Statistical methods

In NSVOK, the Robust Algorithm is applied for statistical comparison:

(reference ISO 13528:2005(E) - Annex C (Robust analysis)

Determination of starting median

x* = median of xi (i = 1, 2, ..., p)

An initial standard deviation is determined

s* = 1.483 median of |xi − x *| (i = 1, 2, ..., p). ϭ=s*.1.5

Remove grossly erroneous results

For each measured value

(xi): > max xi=( x* + ϭ) are equated to max

xi < min xi=( x* - ϭ) are equated to min xi

With these values of xi are calculated

x* = Σ xi/n

s* = 1.134 √ [ 1/(n-1) * Σ (xi - x*) ]

The new s* thus obtained is multiplied by 1.5 to obtain the new ϭ


The calculation is repeated with the new values of max xi and min xi , until the first three digits of x* and s* become the same as those of the previous calculation.

The resulting values are:

x* = target value(X)

s* = SD

Each participant's z-score, CV% and D% are calculated based on their measured values.

z-score(SDI) = [X-x]/SD

CV% = SD*100/X

D% = 100*[(x-X)]X