Plot Normal Distribution Using Median

 

Step-by-Step Guide to Plot Normal Distribution Using Median

Step 1: Calculate the Median and Interquartile Range

1. Create Measures for Median and Interquartile Range (IQR):

   • Go to the Modeling tab in Power BI Desktop.

   • Click on "New Measure" and create the following measures.

dax

MedianTaskAge = MEDIAN('Tasks'[Task Age])

dax

Percentile25 = PERCENTILEX.INC('Tasks', 'Tasks'[Task Age], 0.25)

dax

Percentile75 = PERCENTILEX.INC('Tasks', 'Tasks'[Task Age], 0.75)

dax

IQRTaskAge = [Percentile75] - [Percentile25]

Step 2: Create a Normal Distribution Function Using Median and IQR

1. Create a Measure for the Normal Distribution Function:

   • Click on "New Measure" again and create a measure for the normal distribution function.

dax

NormalDistUsingMedian = 
VAR Median = [MedianTaskAge]
VAR IQR = [IQRTaskAge]
VAR Value = SELECTEDVALUE('Tasks'[Task Age])
RETURN
1 / (IQR * SQRT(2 * PI())) * EXP(-0.5 * ((Value - Median) / IQR) ^ 2)

Step 3: Create a Supporting Table for the Distribution

1. Create a New Table:

   • Go to the Modeling tab and click on "New Table".

   • Create a table with a range of values to plot the normal distribution.

dax

NormalDistTable = GENERATESERIES(MIN('Tasks'[Task Age]), MAX('Tasks'[Task Age]), 1)

Step 4: Create the Normal Distribution Values Using Median

1. Create a New Column in the Supporting Table:

   • Add a calculated column in the NormalDistTable to evaluate the normal distribution function.

dax

NormalDistValueUsingMedian = 
VAR Median = [MedianTaskAge]
VAR IQR = [IQRTaskAge]
VAR Value = [Value]
RETURN
1 / (IQR * SQRT(2 * PI())) * EXP(-0.5 * ((Value - Median) / IQR) ^ 2)

Step 5: Plot the Normal Distribution in a Line Chart

1. Create a Line Chart:

   • Go to the Report view and insert a Line chart visual.

   • Add the NormalDistTable's Value column to the X-axis.

   • Add the NormalDistValueUsingMedian column to the Y-axis.

Explanation:

• MedianTaskAge: Calculates the median of Task Age.

• Percentile25 and Percentile75: Calculate the 25th and 75th percentiles of Task Age, respectively.

• IQRTaskAge: Calculates the interquartile range (IQR) of Task Age.

• NormalDistUsingMedian: Calculates the normal distribution values based on the median and IQR.

• NormalDistTable: Creates a series of values to plot the normal distribution curve.

• NormalDistValueUsingMedian: Calculates the normal distribution function for each value in the supporting table using the median and IQR.

By following these steps, you can create a normal distribution plot for "Task Age" in Power BI using the median instead of the mean, providing a visualization based on the median-centered distribution.