How it works
Compute Q1 and Q3 with linear interpolation at positions (n−1)×0.25 and (n−1)×0.75. IQR=Q3−Q1; fences=Q1−1.5×IQR and Q3+1.5×IQR.
Input definitions
- Numeric values
- Plain text; maximum 200,000 characters.
A worked example
- Numeric values
- 1, 2, 3, 4, 5
Assumptions & limits
Type 7 quartiles, not median-of-halves. A value outside a fence is a screening flag, not proof of an error.
Sources & review
Maintained by AnsRio. Methods and examples use automated checks; this does not imply independent professional certification.
Method updated 2026-10-17. Content checked against the stated method and examples. Our verification approach.
Common questions
Does an outlier fence prove a value is wrong?
No. The 1.5×IQR fences flag unusual values for investigation. Valid observations can fall outside them, and different quartile conventions can move the fences.
Why can statistical results differ between tools?
Denominator, interpolation and boundary conventions can differ. Use the method and assumptions on this page to compare the same definition; displayed decimals may also be rounded.
How does the Interquartile range and outlier fences tool work?
Compute Q1 and Q3 with linear interpolation at positions (n−1)×0.25 and (n−1)×0.75. IQR=Q3−Q1; fences=Q1−1.5×IQR and Q3+1.5×IQR.
What are the assumptions and limits of Interquartile range and outlier fences?
Type 7 quartiles, not median-of-halves. A value outside a fence is a screening flag, not proof of an error.