1. www.oxforddictionaries.com
2. ISO/IEC 17043:2010, Conformity assessment—general requirements for proficiency testing
3. www.eqalm.org/site/event/Symposium2013.php , Scoring systems for qualitative schemes—response to a questionnaire
4. www.erndim.org , Performance assessment in ERNDIM proficiency schemes
5. ISO 13528:2005 Statistical methods for use in proficiency testing by interlaboratory comparisons