
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
leveyjennings 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 LeveyJennings chart for each, and applying the rules
Westgard Rules

represent the range graphically for purpose of daily monitoring
LeveyJennings Chart

another set of rules used to avoid rejecting runs that may be acceptable
Westgard Rule

