Chapter 3: Statistics and Quality Control Flashcards
Standard deviation
1 standard deviation: 68.3%
2 standard deviations: 95.4%
3 standard deviations: 99.7%
Variance
The square of the standard deviation
Coefficient of variation
Standard deviation divided by the mean x 100; measures the precision or reproducibility of the test
Sensitivity
TP / (TP + FN) x 100
Specificity
TN / (TN + FP) x 100
Accuracy
Sum of all true measurements divided by the total number of measurements x 100
Detection limit
Lowest detectable value
Trend
Indicates a gradual loss of reliability in the test system (ex: deterioration of the instrument light source, gradual accumulation of debris, aging of reagents)
Shift
Abrupt changes in the control mean (ex: sudden failure of the light source, change of reagent lot, major instrument maintenance)
Random error
Any positive or negative deviation away from the calculated mean
Rule 1 2s
A single control observation is outside the +-2s limit; indicates that random error or systematic error may be present
Rule 1 3s
Identifies unacceptable random error or the beginning of a large systematic error
Rule 2 2s
Two consecutive QC results greater than 2s on the same side of the mean; within: systematic error
Rule R4s
Is there is a 4s difference between control values within a single run, it indicates random error
Rule 3 1s
Three consecutive results greater than 1s on the same side of the mean; can be analytic bias or small systematic error; within: systematic bias, across: systematic error
Rule 4 1s
Four consecutive results greater than 1s on the same side of the mean; can be analytic bias or small systematic error; within: systematic bias, across: systematic error
Rule 7x 8x 9x 10x 12x
When there are 7, 8, 9, 10, or 12 control results on the same side of the mean regardless of where they are located; within: systematic bias, across; systematic bias over a broader concentration
