Comprehensive Calculator Guide
This calculator finds outliers with the 1.5 × IQR rule and gives the lower and upper fences outside which a value counts as an outlier. In 12, 14, 15, 15, 16, 17, 18, 19, 45 the fences are 8.5 and 24.5, so 45 is an outlier. It explains how outliers affect the mean and what to do about them.
Tukey’s fences
Lower fence = Q1 − 1.5 × IQR; upper = Q3 + 1.5 × IQR. Don’t drop outliers automatically: fix entry or measurement errors, keep real ones, and use robust measures such as the median.
How to Use
- Enter at least four values.
- No need to sort.
- Press “Find outliers” to see them and the fences.
Formula Used
Fences: Q1 − 1.5 × IQR and Q3 + 1.5 × IQR
Practical Examples
- Example 1
- Fences 8.5 and 24.5; 45 is out.
- Example 2
- Salaries: 25,000 is out.
Important Tips
- Check each outlier’s source.
- Use the median when keeping them.
- Try z-scores for big data.
Common Mistakes to Avoid
- Deleting outliers blindly.
- Using the rule on tiny data.
- Judging by eye.
Frequently Asked Questions
- What is an outlier?
- A value beyond the fences.
- Delete it?
- Only if it is an error.
- Why 1.5?
- Tukey’s convention.