Chapter 3: Statistics and Quality Control

Question 1

Standard deviation

Answer 1

1 standard deviation: 68.3%
2 standard deviations: 95.4%
3 standard deviations: 99.7%

Question 2

Variance

Answer 2

The square of the standard deviation

Question 3

Coefficient of variation

Answer 3

Standard deviation divided by the mean x 100; measures the precision or reproducibility of the test

Question 4

Sensitivity

Answer 4

TP / (TP + FN) x 100

Question 5

Specificity

Answer 5

TN / (TN + FP) x 100

Question 6

Accuracy

Answer 6

Sum of all true measurements divided by the total number of measurements x 100

Question 7

Detection limit

Answer 7

Lowest detectable value

Question 8

Trend

Answer 8

Indicates a gradual loss of reliability in the test system (ex: deterioration of the instrument light source, gradual accumulation of debris, aging of reagents)

Question 9

Shift

Answer 9

Abrupt changes in the control mean (ex: sudden failure of the light source, change of reagent lot, major instrument maintenance)

Question 10

Random error

Answer 10

Any positive or negative deviation away from the calculated mean

Question 11

Rule 1 2s

Answer 11

A single control observation is outside the +-2s limit; indicates that random error or systematic error may be present

Question 12

Rule 1 3s

Answer 12

Identifies unacceptable random error or the beginning of a large systematic error

Question 13

Rule 2 2s

Answer 13

Two consecutive QC results greater than 2s on the same side of the mean; within: systematic error

Question 14

Rule R4s

Answer 14

Is there is a 4s difference between control values within a single run, it indicates random error

Question 15

Rule 3 1s

Answer 15

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

Question 16

Rule 4 1s

Answer 16

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

Question 17

Rule 7x 8x 9x 10x 12x

Answer 17

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