# How to draw a boxplot with whiskers correctly?

I want to draw a boxplot with whiskers where a lower bound is equal to $$Q1 - 1.5 IQR$$ and an upper bound is equal to $$Q3 + 1.5 IQR$$, where $$Q1$$ is a lower quantile, $$Q3$$ is an upper quantile and $$IQR$$ ia an interquantile range.

My observations are positive, but the value $$Q1 - 1.5 IQR$$ is below $$0$$. My question is:

Where should I put a lower bound of whiskers on a boxplot: in the point $$Q1 - 1.5 IQR$$ (which is negative) or in the point equal to $$0$$, because all my observations are positive?

• What do you by mean lower bound? The $1.5 \times IQR$ is a rule of thumb to highlight potential outliers. – Karl Oct 30 '18 at 13:50
• I suggest using the lowest data value if none are outliers. – Karl Oct 30 '18 at 13:53

## 1 Answer

The whiskers should extend to the most extreme data points satisfying the criterion that they lie within $$Q1-1.5IQR$$ and $$Q3+1.5IQR$$ from the respective box edges.

e.g. see here and read about 'range'

• Thank you for your response. – MathMen Oct 30 '18 at 14:11