Division 2.1: TREATMENT OF RESULTS - Commission Regulation (EC) No 761/2009 of 23 July 2009 amending, for the purpose of its adaptation to technical progress, Regulation (EC) No 440/2008 laying down test methods pursuant to Regulation (EC) No 1907/2006 of the European Parliament and of the Council on the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) (Text with EEA relevance)

Fibre diameters do not usually have a normal distribution. However, by performing a log transformation it is possible to obtain a distribution that approximates to normal.

Calculate the arithmetic mean (mean lnD) and the standard deviation (SD_lnD) of the log to base e values (lnD) of the n fibre diameters (D).

$mean lnD = \frac{ΣlnD}{n}$	(1)
${SD}_{lnD} = \sqrt{\frac{{Σ(lnD – mean lnD)}^{2}}{n – 1}}$	(2)

The standard deviation is divided by the square root of the number of measurements (n) to obtain the standard error (SE_lnD).

{SE}_{lnD} = \frac{SD}{\sqrt{n}} n

(3)

Subtract two times the standard error from the mean and calculate the exponential of this value (mean minus two standard errors) to give the geometric mean minus two geometric standard errors.

{LWGMD – 2SE = e}^{{(mean lnD – 2SE}_{lnd})}

(4)

Division 2.1 TREATMENT OF RESULTS