected, processed and distributed by postal service operators. It is impossible in practice to distinguish between items which will never arrive and items which have been delayed for a very long time. A minimum period is therefore defined after which an item that has been sent shall be treated as if it has been lost or substantially delayed for the purposes of measurement. The resulting overall figure for loss and substantial delay is to be expressed as a percentage of the total posted priority and first class single piece mail. This indicator does not measure the postal operator's overall performance in a way which provides direct comparison of postal service operators, and does not include other service performance indicators other than those related to loss and substantial delay. According to this document, loss and substantial delay is estimated within specified accuracy limits. When the level of loss is very small it may only be possible to estimate an upper limit for the level of loss.