How to use the Outlier Detector (IQR Method)
- 1. Paste the dataEnter your numbers separated by commas, spaces or new lines.
- 2. Pick the multiplierKeep 1.5 for standard outliers or use 3 for only extreme ones.
- 3. Review the outliersSee which values were flagged and copy the cleaned list.
The IQR rule
Tukey's method marks a value as an outlier if it is below Q1 − k × IQR or above Q3 + k × IQR, where IQR = Q3 − Q1 and k is usually 1.5. Because quartiles ignore the extremes, one huge value cannot hide itself by inflating the spread, which is a weakness of the mean ± 3 SD rule.
Worked example (the default data, 15 values with one typo of 100): Q1 = 11.5, Q3 = 13.5 and IQR = 2. The fences are 11.5 − 3 = 8.5 and 13.5 + 3 = 16.5, so only 100 is flagged. Removing it moves the mean from 18.07 to 12.21, which shows how much a single bad value can distort an average.
What to do with outliers
- Check for errors first. Typos, wrong units or test records should be fixed or removed.
- Keep genuine extremes when they are real events, such as a big order or a fraud case; they may be the most important rows.
- Use robust statistics like the median and IQR when you must keep the outliers.
- Document it. Note how many rows you removed and why.
Quartiles here use the inclusive method, the same as Excel QUARTILE.INC and NumPy's default, so fences match pandas code such as df.quantile([.25, .75]). Other quartile methods can shift the fences slightly on small data sets; compare them in the quartile calculator. To see outliers as dots on a chart, use the box plot maker.
Frequently asked questions
Why 1.5 times the IQR?
It is John Tukey's convention. For normal data it flags roughly 0.7% of values, which balances catching problems against false alarms.
Does it work for small data sets?
It needs at least 4 values. With fewer than about 10, quartiles are unstable, so treat results with care.
Is the Outlier Detector (IQR Method) free?
Yes, the Outlier Detector (IQR Method) is free. The first time you see your first result, you are asked for your name and WhatsApp number once. After that, this and every other Uncodemy tool opens straight away without the form.