Table A13: Extracted precision data 11
|Sample||% of mean of pair|
|Standard deviation (%)||6.6||4.3||4.9|
|95% error (%) 12||5.5||3.6||4.1|
|Guideline value (mg/kg)||30||370||300|
|Lower than guideline value: any value below (mg/kg) ... 13||28.4||356.7||287.6|
|Higher than guideline: any value above (mg/kg) ...||31.6||383.3||312.4|
|Indistinguishable from guideline (mg/kg)||28.4 to 31.6||357 to 383||287 to 312|
Back to footnote reference 11 This method assumes that samples themselves were replicated at each location, so that the variation measured represents the sum of analytical and sampling variation.
Back to footnote reference 12 The samples taken are not the site, but they do represent it. Student's t-test 95% error is the best method to establish whether or not we can say that the underlying population mean for the site (that a given sample was collected from) is distinguishable from the guideline value. Normality can be assumed as data here describe variation between the normalised replicates.
Back to footnote reference 13 Example for arsenic: calculated as 30 mg/kg minus 5.5% of 30 mg/kg.