1. What is the Standard Deviation Index?

The Standard Deviation Index (SDI) is a statistical measure that quantifies how far a value deviates from the mean in terms of standard deviations, expressed as a percentage. It's commonly used in quality control and laboratory medicine.

2. How Does the Calculator Work?

The calculator uses the SDI formula:

Where:

• \( sd \) — Standard deviation
• \( mean \) — Mean value

Explanation: The SDI shows the standard deviation as a percentage of the mean, providing a relative measure of variability.

3. Importance of SDI Calculation

Details: SDI is crucial for assessing process variability, quality control in laboratories, and comparing measurement precision across different scales or units.

4. Using the Calculator

Tips: Enter the standard deviation and mean values in the same units. Both values must be positive, and the mean cannot be zero.

5. Frequently Asked Questions (FAQ)

Q1: What does a high SDI indicate?
A: A high SDI indicates greater variability relative to the mean, suggesting less consistency in measurements or processes.

Q2: What are typical SDI values?
A: In quality control, SDI values below 5% are generally considered excellent, while values above 15% may indicate problematic variability.

Q3: How is SDI different from CV (Coefficient of Variation)?
A: SDI and CV are essentially the same measure - both express standard deviation as a percentage of the mean.

Q4: When should SDI be used?
A: SDI is particularly useful when comparing variability across different measurement scales or when the mean values differ significantly.

Q5: Are there limitations to SDI?
A: SDI can be misleading when the mean is close to zero, as the percentage becomes very large. It's also less meaningful for non-normal distributions.