Re: Box and whisker plots.

Question

If 3 is an outlier and a minimum, does the minimum change to the next highest number that is not an outlier?

 

If 3 remains the minimum, then the whisker doesn't really indicate the minimum, does it?

 

 

Answer 1

In a box and whisker plot, outliers are often indicated by an asterisk beyond the end of the whisker. 

 

Depending on how the plot is made (which often depends on who / what software made the plot), the whiskers will go all the way out to the max/min values, or they will end at the "fences" (see below), determined by the quartiles and the IQR, with outliers indicated individually as points or asterisks. 

 

Unless an outlier is discarded (for a really good reason, not just because it's an outlier), it will still be used in all the calculations. 

 

So 3 is still the minimum. 

 

Fences are usually defined as Q₁ − 1.5(IQR) and Q₃ + 1.5(IQR), where Q₁ and Q₃ are the lower and upper quartiles, respectively, and IQR is the Inter-Quartile Range, Q₃ − Q₁.  Anything outside the "fences" are often considered outliers. 

 

Sometimes, these are called the "inner fences", with outer fences being further out (use 3(IQR) in the above definitions for outer fences).  Anything outside the outer fences is called an extreme outlier! 

 

The image found at the address below might help some; 

 

http://www.okstate.edu/sas/v7/sashtml/books/qc/chap43/images/bstyle2a.gif