CDG Quality Control & Process Improvement 3

Question 1

A diamond grader assigns D color to a stone that three senior graders later classify as E. This outcome is best described as:

Accepted Answer

An accuracy error with a one-grade deviation

Answer

The grade deviates from the consensus correct answer, making it an accuracy (trueness) error, not merely a repeatability issue.

Question 2

Which statistical tool is most appropriate for identifying whether two graders' color grade distributions differ significantly?

Accepted Answer

Two-sample t-test or Mann-Whitney U test

Answer

Inferential statistical tests (t-test for normal data, Mann-Whitney for non-parametric) formally test whether two graders' grade distributions are statistically different.

Question 3

In diamond QC, 'measurement system analysis' (MSA) evaluates which two primary components?

Accepted Answer

Repeatability (same grader, multiple times) and reproducibility (multiple graders)

Answer

MSA quantifies repeatability (within-appraiser variation) and reproducibility (between-appraiser variation) to determine if the grading system is reliable.

Question 4

A lab implements a policy requiring all stones above 1.00 ct to receive three independent clarity grades. What quality principle does this reflect?

Accepted Answer

Increased sample size to improve decision confidence on high-stakes items

Answer

Multiple independent assessments on high-value stones reduce the probability of a single grader error reaching the customer, improving confidence.

Question 5

Which process improvement concept is demonstrated when a grading lab restructures its workflow so graders never handle the same stone twice on the same day?

Accepted Answer

Memory-effect mitigation

Answer

Preventing a grader from re-examining a stone the same day reduces the memory effect, where recalled prior judgments bias the second grade.

(CDG) Certified Diamond Grader Practice Test

(CDG) Certified Diamond Grader Practice Test

CDG Quality Control & Process Improvement 3