to sum up:
The outlier is estimated using 1.5IQR, IQR=Q3-Q1, which is a value between 25%-75%,
In theory, Q4-Q3 should have only 0.5 IQR, and more than 1.5 IQR indicates that the data is abnormal.
The upper limit is the maximum value in the non-anomalous range. The lower limit is the minimum value in the non-abnormal range.
The first thing to know is how to calculate the interquartile range?
Interquartile range IQR=Q3-Q1,
Then the upper limit=Q3+1.5IQR, the lower limit=Q1-1.5IQR
Specific numerical calculation:
https://baijiahao.baidu.com/s?id=1591167651227320027&wfr=spider&for=pc
On both sides are the max value and min value, the abnormal value line is not displayed.
The following are specific examples of box plots:
Figure 2. Example
This set of data shows:
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Minimum ( minimum )=5
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Lower quartile ( Q1 )=7
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Median ( Med - Q2)=8.5
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Upper quartile ( Q3 )=9
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Maximum ( maximum )=10
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Mean=8
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Interquartile range=(\displaystyle Q3-Q1)=2 (i.e. ΔQ)
In the interval Q3+1.5ΔQ, the value outside Q1-1.5ΔQ is regarded as farout.
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farout: Not displayed on the map, only a symbol ∇.
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Maximum value range: Q3+1.5ΔQ
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Minimum interval: Q1-1.5ΔQ
The maximum and minimum values are generated in this interval. Values outside the interval are considered outlier and displayed on the graph.
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mild outlier = 3.5
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extreme outlier = 0.5
https://baike.baidu.com/item/%E7%AE%B1%E5%BD%A2%E5%9B%BE/10671164?fr=aladdin