# W ’s of Box and Whisker Plot

*Let us discuss on ( What, Why, When and How) a Box Plot.*

*A Box and Whisker Plot often called the Box plot is used to show the distribution of values along an axis. It is used to visualize five values in a dataset for the selected column(s) which is called the five number summary.*

*Let us understand the Five number summary in detail.*

*The Five number summary refers to the Minimum value, First Quartile (Q1), Median (Second Quartile Q2), Third quartile(Q3) and the Maximum value.*

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*The Median (50th percentile, Q2) is the value separating the higher half of a data sample from the lower half. In other words, it is the “middle” value of a data set.*

*First quartile (Q1/25th Percentile**): The values between the smallest number and the median of the dataset.*

*Third quartile (Q3/75th Percentile)**: The values between the median and the highest value of the dataset.*

*Minimum value** is calculated as Q1 -1.5*IQR*

*Maximum value **is calculated as Q3 + 1.5*IQR*

*Inter-quartile range:** The middle 50% of values fall within the inter-quartile range. Tableau draws a box around the interquartile range. The quartiles are called **Hinge** and **Whiskers** in Tableau.*

*Whiskers** are the lines extending from the box on both the sides. They typically extend to 1.5*of the interquartile range to set boundary. Hence this plot is called the Box and whisker plot, the points beyond which would be considered **Outliers**.*

*When to use box plot*

*Box plot can be specifically used to find*

*The key values such as the minimum, median, maximum, etc.**Existence of outliers and their values**Skewness and its direction**If the data are symmetrical**How tightly the data is grouped*

*How to make a Box plot*

*Let us make a Box plot that shows Discount by region and product Category.*

*Connect to Sample -Superstore data source**Drag the Category to columns and Discount to rows*

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*Tableau creates a Bar chart by default*

*3.Now drag the Region to the columns, a bar chart as shown in the image is formed.*

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*4.Next Click show me in the tool bar and select the Box and Whisker plot type*

*5.Tableau displays a Box plot. We may notice that there are very few marks in each Box plot. Also, the regions from the column are shifted to the marks card.*

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*6.Drag the Regions back to the columns and we find that the horizontal lines are flattened, this is because the Box plot is based on a single mark and the data is aggregated in the current view*

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*7.Now Disaggregate data by selecting Analysis> Aggregate measures*

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*Instead of a single mark we can see a range of marks.*

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*8.Click the swap button to swap the axes,*

*The Box plot now flows Horizontally*

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*9.Right click the bottom axis and select the Edit Reference line where we can select an interesting color in the Fill drop down list.*

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*10.Box plot is now created with the selected color.*

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*By hovering across each plot, we can Interpret that there are outliers and the Discount provided to each Category across the Region.*