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Data Reduction Method Explained

LGC Maine Standards uses a data reduction process that calculates the target values for each test run. The absolute and percent limit differences are calculated from the actual recovered values compared to the calculated targets. MSDRx® software (download from image below) uses simple linear regression, which means a line that fits the equation y = mx + b (where m is the ‘slope’ and b is the ‘y-intercept’), to create your unique equation for each test performed.  The statistical method used to calculate this line is called ‘least squares fit’.

Download our Free Data Reduction Software, MSDRx®

Click on image to download.

Target Value Calculation

There are many methods that can be used to calculate target values and two examples are provided in each VALIDATE® product insert.  This explanation outlines the method used when data is processed at LGC Maine Standards or when a laboratory uses our free of charge MSDRx® software (download from image above).

VALIDATE® products are manufactured to provide an equal distance (delta) between Levels 1 to 5.  Therefore, two recovered values can be held as “True” and the other level’s target values are calculated based on equal distance.

First, simple linear regression, ‘least squares fit’, is performed using the recovered values of level 1 and 3* to calculate the target values.  Appropriate equal distance values are input as the ‘x’ values and recovered values for the levels are used as ‘y’ values to calculate a regression equation.

*If non-numerical values are present for the level 1 recoveries, the software will use levels 2 and 3.

Using the equation calculated above, equal distance values of 1 to 5 are entered into the equation as ‘x’ values.  The resulting ‘y’ values are the target values.

Limits

After calculating the target values, the next step is to calculate the ‘Limits’.  The Limits are based on the Clinical Laboratory Improvement Act of 1988 (CLIA ’88) analytical limits (Total Allowable Error), if defined, and/or other published industry-accepted limits for each specific analyte.  Fifty percent of the Total Allowable Error is used for linearity limits.

The allowable limit for linearity is subtracted from the target value to establish the lower limit.  The upper limit is calculated by adding the allowable limit for linearity to the target value. This is represented by the red lines on a Validate report.

The CLIA ’88 ‘criteria for acceptable performance’ can be found on the internet in two locations:

In cases where CLIA ’88 has not defined limits of performance for a test procedure, limits are suggested that coincide with performance characteristics of a similar chemistry. 

For example, GGT does not have CLIA limits defined.  The GGT chemistry has performance characteristics similar to that of AST.  Therefore, the performance limits for AST are applied to GGT.

Questions?


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