PRELIM LEC: Quality Assurance (BISHOP) Flashcards
ref: Lec and Lab Discussion and Chapter 3 of Bishop
The foundation for monitoring performance (known
as QC) is
descriptive statistics
This symmetrical
shape is often called a
“bell curve.”
describes many continuous laboratory variables and shares several unique characteristics
Gaussian distribution
summarizes the above relationships between the area under a Gaussian distribution and the SD
“68–95–99 Rule”
provides objective an objective measure of the line of best fit for the data
linear regression analysis
Three factors are generated in a linear regression
the slope, the y-intercept, and the
correlation coefficient (r)
An alternate approach to visualizing paired data is the difference plot, which is also known as the
Bland-Altman plot
The difference between test and reference method results is called
error
is a measure of the strength of the
relationship between the two methods
correlation coefficient (r)
There are two kinds of error measured in COM experiments:
random and systematic
is present in all measurements and can be either
positive or negative, typically a combination of both positive and negative errors on both sides of the assigned target value
Random error
influences observations consistently in one direction (higher or lower).
Systematic error
Systematic error can be further broken down into
constant error and proportional error
exists when there is a continual difference between the test method and the comparative method
values, regardless of the concentration
Constant systematic error
exists when the differences between the test
method and the comparative method values are proportional to the analyte concentration
Proportional error
are used to draw conclusions (inferences)
regarding the means or SDs of two sets of data
Inferential statistics
is the cause of lack of precision or the imprecision in a test
Random analytic error
Ability of a method to detect small quantities or
small changes in concentration of an analyte
Analytic sensitivity
Ability of a method to detect only the analyte it is
designed to determine, also known as cross-reactivity
Analytic specificity
Range of analyte that a method can quantitatively report, allowing for dilution, concentration, or other pretreatment used to extend AMR
CRR (clinically reportable range)
Also known as linear or dynamic range. Range of analyte concentrations that can be directly measured without dilution, concentration, or other pretreatment
AMR (analytic measurement range)
Lowest amount of analyte accurately detected by a method
LoD (limit of detection)
Lowest amount of analyte that can be reported while achieving a precision target (e.g., lowest concentration at which a CV of 10% may be achieved)
LoQ (limit of quantitation)
Refers to the difference between the measured value and the mean expressed as a number of SDs. An SDI = 0 indicates the value is accurate or in 100% agreement; an SDI = 3 is 3 SDs away from the target (mean) and indicates inaccuracy. SDI may be positive or negative
SDI (standard deviation index)
Dispersion of repeated measurements about the mean due to analytic error
Precision
How close the measured value is to the true value due to systematic error, which can be either constant or proportional
Accuracy
Error always in one direction (may be constant or proportional).
Systematic error
Difference between the true value and the measured value
Bias
Type of systematic error where the magnitude
changes as a percent of the analyte present, error dependent on analyte concentration.
Proportional error
Type of systematic error in the sample direction and
magnitude; the magnitude of change is constant and not dependent on the amount of analyte
Constant error
Ability of a test to detect a given disease or condition
Diagnostic sensitivity
Error varies from sample to sample. Causes include
instrument instability, temperature variations, reagent variation, handling techniques, and operator variables.
Random error
Random error plus systematic error
Total error
Standard deviation index. ((Test method value) − (Reference method value))/(Reference method SD), analogous to Z-score.
SDI
Chance of an individual having a given
disease or condition if the test is abnormal
Positive predictive value
Ability of a test to correctly identify the absence
of a given disease or condition
Diagnostic specificity
Chance an individual does not have a given
disease or condition if the test is within the reference interval
Negative predictive value
