IQR

IQR(interquartile range)=Q1-Q3

• Top whisker: Top box (Q1) + 1.5 x interquartile range (Q1-Q3)
• Top box (Q1) below this value are 75% all the data points.
• Median (Q2)
• interquartile range 50% of all the data point are within this range.
• Bottom box (Q3) above this value are 75% of all the data points
• Bottom whisker: Bottom box (Q3) - 1.5 x interquartile range (Q1-Q3)
• o outliers between 1.5 and 3 times the interquartile range
• + extreme outliers above 3x the interquartile range

http://en.wikipedia.org/wiki/Boxplot