Uncertainty Assignment Based on Number of Available Data

Uncertainty Assignment Based on Number of Available Data 

As indicated in the Nuclear Energy Agency reviews, the assignment of an uncertainty is quite subjective. Typically, this is exacerbated by the fact that the majority of studies only quote uncertainties based on numerical treatment of the experimental data. They generally do not account for any kind of systematic error that might be involved in the experimental procedure used. Ekberg et al. (2000) included all relevant systematic errors involved in their potentiometric measurements for the determination of the hydrolysis constants of thorium(lV) and presented both the uncertainties derived as a result of the numerical treatment of the data and the total uncertainty where the systematic errors were also included. Their data showed that the total uncertainty was about a factor of 4-10 larger than that derived in the numerical treatment. 

The equation utilised to determine the total uncertainty is (Ekberg et al., 2000) 

Hydrolysis of Metal Ions, First Edition. Paul L. Brown and Christian Ekberg. 

For example, in the experiments of Ekberg et al. (2000), the systematic errors would have included those related to the measurement of pH, ionic strength, titrant concentration and volume addition, temperature, etc. Each Sj must be related to the X value and be expressed in the same units (Brown, Curti and Grambow, 2005). As indicated, the estimated total uncertainty is significantly larger than that measured from the numerical treatment. The total uncertainty is a measure of the reliability and reproducibility of the stability constant, whereas the standard deviation derived in the numerical treatment is a measure of the precision of the experiment only (Brown, Curti and Grambow, 2005). On the basis of the difference between the total uncertainty and the numerical standard deviation, the uncertainties accepted in the present review have been increased substantially from those quoted in the majority of the original studies. 

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