Lab Statistics and Quality Control

Question 1

Sensitivity *

Answer 1

Probability of classifying a diseased patient as diseased.

True pos / (True pos + False negs) * 100

Question 2

Specificity *

Answer 2

Probability of classifying a Neg patient as Neg

True Negs / (True Negs + False Pos’s) *100

Question 3

Positive Predictive Value *

Answer 3

True Pos / (True Pos + False Pos) * 100

Question 4

Negative Predictive value *

Answer 4

True Neg / (True Neg + False Neg) * 100

Question 5

False Positive Rate *

Answer 5

False Pos / Total Neg Patients * 100
Probability of incorrectly classifying a non-diseased person as diseased

Question 6

False Negative Rate *

Answer 6

False Neg / Total Pos Patients * 100
Probability of incorrectly classifying a diseased person as not diseased

Question 7

Accuracy *

Answer 7

Closeness of measured values to the true value.
Ability to get close to the bullseye.

Question 8

Precision *

Answer 8

Closeness of repeated measurements to each other.
Ability to hit the same spot on the target.

Question 9

68.26% *

Answer 9

Percentage of values that will fall within one SD

Question 10

95.46% *

Answer 10

Percentage of values that will fall within 2SD

Question 11

99.73% *

Answer 11

Percentage of values that will fall within 3SD

Question 12

Mean *

Answer 12

Sum of values / # of values

Question 13

Median *

Answer 13

The value in the middle of a list

Question 14

Mode *

Answer 14

The most commonly occurring value in the set

Question 15

Unimodal Symmetrical *

Answer 15

Normal distribution, mean mode and median stack on top of each other

Question 16

Unimodal Skewed *

Answer 16

when the most frequent occurrences are higher or lower than the median (middle data) and mean (average) of the data set.

Question 17

Bimodal *

Answer 17

When there are two frequent data points, as in test results for men and women.

Question 18

Standard Deviation Definition *

Answer 18

Numerical value describing how widely points vary from the Mean.

Question 19

SD formula *

Answer 19

Square root of the Variance (sum of (X - Mean) squared) / (n-1)

Question 20

What is the Z-Score

Answer 20

Tells how many SD’s a control is from the mean. = (Control result - Mean) / SD

Question 21

Variance *

Answer 21

= (sum of (X - Mean) squared) / (n-1)

Question 22

Coefficient of Variation Definition *

Answer 22

Ratio of the Standard Deviation to the Mean

Question 23

CV formula *

Answer 23

(SD/Mean) *100

Question 24

Confidence Interval

Answer 24

A range of values calculated from the Mean and SD

Question 25

CI Formula

Answer 25

Mean +/- 2SD

Question 26

CI Formula

Answer 26

Mean +/- 2SD

Question 27

t-test

Answer 27

How significant the differences between two groups are. How likely the differences could have happened by chance.

Question 28

What are 3 types of t-test?

Answer 28

1. Independent sample t-test (compares the mean for 2 groups)
2. Paired sample t-test (compares a group of samples collected at different times)
3. One sample t-test (compares the mean of a group against a known Mean)

Question 29

Low p-values indicate

Answer 29

Your data did not happen by chance. p-value of .01 means there is a 1% probability that your results happened by chance.

Question 30

What are the four types of Error? *

Answer 30

1. Random Error (due to chance)
2. Systematic error (influences values in one direction)
3. Active Error (occurs between a specific tech and the samples)
4. Latent Error (related to the organization of the laboratory)

Question 31

Reference Range

Answer 31

Range of Normal values for a test, usually +/- 2SD or 95% confidence

Question 32

Chain of Custody

Answer 32

Chronological documentation or paper trail of a specimen throughout collection and testing. Required for any specimen used as legal evidence in court.

Question 33

Levey-Jennings Plots *

Answer 33

Plot of control results on Y-axis versus time on the X-axis

Question 34

Trend *

Answer 34

Progressive GRADUAL drift of values from a prior mean (gradual deterioration of a light source, control materials, chamber temp, or inst. calibration)

Question 35

Shift *

Answer 35

ABRUPT changes in the control mean (sudden change in light source, incubation temp, reagent lot, control integrity)

Question 36

Dispersion *

Answer 36

Lack of precision or RANDOM errors caused by inconsistent technique or stability issues (fluctuations in voltage, different techs, clots or bubbles)

Question 37

Cusum Plots *

Answer 37

Cumulative Sum Plot, used for SYSTEMATIC errors. The known value is subtracted from the measured value for each day of measurement. Difference is summed together over time. (When control data is scattered around the mean, the Cusum will wander above and below the mean yielding a relatively horizontal line)

Question 38

Westgard Rules *

Answer 38

Used for RANDOM and SYSTEMATIC errors. A set of 5 rules on whether to accept or reject a run. Based on how many times the control falls outside of the 1, 2, or 3SD’s of the mean.

Question 39

If a control was 1 2S, would you reject the run? *

Answer 39

No, run is in control

Question 40

If a control was 1 3S, would you reject the run? *

Answer 40

Yes, run is out of control

Question 41

If a control was 2 2S, would you reject the run? *

Answer 41

Yes, run is out of control

Question 42

If a control was R 4S, would you reject the run *

Answer 42

Yes, run is out of control. One value +2SD and one value -2SD

Question 43

If a control was 4 1S, would you reject the run *

Answer 43

Yes, run is out of control. Four consecutive values exceed 1SD

Question 44

If a control was 10 X, would you reject the run *

Answer 44

Yes, run is out of control. Ten values in a row above or below the mean

Question 45

Six Sigma *

Answer 45

A quality improvement process to identify and remove causes of defects and reduce errors to 3.4 defects per million tests or 6SD.

Question 46

What is the DMAIC method for Six Sigma? *

Answer 46

Define, Measure, Analyze, Improve, Control