Laboratory Quality, Statistics & Interpretation
Every laboratory quality, statistics & interpretation calculator on CalcEngines — unit converters, derived indices and interpretive tools, each with its formula, a worked example and the reference intervals it is judged against.
24 calculators in this section
- Bland-Altman Limits of Agreement CalculatorTurn a mean difference and the scatter around it into limits of agreement, with a confidence interval for the limits themselves — and see why a correlation coefficient of 0.99 tells you nothing about whether two methods agree.
- Carryover Test InterpreterRun high samples, then low ones, and see whether the first low result is pulled up by the high ones that preceded it. The arithmetic is easy; the hard part is what to compare it against. This page applies two criteria — is the difference bigger than the noise, and is it bigger than the difference that would change a decision — because a carryover coefficient of a twentieth of a per cent can be clinically catastrophic when the dynamic range is wide.
- Coefficient of Variation CalculatorTurn an SD and a mean into a CV%, and compare it with the target you are working to. An SD on its own is meaningless — the CV is what makes imprecision comparable between analytes and between levels.
- Cohen’s Kappa CalculatorAgreement between two observers, corrected for the agreement chance alone would have produced. Enter a 2×2 table and read κ beside the raw agreement it came from — because with skewed marginals those two numbers tell opposite stories.
- Delta Check CalculatorThe change between a patient's current result and their previous one, absolute and proportional, against the time between them — and against limits only your own laboratory can set.
- Deming Regression CalculatorThe regression for comparing two assays, where both axes carry measurement error. Ordinary least squares assumes the comparative method is exact, and systematically under-estimates the slope when it is not.
- Diagnostic Odds Ratio CalculatorCollapse a test's whole performance into one number for comparing tests and pooling studies — then see why that number is the wrong tool at the bedside.
- Haemolysis, Icterus & Lipaemia InterpreterA haemolysis, icterus or lipaemia index is not a number you can look up a threshold for. The units are manufacturer-specific and do not transfer between platforms, and the concentration at which interference becomes clinically significant is different for every analyte — potassium and LDH fail at a degree of haemolysis that troponin tolerates. So this page asks for your laboratory's own alert and hold indices for the analyte in question, and then tells you which way the result is wrong and what the comment should say.
- Likelihood Ratio CalculatorTurn sensitivity and specificity into LR+ and LR−, then apply one to the probability you already had. Likelihood ratios are the only test property that combines directly with a pre-test probability.
- Limit of Blank, Detection and Quantitation CalculatorCompute LoB and LoD the way CLSI EP17 defines them, from blank and low-level imprecision — and find out why the limit of quantitation is not a formula at all.
- Linearity Verification InterpreterYou ran a dilution series and one level sits off the straight line. CLSI EP06-Ed2 does not ask whether that deviation is statistically significant — it asks whether it is bigger than the deviation you decided in advance you could tolerate. This page applies that comparison, and then answers the question that actually follows: can the measuring interval be truncated, or is the method nonlinear inside it? For the fit itself, see the Deming regression calculator.
- Measurement Uncertainty CalculatorCombine within-laboratory imprecision and the uncertainty of the bias estimate into a combined standard uncertainty, then expand it to the coverage interval ISO 15189 expects you to be able to quote.
- Method Comparison Acceptance InterpreterThis page does not fit a regression. It consumes one. Give it the slope and intercept you already have from the Deming regression calculator, the concentrations where a clinical decision actually gets made, and the error you are allowed — and it answers the question CLSI EP09c-Ed3 asks: is the predicted bias at each medical decision point acceptable? A slope of 1.05 is not a verdict; a 5% bias at a threshold that separates treating from not treating might be.
- Precision Verification InterpreterYour five-day precision study came out higher than the manufacturer's claim. That is not the same as failing it. CLSI EP15-A3 compares the observed SD against an upper verification limit built from the claim and the degrees of freedom, because a small study will exceed a true claim by chance about half the time. This page applies that comparison to both components at once, and tells you which one failed — which is the part that says where to look.
- Proficiency Testing Failure InterpreterAn EQA sample has come back outside the acceptance limit. Before you touch the instrument, answer four questions: did one analyte fail or many, were the deviations all in one direction or scattered, was the internal quality control acceptable at the time, and was the sample handled exactly like a patient sample? Those four answers separate a bias from an imprecision problem from a blunder, and those are three different investigations.
- Reference Change Value CalculatorHow much must a result move before the change is real? The reference change value combines analytical imprecision with within-subject biological variation to answer the question every repeat test raises.
- Reference Interval Verification CalculatorApply the CLSI EP28 verification procedure. Test twenty reference individuals against a published or manufacturer's interval, count how many fall outside, and find out whether you may adopt it.
- Sensitivity & Specificity CalculatorWork out sensitivity, specificity, PPV, NPV, accuracy and prevalence from a 2×2 table — and see why the first two belong to the test and the next two belong to the population you applied it to.
- Sigma Metric CalculatorCombine allowable total error, bias and imprecision into a single figure for how much room a method has — and let that figure decide how many controls you run and which rules you apply.
- Standard Deviation Index CalculatorPlace an external quality assessment result against its peer group in standard deviations. The SDI measures bias against your peers — which is not the same thing as bias against the truth.
- Total Analytical Error CalculatorCombine bias and imprecision into one figure for the worst a result is likely to be wrong by, then compare it with the total error your method is allowed.
- Westgard Rules InterpreterEnter this run's control result as a standard deviation index and answer five questions about the recent history. The page names the Westgard rule violated and says whether the run should be rejected.
- Wilson Confidence Interval CalculatorThe confidence interval to use when a laboratory validates a qualitative method on a modest number of samples — and the one the textbook normal approximation gets badly wrong.
- Youden Index CalculatorOne number for how far a test's operating point sits above pure chance — and the reason maximising it is usually the wrong way to choose a laboratory cut-off.