Box Plot
Box Plot
General idea:
- IQR = Q3 - Q1 - the length of the box
- whiskers (fences) capture data outside of the box
boxplot(..., range=0, ...)
boxplot(..., horizontal=T, ...) // horizontal boxplot
range=0
means that it will show usual box plot.
Modified Box Plot
Modified box plot can be used to show Outliers
- IQR (Inter Quartile Range) - difference between 3rd and 1st quartile
- Inner fences - the values that are 1.5 times the IQR beyond the 1st and 3rd quartile
- Lower inner fence = 1st quartile - (1.5 x IQR)
- Upper inner fence = 3rd quartile + (1.5 x IQR)
- observations beyond the whiskers (fences) are outliers and marked with dots
In R
- by default
boxplot
shows modified box plot
-
IQR(data)
shows the IQR
We can calculate all 5 number values for all quantitative variables associated with a specific category.
- And for each category get a box plot
- With box plots, we also can see how two values interact
-
R
boxplot(d$a ~ as.factor(d$f))
- it will show separate boxplot of values in $a$ for each values of $f$
-
boxplot(d$a ~ as.factor(d$f), col=c("blue","orange"), names=c("yes","no"), varwidth=T)
- if we want to show how much data is there for each factor,
- we can make the with of the boxes proportional to the volume of data
- using
varwidth=T
-
Box Plot with Other Plots
Box plots are nice to combine with other plots
See Also
Sources