Each monitoring scheme implements data quality control at the national level. PECBMS facilitates contacts between the schemes to share experience and provides suggestions on good practice as by publishing the Best Practice Guide (Voříšek et al., 2008). Coordinators of national schemes ensure that their fieldworkers are sufficiently trained and skilled. Some schemes even test the knowledge and identification skills of field workers, for instance, in Norway. Many schemes provide fieldworkers with identification tools (e.g. records of bird songs and calls), maps and field recording sheets, including detailed instructions.
The data collected by field workers are examined once received, suspicious records are usually checked immediately, and if not justified, they are abolished. Automatic tools (e.g. automatic warning signals issued when suspicious data are entered into a database) are of increasing importance, especially in on-line data collation, e.g. to prevent typing errors. National schemes also check the data quality at the data analysis level, for instance, by setting filters for a minimum amount of record/sites counted, etc.
Most importantly, countries have implemented standardized procedures for fieldwork and produce national indices and trends in the same way.