Sigma unit

Sigma units from mean Fig. 1 The normal distribution. 

The application of sigma metrics for assessing analytical performance depends on measuring process variation and determining "process capability in sigma units. This approach malces use of the information on precision and accuracy that laboratories acquire initially during method vahdation studies and have available on a continuing basis from internal and external quahty control. An important... 

There are a number of problems connected with the use of the Fx values. They include (I) Four of the 14 p TaS used in the definition of Fx are estimated from other solvents thus their reliability is in doubt. (2) Of the 14 groups included in the correlation which resulted in Equation 34, five have Om and Up values which were assigned errors of 0.1 sigma units (28) and one group had and (Tp values of unknown error. (3) The determination of new F constants requires... 

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The following reagents were used potassium carbonate, methanol, chloroform (Merck, Germany), hexane (Panreac, Spain), acetyl chloride (Acros, Belgium), sucrose, Tris, EDTA, FCCP, malate, glutamate, FA-free BSA (Sigma, United States), and Hepes (MB Biomedicals, Germany). 

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The quality performance of a stream from a distillation column can be evaluated by the average impurity concentration in the stream and the distance from the nearest specification limit (DNS) compared to the standard deviation (Equation 7.1). The value of DNS is three times the process capability index, Cpk. The DNS value is easy to communicate in the number of sigma units ... 

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Tlie expected value of a random variable X is also called "the mean of X" and is often designated by p. Tlie expected value of (X-p) is called die variance of X. The positive square root of the variance is called die standard deviation. Tlie terms and a (sigma squared and sigma) represent variance and standard deviadon, respectively. Variance is a measure of the spread or dispersion of die values of the random variable about its mean value. Tlie standard deviation is also a measure of spread or dispersion. The standard deviation is expressed in die same miits as X, wliile die variance is expressed in the square of these units. 

PL activity was determined by monitoring A236 for the formation of unsaturated products released from 0.1% polygalacturonic acid (P-1879, Sigma), dissolved in 0.1 M Tris/HCl buffer, pH 8,0 supplemented with 0.1 mM CaCb. One unit of PL is the enzyme activity liberating 1 pmol of unsaturated oligoglacturonides from pectate per min at 25°C. Activities are given in mU / ml extract per min. 

Metrics for this might include number of excursions from statistical process control, but one very useful metric for controllability is process capability, or more accurately, process capability indices. Process capability compares the output of an in-control process to the specification limits by using capability indices. The comparison is made by forming the ratio of the spread between the process specifications (the specification width ) to the spread of the process values. In a six-sigma environment, this is measured by six standard deviation units for the process (the process width ). A process under control is one where almost all the measurements fall inside the specification limits. The general formula for process capability index is ... 

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