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Statistical Reference Guide
Measurement systems analysis (MSA)
Trueness
Estimating the bias of a measurement system
Estimate the trueness of a measurement system or measurement procedure.
Select a cell in the dataset.
On the
Analyse-it
ribbon tab,
in the
Statistical Analyses
group,
click
Trueness
.
The analysis task pane opens.
In the
Y
drop-down list, select the measured quantity variable.
If there are multiple levels of measurement, in the
By
drop-down list, select the level variable, and then:
If the values are identifiers, select the
Identifier
check box, and then in the
Assigned values
grid, under the
Value
column alongside each level, type the value.
If the values are relative dilutions made by mixing high and low pools, select the
Relative values
check box, and then in the
Assigned values
grid, under the
Value
column for the first and last level, type the value (intermediate values are automatically calculated using relative values).
If the values are known/expected/assigned values, select the
Known values
check box.
If the reference materials package insert includes an estimate of the uncertainty of the assigned values, select the
Uncertainty in assigned values
check box, and then in the
Assigned values
grid, under the
SE
column for each level, type the value:
If the estimate is expressed as standard uncertainty or combined standard uncertainty, use the value.
If the estimate is expressed as a 95% confidence interval (CI) use the value CI/2, or if the confidence interval is expressed as upper and lower limits use the value (CI upper limit- CI lower limit)/2.
If the estimate is expressed as expanded uncertainty (U) with a coverage factor (% or k) use the value U/k. If coverage is 95%, use the value U/2; if coverage is 99%, use the value U/3.
Optional:
To compare the bias against performance requirements:
If the allowable bias is a constant or proportional value across the measuring interval, select
Across measuring interval
, and then in the
Absolute
edit box, type the bias in measurement units, and/or in the
Relative
edit box, type the bias as a percentage (suffix with % symbol).
Note:
The allowable bias is the greater of the absolute bias and the relative bias for each level. Therefore, with a absolute bias of 5mg/dL and a relative bias of 10%, the allowable bias will be set at 5mg/dL for all values 0 mg/dL up to 50mg/dL and then at 10% of assigned value for values above 50mg/dL.
If the allowable bias varies for each level, select
Each level
and then in the
Allowable bias
grid, under the
Absolute / Relative
column alongside each level, type the bias in measurement units, or the bias as a percentage (suffix with % symbol).
Note:
To compare if the value of the reference material is equal to the assigned value, see
Testing against an assigned value
.
Click
Calculate
.
Related concepts
Bias
Related tasks
Testing against an assigned value
Testing bias against allowable bias
Related reference
Dataset layout
Related information
CLSI. (2014b).
User Verification of Performance for Precision and Trueness (EP15-A3)
. Clinical and Laboratory Standards Institute.
Available in Analyse-it Editions
Method Validation edition
Ultimate edition
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Statistical Reference Guide
Distribution
Compare groups
Compare pairs
Contingency tables
Correlation and association
Principal component analysis (PCA)
Factor analysis (FA)
Item reliability
Fit model
Method comparison
Measurement systems analysis (MSA)
Precision
Trueness
Bias
Estimating the bias of a measurement system
Testing against an assigned value
Testing bias against allowable bias
Linearity
Estimating the linearity of a measurement procedure
Interferences
Detection capability
Study design
Reference interval
Diagnostic performance
Control charts
Process capability
Pareto analysis
Study Designs
Bibliography
Version 5.65
Published 14-Aug-2020
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