QC Statistics Flashcards
Define standard deviation
A measure of the spread or variability in a data set
What is a reference range
Range of values that includes 95% if the test results for healthy reference population
How many stdevs are in a 95% confidence interval
+/- 2
What does having a confidence interval of 95% mean
Where 95% confident the true value is in range
Accounts for unavoidable error caused by sampling variability and imprecision
What is coefficient of variation
used to compre the stdev of two samples for same analyte
How do you calculate %CV
=(stdev*100)/mean
How does %CV interpretation affect results
Low percentage= less spread/variability => higher precision
Define CVR
Coefficient of variation ratio
determines if your labs precision is acceptable compared to other lab given same instrument and reagents
What other statistical test is used for precision
F test: analysis of variance
What other test is used for accuracy
Paired t test
How is control range determined
assay of controls with regular batch of assays for 15-25 days where controls are treated as specimens
Resultant mean and sd form a levey-Jennings chart
What are levy-Jennings charts
Charts to evaluate unacceptable runs and maintain stability of analytical measurement system to detect changes in said system
Define a shift
A sudden and sustained change in one direction in control sample values
Malfunction of instrument
Define Trend
A gradual change in control sample results
Progressive problem with test system
Define dispersion
Imprecision, random error or lack of precision increases
Instability problems
