Laboratory statistics Flashcards
Average or arithmetic mean of a data set
Mean (𝒙̅)
Midpoint of a data set after rank-ordering the values
Median
Most frequently occurring value in a data set
Mode
Formula for standard deviation
Standard deviation (s) is the square root of variance.
Term for the square of the standard deviation
Variance (s²)
Best indicator of precision in a data set
Coefficient of Variation, which should be <10%.
Difference between the highest and lowest values in a data set
Range
In a Gaussian/Normal distribution, how are data points distributed?
Symmetrically around the mean in a bell-shaped curve.
In a Gaussian distribution, what are the relationships between the mean, median, and mode?
They are identical.
Rule that describes the distribution of data points in a normal distribution
Empirical rule: 68% ±1s, 95% ±2s, 99.7% ±3s.
Pair of medical decision points that span the limits of results expected for a healthy population.
Reference interval
Requires at least 20 study individuals; adopted if <10% (1-2 out of 20) fall outside the range.
Verifying a reference interval
Establishing a reference interval required number of study individuals
At least 120
Reference interval establishment should have a confidence interval of:
0.95
First step in method evaluation; usually done by running two control materials twice a day over a 10-day period.
Precision study
Involves spiking a sample with a known amount of an analyte and determining how much of it can be detected by the method in the presence of other compounds in the matrix.
Recovery study
Compares the means of two groups of data or the accuracy of two methods.
t test
Compares the SD of two groups of data or the precision of two procedures.
F test
Used to compare two methods using the best fit line through the data points.
Linear regression
Independent variable/ref method in linear regression.
x (VOYD)
Dependent variable/new method in linear regression.
y (VOYD)
Ability of a method to detect the smallest concentration of an analyte.
Analytical sensitivity (screening test)
Ability of a method to detect only the analyte of interest.
Analytical specificity (confirmatory)
Ability of a test to detect a given disease or condition; proportion of individuals with the disease who have a positive test result.
Diagnostic sensitivity
Ability of a test to detect the absence of a given disease or condition; proportion of individuals with no disease who have a negative test result.
Diagnostic specificity
Probability that a positive test result indicates disease; proportion of individuals with a positive result who truly have the disease.
Positive predictive value
Probability that a negative test result indicates absence of disease; proportion of individuals with a negative result who truly do not have the disease.
Negative predictive value
