1. What is the Peer SDI Calculation?

The Peer Standard Deviation Index (SDI) is a statistical measure that compares an observed value to a peer group's mean and standard deviation. It shows how many standard deviations an observation is from the peer mean.

2. How Does the Calculator Work?

The calculator uses the SDI equation:

Where:

• \( Observed \) — The value you want to evaluate
• \( Peer\ Mean \) — The average value of the peer group
• \( Peer\ SD \) — The standard deviation of the peer group

Explanation: A positive SDI indicates the observed value is above the peer mean, while a negative SDI indicates it's below. The magnitude shows how far from the mean in standard deviation units.

3. Importance of SDI Calculation

Details: SDI is widely used in quality control, laboratory testing, and performance benchmarking to identify outliers and assess relative performance against peer groups.

4. Using the Calculator

Tips: Enter the observed value, peer group mean, and peer group standard deviation. The peer SD must be greater than zero for valid calculation.

5. Frequently Asked Questions (FAQ)

Q1: What does an SDI of 1.0 mean?
A: An SDI of 1.0 means the observed value is 1 standard deviation above the peer mean.

Q2: What is considered a significant SDI?
A: Typically, SDI values beyond ±2.0 are considered significant deviations from the peer group.

Q3: Can SDI be used for small sample sizes?
A: SDI is most reliable with larger peer groups (n > 30). For small groups, consider using modified z-scores.

Q4: How is this different from z-score?
A: SDI is essentially a z-score when calculated against a true population, but the term SDI is often used when comparing to a peer group sample.

Q5: What if my peer SD is zero?
A: SDI cannot be calculated when peer SD is zero as it would involve division by zero. This suggests all peer values are identical.