Box plot doesn't show upper or lower whiskers

As the image shows, I do not understand why some boxplot doesn't have whiskers. I had already read the documentation, but I didn't find an aswer. I hope some of you could help me, thanks.

Answer 1

[dpb]

The range of the two variables is so tight there simply isn't sufficient resolution on the plot -- try

ylim([0.25 0.30])

and I suspect you'll then be able to see them.