Chapter 1: Measurements

Question 1

Accuracy

Answer 1

The closeness of a test result or empirically derived value to an accepted reference value.

Question 2

Bias

Answer 2

The difference between the expected and the experimental result.

Question 3

Precision

Answer 3

The reproducibility of a series of replicate measurements obtained under comparable analytical conditions. Precision is often measured by %RSD.

Question 4

Random Error

Answer 4

An inescapable error, small in magnitude and equally positive and negative, associated with any analytical result.

Question 5

Systematic Error

Answer 5

Analytical errors that are the same every time (i.e., predictable) and that are not random.

Question 6

Grubbs Test

Answer 6

Is the suspect data point too far outside the edges of the distribution to be a legitimate data point?
-Assumes the underlying data distribution is normal.
What is the formula? (mean-questioned value)/standard deviation

Question 7

Type 1 error

Answer 7

Null hypothesis incorrectly rejected

Question 8

Type 2 error

Answer 8

Null hypothesis incorrectly accepted

Question 9

Hypothesis Testing

Answer 9

provides a statistical measure to make a decision (confidence level)

Question 10

Pedigree

Answer 10

The systems, people, and procedures that stand behind forensic chemistry testing and results.

Question 11

Metrology

Answer 11

The science of making measurements.

Question 12

What is a good measurement?

Answer 12

-One that answers the forensic question at hand and is:

-Fit for purpose
-Reasonable
-Defensible
-Falsifiable

Question 13

What is a forensic question?

Answer 13

It is the pertinent question.

-What did this person die from?
-Is this white powder a controlled substance?

Question 14

What is a legal question?

Answer 14

It is a question dealing with the law and crime.

-Does the soil in this shoe link a person to a crime scene?
-Did that person commit a crime?

Question 15

What does NUSAP mean?

Answer 15

Number
Unit
Spread
Assessment
Pedigree

Question 16

Mean

Answer 16

The average

Question 17

Standard Deviation

Answer 17

Average deviation from the mean

Sq. rt of (Xi-Xmean)^2/n-1

Where n is the sample number

Question 18

Variance

Question 19

CV or %RSD

Answer 19

standard dev/Xmean *100

Question 20

Probability distribution factor

Question 21

Confidence Interval

Question 22

Student t distribution

Question 23

Population vs sample statistics

Answer 23

Population is greater than 30

Sample applies if a subset are tested or there is any doubt about the subset being representative of the parent population