Laboratory Mathematics and Calculations Flashcards

What is the mean of the control values 4, 6, 8, 10, and 12?

Answer: 8

The sum is 40, and 40 ÷ 5 values = 8.

A control has a mean of 100 mg/dL and a standard deviation of 5 mg/dL. What is the coefficient of variation?

Answer: 5%

CV = (SD / mean) × 100 = (5/100) × 100 = 5%.

Two consecutive control values exceed the same +2 SD limit. Which Westgard rule is violated and what type of error is indicated?

Answer: 2-2s, systematic error

The 2-2s rule detects systematic error when two consecutive controls exceed the same 2 SD limit.

In one run, the level 1 control is at +2.5 SD and the level 2 control is at -2.0 SD. Which rule is violated?

Answer: R-4s

R-4s is violated when the range between two controls within a run exceeds 4 SD, indicating random error.

In a Gaussian distribution, approximately what percentage of control values fall within ±2 SD of the mean?

Answer: 95%

About 95% (95.5%) of values lie within ±2 SD of the mean.

A test identifies 90 true positives and misses 10 diseased patients (false negatives). What is its sensitivity?

Answer: 90%

Sensitivity = TP / (TP + FN) = 90/100 = 90%.

A test produces 80 true positives and 20 false positives. What is the positive predictive value?

Answer: 80%

PPV = TP / (TP + FP) = 80/100 = 80%.