-
errors that occur in testing process may be either
-
only a cause for rejection of the test run if it exceeds +2SD
random error
-
error is not acceptable, as it indicates some failure in the system that can and should be corrected
systematic error
-
examples of systematic error
-
when the control is on the same side of the mean for five consecutive runs
shift
-
when the control is moving in one direction, and appears to be heading toward an out of control value
trend
-
can help distinguish between normal variation and systematic error
levey-jennings charts
-
in most situations, measurement uncertainty is estimated at
95% coverage
-
for most instances, a range of ___ is accepted as measurement uncertainty that is explained by random variation
± 2SD
-
when QC sample that is used in a test run is out of the acceptable range, the run is considered to be ___________
out of control
-
the closeness of a measurement to its true value
accuracy
-
the amount of variation in the measurements
precision
-
the difference between the expectation of a test result and an acceptable reference method
bias
-
the reliability of a method is judged in terms of
accuracy and precision
-
to determine acceptable variation, the laboratory must compute the SD of the ___ values
20
-
____ of the values will fall within -1SD and +1SD of the mean
68.3%
-
____ of the values will fall within -2SD and +2SD of the mean
95.5%
-
____ of the values will fall within -3SD and +3SD of the mean
99.7%
-
the measurement of variation in a set of results
standard deviation (SD)
-
-
when only one control is used, we consider an examination run to be __ if a value is within 2SD of the mean
in control
-
the SD expressed as a percentage of the mean
coefficient of variation (CV)
-
formula CV
- CV (%) = SD x 100
- ------
- Mean
-
used to monitor precision
CV
-
ideally, the value of CV should be
less than 5%
-
westgard rule was developed by
James Westgard
-
multirule system requires running two controls (or 3 controls) of different target values for each set of examinations, developing a Levey-Jennings chart for each, and applying the rules
Westgard Rules
-
represent the range graphically for purpose of daily monitoring
Levey-Jennings Chart
-
another set of rules used to avoid rejecting runs that may be acceptable
Westgard Rule
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