Standard Deviation Index Calculator
Calculate SDI to measure bias between laboratory and consensus group means
Calculate Standard Deviation Index
The mean of your test/laboratory measurements
The mean of the reference/consensus group
The standard deviation of the reference/consensus group (must be > 0)
⚠️ Consensus group standard deviation cannot be zero. Please enter a positive value.
SDI Interpretation Guide
SDI = 0
Perfect agreement
0 < |SDI| ≤ 1
Acceptable performance
1 < |SDI| ≤ 1.25
Within acceptable limits
1.25 < |SDI| ≤ 1.49
May need examination
1.5 ≤ |SDI| ≤ 1.99
Marginal - examine test
|SDI| ≥ 2
Unacceptable - action required
Key Concepts
Laboratory Mean
Mean of your test measurements (sample mean)
Consensus Group Mean
Mean of the reference group (population mean)
SDI Sign
+ indicates lab > consensus, - indicates lab < consensus
Quality Control Tips
SDI measures bias in standard deviations
Target SDI is 0.0 (no bias)
Monitor trends over time
Take corrective action when |SDI| ≥ 2
Understanding Standard Deviation Index (SDI)
What is SDI?
The Standard Deviation Index (SDI) is a measurement of bias that quantifies how far your laboratory mean is from the consensus group mean, expressed in terms of the consensus group's standard deviation units.
Why Use SDI?
- •Identifies systematic bias in testing procedures
- •Provides standardized measure for comparison
- •Helps maintain quality control standards
- •Simple calculation with clear interpretation
Formula and Calculation
SDI = (Lab Mean - Consensus Mean) / Consensus Std Dev
Where each component represents the respective statistical measure
Interpretation Guidelines
Positive SDI: Laboratory mean > Consensus mean
Negative SDI: Laboratory mean < Consensus mean
Zero SDI: Perfect agreement (ideal scenario)
Magnitude: Distance in standard deviation units
SDI Categories and Actions
Excellent (SDI = 0)
Perfect agreement. Continue current procedures.
Good (|SDI| ≤ 1)
Acceptable performance with minimal bias. Monitor regularly.
Acceptable (1 < |SDI| ≤ 1.25)
Within limits but watch for trends.
Warning (1.25 < |SDI| ≤ 1.49)
Review procedures and calibration.
Alert (1.5 ≤ |SDI| < 2)
Examine test case immediately.
Critical (|SDI| ≥ 2)
Unacceptable - urgent action required.
Applications
Laboratory Quality Control
Monitor test accuracy and identify systematic errors
Proficiency Testing
Compare laboratory performance to peer groups
Method Validation
Assess accuracy of analytical methods
Process Monitoring
Track performance trends over time