## Missing uncertainties

Sometimes uncertainties are not reported with the concentration measurements, usually when the data were submitted before the reporting of uncertainties became mandatory. In such cases, the uncertainties are estimated using fixed and relative standard deviations derived from the uncertainties that have been reported to the ICES data base (extraction date: 15 February 2019).

Suppose $$c$$ is a concentration reported with missing uncertainty. Then the uncertainty $$u$$ is estimated from:

$u^2 = s^2 + v^2 c^2$

where:

• $$s$$ is the fixed standard deviation, taken to be one third of the detection limit when reported, and otherwise the value estimated from the uncertainties in the ICES database
• $$v$$ is the relative standard deviation, estimated from the uncertainties in the ICES database