Stats and Lab Management

Question 1

Coefficient of Variation (CV)

Answer 1

Coefficient of Variation (CV)

CV=SD/mean x 100

• describes standard deviation as a percentage of the mean
• since the CV is a function of the mean, it refers to the precision at a particular analyte concentration
• generally, CV increases as the analyte increases
• assess test performance at critical cut-off values

Question 2

Sensitivity

Answer 2

Sensitivity = TP/(TP+FN)

Question 3

Specificity

Answer 3

Specificity = TN/(TN+FP)

Question 4

Positive Predictive Value

Answer 4

Positive Predictive Value

PPV=TP/(TP+FP)

• when disease prevalence is low, the PPV of a test declines and the NPV increases
• when disease prevalence is high, the PPV of a test increases and the NPV decreases

Question 5

Negative Predictive Value

Answer 5

Negative Predictive Value

NPV=TN/(TN+FN)

• when disease prevalence is low, the NPV of a test increases and the PPV decreases
• when disease prevalence is high, the NPV of a test decreases and the PPV increases

Question 6

Relative Risk

Answer 6

Relative risk

• the risk of an outcome ‘y’ in the presence of condition ‘x’ as compared to the population
• smokers (x) who develop cancer (y) vs. general population

RR=(#smokers who dev cancer/#smokers)/(#population who develop cancer/#population)