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Standard Deviation Index Calculator

Free SDI calculator for lab EQA. Compute Standard Deviation Index, running SDI, multi-analyte SDI. C

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Why This Statistical Analysis Matters

Why: Statistical calculator for analysis.

How: Enter inputs and compute results.

SDI
LAB PROFICIENCYCLIA / CAP

Standard Deviation Index โ€” Lab Proficiency Testing

SDI for EQA. Single event, running SDI across events, multi-analyte panels. CLIA/CAP interpretation.

Z-Score โ†’Control Charts โ†’

Real-World Scenarios โ€” Click to Load

Mode

Single Event Data

Use Target + Allowable SD
sdi_results.sh
CALCULATED
SDI
0.7143
Interpretation
Acceptable
Bias%
3.16%
Sigma
2.28
Share:
SDI Result
SDI = 0.714
Acceptable
Bias%: 3.16% | Sigma: 2.28
numbervibe.com/calculators/statistics/standard-deviation-index-calculator

SDI Scale (-3 to +3)

Calculation Breakdown

COMPUTATION
SDI Formula
(Lab โˆ’ Group Mean) / Group SD
SDI
0.7143
(98 โˆ’ 95) / 4.2
CLIA/CAP
Interpretation
Acceptable
Bias%
3.16%
((Lab โˆ’ Target) / Target) ร— 100
Sigma metric
2.28
(TEa% โˆ’ |Bias%|) / CV%

For educational and informational purposes only. Verify with a qualified professional.

Key Takeaways

  • SDI: SDI = (Lab Value โˆ’ Group Mean) / Group SD. Measures how far a lab result is from the consensus mean in EQA.
  • CLIA/CAP interpretation: |SDI| โ‰ค 1.0 acceptable; 1.0โ€“1.5 warning; 1.5โ€“2.0 poor; > 2.0 unacceptable.
  • Running SDI: Track SDI across multiple survey events to detect persistent bias.
  • Bias%: ((Lab โˆ’ Target) / Target) ร— 100. Sigma metric: (TEa% โˆ’ |Bias%|) / CV%.

SDI Formula

Standard: SDI = (Lab Value โˆ’ Group Mean) / Group SD

Target-based: SDI = (Lab Value โˆ’ Target) / Allowable SD

Interpretation (CLIA/CAP)

|SDI|Interpretation
โ‰ค 1.0Acceptable
1.0 โ€“ 1.5Warning
1.5 โ€“ 2.0Poor (action required)
> 2.0Unacceptable

FAQ

What is SDI used for?

SDI is used in external quality assessment (EQA) and proficiency testing to compare a lab's result to the group consensus.

When is |SDI| > 2 unacceptable?

Per CLIA/CAP guidelines, |SDI| > 2.0 indicates unacceptable performance. The lab should investigate and correct.

SDI vs Z-score?

SDI and Z-score use the same formula when Group Mean and Group SD are the reference values.

Disclaimer: For educational purposes. Clinical labs should follow accrediting body guidelines.

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